<commit_before>/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.lang3;

import java.io.File;

/**
 * <p>
 * Helpers for {@code java.lang.System}.
 * </p>
 * <p>
 * If a system property cannot be read due to security restrictions, the corresponding field in this class will be set
 * to {@code null} and a message will be written to {@code System.err}.
 * </p>
 * <p>
 * #ThreadSafe#
 * </p>
 *
 * @since 1.0
 * @version $Id$
 */
public class SystemUtils {

    /**
     * The prefix String for all Windows OS.
     */
    private static final String OS_NAME_WINDOWS_PREFIX = "Windows";

    // System property constants
    // -----------------------------------------------------------------------
    // These MUST be declared first. Other constants depend on this.

    /**
     * The System property key for the user home directory.
     */
    private static final String USER_HOME_KEY = "user.home";

    /**
     * The System property key for the user directory.
     */
    private static final String USER_DIR_KEY = "user.dir";

    /**
     * The System property key for the Java IO temporary directory.
     */
    private static final String JAVA_IO_TMPDIR_KEY = "java.io.tmpdir";

    /**
     * The System property key for the Java home directory.
     */
    private static final String JAVA_HOME_KEY = "java.home";

    /**
     * <p>
     * The {@code awt.toolkit} System Property.
     * </p>
     * <p>
     * Holds a class name, on Windows XP this is {@code sun.awt.windows.WToolkit}.
     * </p>
     * <p>
     * <b>On platforms without a GUI, this value is {@code null}.</b>
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since 2.1
     */
    public static final String AWT_TOOLKIT = getSystemProperty("awt.toolkit");

    /**
     * <p>
     * The {@code file.encoding} System Property.
     * </p>
     * <p>
     * File encoding, such as {@code Cp1252}.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since 2.0
     * @since Java 1.2
     */
    public static final String FILE_ENCODING = getSystemProperty("file.encoding");

    /**
     * <p>
     * The {@code file.separator} System Property. 
     * The file separator is:
     * <ul>
     * <li>{@code "/"}</code> on UNIX</li>
     * <li>{@code "\"}</code> on Windows.</li>
     * </ul>
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.1
     */
    public static final String FILE_SEPARATOR = getSystemProperty("file.separator");

    /**
     * <p>
     * The {@code java.awt.fonts} System Property.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since 2.1
     */
    public static final String JAVA_AWT_FONTS = getSystemProperty("java.awt.fonts");

    /**
     * <p>
     * The {@code java.awt.graphicsenv} System Property.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since 2.1
     */
    public static final String JAVA_AWT_GRAPHICSENV = getSystemProperty("java.awt.graphicsenv");

    /**
     * <p>
     * The {@code java.awt.headless} System Property. The value of this property is the String {@code "true"} or
     * {@code "false"}.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @see #isJavaAwtHeadless()
     * @since 2.1
     * @since Java 1.4
     */
    public static final String JAVA_AWT_HEADLESS = getSystemProperty("java.awt.headless");

    /**
     * <p>
     * The {@code java.awt.printerjob} System Property.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since 2.1
     */
    public static final String JAVA_AWT_PRINTERJOB = getSystemProperty("java.awt.printerjob");

    /**
     * <p>
     * The {@code java.class.path} System Property. Java class path.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.1
     */
    public static final String JAVA_CLASS_PATH = getSystemProperty("java.class.path");

    /**
     * <p>
     * The {@code java.class.version} System Property. Java class format version number.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.1
     */
    public static final String JAVA_CLASS_VERSION = getSystemProperty("java.class.version");

    /**
     * <p>
     * The {@code java.compiler} System Property. Name of JIT compiler to use. First in JDK version 1.2. Not used in Sun
     * JDKs after 1.2.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.2. Not used in Sun versions after 1.2.
     */
    public static final String JAVA_COMPILER = getSystemProperty("java.compiler");

    /**
     * <p>
     * The {@code java.endorsed.dirs} System Property. Path of endorsed directory or directories.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.4
     */
    public static final String JAVA_ENDORSED_DIRS = getSystemProperty("java.endorsed.dirs");

    /**
     * <p>
     * The {@code java.ext.dirs} System Property. Path of extension directory or directories.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.3
     */
    public static final String JAVA_EXT_DIRS = getSystemProperty("java.ext.dirs");

    /**
     * <p>
     * The {@code java.home} System Property. Java installation directory.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.1
     */
    public static final String JAVA_HOME = getSystemProperty(JAVA_HOME_KEY);

    /**
     * <p>
     * The {@code java.io.tmpdir} System Property. Default temp file path.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.2
     */
    public static final String JAVA_IO_TMPDIR = getSystemProperty(JAVA_IO_TMPDIR_KEY);

    /**
     * <p>
     * The {@code java.library.path} System Property. List of paths to search when loading libraries.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.2
     */
    public static final String JAVA_LIBRARY_PATH = getSystemProperty("java.library.path");

    /**
     * <p>
     * The {@code java.runtime.name} System Property. Java Runtime Environment name.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since 2.0
     * @since Java 1.3
     */
    public static final String JAVA_RUNTIME_NAME = getSystemProperty("java.runtime.name");

    /**
     * <p>
     * The {@code java.runtime.version} System Property. Java Runtime Environment version.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since 2.0
     * @since Java 1.3
     */
    public static final String JAVA_RUNTIME_VERSION = getSystemProperty("java.runtime.version");

    /**
     * <p>
     * The {@code java.specification.name} System Property. Java Runtime Environment specification name.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.2
     */
    public static final String JAVA_SPECIFICATION_NAME = getSystemProperty("java.specification.name");

    /**
     * <p>
     * The {@code java.specification.vendor} System Property. Java Runtime Environment specification vendor.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.2
     */
    public static final String JAVA_SPECIFICATION_VENDOR = getSystemProperty("java.specification.vendor");

    /**
     * <p>
     * The {@code java.specification.version} System Property. Java Runtime Environment specification version.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.3
     */
    public static final String JAVA_SPECIFICATION_VERSION = getSystemProperty("java.specification.version");
    private static final JavaVersion JAVA_SPECIFICATION_VERSION_AS_ENUM = JavaVersion.get(JAVA_SPECIFICATION_VERSION);

    /**
     * <p>
     * The {@code java.util.prefs.PreferencesFactory} System Property. A class name.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since 2.1
     * @since Java 1.4
     */
    public static final String JAVA_UTIL_PREFS_PREFERENCES_FACTORY =
        getSystemProperty("java.util.prefs.PreferencesFactory");

    /**
     * <p>
     * The {@code java.vendor} System Property. Java vendor-specific string.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.1
     */
    public static final String JAVA_VENDOR = getSystemProperty("java.vendor");

    /**
     * <p>
     * The {@code java.vendor.url} System Property. Java vendor URL.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.1
     */
    public static final String JAVA_VENDOR_URL = getSystemProperty("java.vendor.url");

    /**
     * <p>
     * The {@code java.version} System Property. Java version number.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.1
     */
    public static final String JAVA_VERSION = getSystemProperty("java.version");

    /**
     * <p>
     * The {@code java.vm.info} System Property. Java Virtual Machine implementation info.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since 2.0
     * @since Java 1.2
     */
    public static final String JAVA_VM_INFO = getSystemProperty("java.vm.info");

    /**
     * <p>
     * The {@code java.vm.name} System Property. Java Virtual Machine implementation name.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.2
     */
    public static final String JAVA_VM_NAME = getSystemProperty("java.vm.name");

    /**
     * <p>
     * The {@code java.vm.specification.name} System Property. Java Virtual Machine specification name.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.2
     */
    public static final String JAVA_VM_SPECIFICATION_NAME = getSystemProperty("java.vm.specification.name");

    /**
     * <p>
     * The {@code java.vm.specification.vendor} System Property. Java Virtual Machine specification vendor.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.2
     */
    public static final String JAVA_VM_SPECIFICATION_VENDOR = getSystemProperty("java.vm.specification.vendor");

    /**
     * <p>
     * The {@code java.vm.specification.version} System Property. Java Virtual Machine specification version.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.2
     */
    public static final String JAVA_VM_SPECIFICATION_VERSION = getSystemProperty("java.vm.specification.version");

    /**
     * <p>
     * The {@code java.vm.vendor} System Property. Java Virtual Machine implementation vendor.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.2
     */
    public static final String JAVA_VM_VENDOR = getSystemProperty("java.vm.vendor");

    /**
     * <p>
     * The {@code java.vm.version} System Property. Java Virtual Machine implementation version.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.2
     */
    public static final String JAVA_VM_VERSION = getSystemProperty("java.vm.version");

    /**
     * <p>
     * The {@code line.separator} System Property. Line separator (<code>&quot;\n&quot;</code> on UNIX).
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.1
     */
    public static final String LINE_SEPARATOR = getSystemProperty("line.separator");

    /**
     * <p>
     * The {@code os.arch} System Property. Operating system architecture.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.1
     */
    public static final String OS_ARCH = getSystemProperty("os.arch");

    /**
     * <p>
     * The {@code os.name} System Property. Operating system name.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.1
     */
    public static final String OS_NAME = getSystemProperty("os.name");

    /**
     * <p>
     * The {@code os.version} System Property. Operating system version.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.1
     */
    public static final String OS_VERSION = getSystemProperty("os.version");

    /**
     * <p>
     * The {@code path.separator} System Property. Path separator (<code>&quot;:&quot;</code> on UNIX).
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.1
     */
    public static final String PATH_SEPARATOR = getSystemProperty("path.separator");

    /**
     * <p>
     * The {@code user.country} or {@code user.region} System Property. User's country code, such as {@code GB}. First
     * in Java version 1.2 as {@code user.region}. Renamed to {@code user.country} in 1.4
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since 2.0
     * @since Java 1.2
     */
    public static final String USER_COUNTRY = getSystemProperty("user.country") == null ?
            getSystemProperty("user.region") : getSystemProperty("user.country");

    /**
     * <p>
     * The {@code user.dir} System Property. User's current working directory.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.1
     */
    public static final String USER_DIR = getSystemProperty(USER_DIR_KEY);

    /**
     * <p>
     * The {@code user.home} System Property. User's home directory.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.1
     */
    public static final String USER_HOME = getSystemProperty(USER_HOME_KEY);

    /**
     * <p>
     * The {@code user.language} System Property. User's language code, such as {@code "en"}.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since 2.0
     * @since Java 1.2
     */
    public static final String USER_LANGUAGE = getSystemProperty("user.language");

    /**
     * <p>
     * The {@code user.name} System Property. User's account name.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.1
     */
    public static final String USER_NAME = getSystemProperty("user.name");

    /**
     * <p>
     * The {@code user.timezone} System Property. For example: {@code "America/Los_Angeles"}.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since 2.1
     */
    public static final String USER_TIMEZONE = getSystemProperty("user.timezone");

    // Java version checks
    // -----------------------------------------------------------------------
    // These MUST be declared after those above as they depend on the
    // values being set up

    /**
     * <p>
     * Is {@code true} if this is Java version 1.1 (also 1.1.x versions).
     * </p>
     * <p>
     * The field will return {@code false} if {@link #JAVA_VERSION} is {@code null}.
     * </p>
     */
    public static final boolean IS_JAVA_1_1 = getJavaVersionMatches("1.1");

    /**
     * <p>
     * Is {@code true} if this is Java version 1.2 (also 1.2.x versions).
     * </p>
     * <p>
     * The field will return {@code false} if {@link #JAVA_VERSION} is {@code null}.
     * </p>
     */
    public static final boolean IS_JAVA_1_2 = getJavaVersionMatches("1.2");

    /**
     * <p>
     * Is {@code true} if this is Java version 1.3 (also 1.3.x versions).
     * </p>
     * <p>
     * The field will return {@code false} if {@link #JAVA_VERSION} is {@code null}.
     * </p>
     */
    public static final boolean IS_JAVA_1_3 = getJavaVersionMatches("1.3");

    /**
     * <p>
     * Is {@code true} if this is Java version 1.4 (also 1.4.x versions).
     * </p>
     * <p>
     * The field will return {@code false} if {@link #JAVA_VERSION} is {@code null}.
     * </p>
     */
    public static final boolean IS_JAVA_1_4 = getJavaVersionMatches("1.4");

    /**
     * <p>
     * Is {@code true} if this is Java version 1.5 (also 1.5.x versions).
     * </p>
     * <p>
     * The field will return {@code false} if {@link #JAVA_VERSION} is {@code null}.
     * </p>
     */
    public static final boolean IS_JAVA_1_5 = getJavaVersionMatches("1.5");

    /**
     * <p>
     * Is {@code true} if this is Java version 1.6 (also 1.6.x versions).
     * </p>
     * <p>
     * The field will return {@code false} if {@link #JAVA_VERSION} is {@code null}.
     * </p>
     */
    public static final boolean IS_JAVA_1_6 = getJavaVersionMatches("1.6");

    /**
     * <p>
     * Is {@code true} if this is Java version 1.7 (also 1.7.x versions).
     * </p>
     * <p>
     * The field will return {@code false} if {@link #JAVA_VERSION} is {@code null}.
     * </p>
     *
     * @since 3.0
     */
    public static final boolean IS_JAVA_1_7 = getJavaVersionMatches("1.7");

    /**
     * <p>
     * Is {@code true} if this is Java version 1.8 (also 1.8.x versions).
     * </p>
     * <p>
     * The field will return {@code false} if {@link #JAVA_VERSION} is {@code null}.
     * </p>
     *
     * @since 3.4
     */
    public static final boolean IS_JAVA_1_8 = getJavaVersionMatches("1.8");

    // Operating system checks
    // -----------------------------------------------------------------------
    // These MUST be declared after those above as they depend on the
    // values being set up
    // OS names from http://www.vamphq.com/os.html
    // Selected ones included - please advise <EMAIL>
    // if you want another added or a mistake corrected

    /**
     * <p>
     * Is {@code true} if this is AIX.
     * </p>
     * <p>
     * The field will return {@code false} if {@code OS_NAME} is {@code null}.
     * </p>
     *
     * @since 2.0
     */
    public static final boolean IS_OS_AIX = getOSMatchesName("AIX");

    /**
     * <p>
     * Is {@code true} if this is HP-UX.
     * </p>
     * <p>
     * The field will return {@code false} if {@code OS_NAME} is {@code null}.
     * </p>
     *
     * @since 2.0
     */
    public static final boolean IS_OS_HP_UX = getOSMatchesName("HP-UX");
    
    /**
     * <p>
     * Is {@code true} if this is IBM OS/400.
     * </p>
     * <p>
     * The field will return {@code false} if {@code OS_NAME} is {@code null}.
     * </p>
     *
     * @since 3.3
     */
    public static final boolean IS_OS_400 = getOSMatchesName("OS/400");

    /**
     * <p>
     * Is {@code true} if this is Irix.
     * </p>
     * <p>
     * The field will return {@code false} if {@code OS_NAME} is {@code null}.
     * </p>
     *
     * @since 2.0
     */
    public static final boolean IS_OS_IRIX = getOSMatchesName("Irix");

    /**
     * <p>
     * Is {@code true} if this is Linux.
     * </p><commit_msg>Remove trailing white spaces<commit_after>/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.lang3;

import java.io.File;

/**
 * <p>
 * Helpers for {@code java.lang.System}.
 * </p>
 * <p>
 * If a system property cannot be read due to security restrictions, the corresponding field in this class will be set
 * to {@code null} and a message will be written to {@code System.err}.
 * </p>
 * <p>
 * #ThreadSafe#
 * </p>
 *
 * @since 1.0
 * @version $Id$
 */
public class SystemUtils {

    /**
     * The prefix String for all Windows OS.
     */
    private static final String OS_NAME_WINDOWS_PREFIX = "Windows";

    // System property constants
    // -----------------------------------------------------------------------
    // These MUST be declared first. Other constants depend on this.

    /**
     * The System property key for the user home directory.
     */
    private static final String USER_HOME_KEY = "user.home";

    /**
     * The System property key for the user directory.
     */
    private static final String USER_DIR_KEY = "user.dir";

    /**
     * The System property key for the Java IO temporary directory.
     */
    private static final String JAVA_IO_TMPDIR_KEY = "java.io.tmpdir";

    /**
     * The System property key for the Java home directory.
     */
    private static final String JAVA_HOME_KEY = "java.home";

    /**
     * <p>
     * The {@code awt.toolkit} System Property.
     * </p>
     * <p>
     * Holds a class name, on Windows XP this is {@code sun.awt.windows.WToolkit}.
     * </p>
     * <p>
     * <b>On platforms without a GUI, this value is {@code null}.</b>
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since 2.1
     */
    public static final String AWT_TOOLKIT = getSystemProperty("awt.toolkit");

    /**
     * <p>
     * The {@code file.encoding} System Property.
     * </p>
     * <p>
     * File encoding, such as {@code Cp1252}.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since 2.0
     * @since Java 1.2
     */
    public static final String FILE_ENCODING = getSystemProperty("file.encoding");

    /**
     * <p>
     * The {@code file.separator} System Property.
     * The file separator is:
     * <ul>
     * <li>{@code "/"}</code> on UNIX</li>
     * <li>{@code "\"}</code> on Windows.</li>
     * </ul>
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.1
     */
    public static final String FILE_SEPARATOR = getSystemProperty("file.separator");

    /**
     * <p>
     * The {@code java.awt.fonts} System Property.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since 2.1
     */
    public static final String JAVA_AWT_FONTS = getSystemProperty("java.awt.fonts");

    /**
     * <p>
     * The {@code java.awt.graphicsenv} System Property.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since 2.1
     */
    public static final String JAVA_AWT_GRAPHICSENV = getSystemProperty("java.awt.graphicsenv");

    /**
     * <p>
     * The {@code java.awt.headless} System Property. The value of this property is the String {@code "true"} or
     * {@code "false"}.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @see #isJavaAwtHeadless()
     * @since 2.1
     * @since Java 1.4
     */
    public static final String JAVA_AWT_HEADLESS = getSystemProperty("java.awt.headless");

    /**
     * <p>
     * The {@code java.awt.printerjob} System Property.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since 2.1
     */
    public static final String JAVA_AWT_PRINTERJOB = getSystemProperty("java.awt.printerjob");

    /**
     * <p>
     * The {@code java.class.path} System Property. Java class path.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.1
     */
    public static final String JAVA_CLASS_PATH = getSystemProperty("java.class.path");

    /**
     * <p>
     * The {@code java.class.version} System Property. Java class format version number.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.1
     */
    public static final String JAVA_CLASS_VERSION = getSystemProperty("java.class.version");

    /**
     * <p>
     * The {@code java.compiler} System Property. Name of JIT compiler to use. First in JDK version 1.2. Not used in Sun
     * JDKs after 1.2.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.2. Not used in Sun versions after 1.2.
     */
    public static final String JAVA_COMPILER = getSystemProperty("java.compiler");

    /**
     * <p>
     * The {@code java.endorsed.dirs} System Property. Path of endorsed directory or directories.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.4
     */
    public static final String JAVA_ENDORSED_DIRS = getSystemProperty("java.endorsed.dirs");

    /**
     * <p>
     * The {@code java.ext.dirs} System Property. Path of extension directory or directories.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.3
     */
    public static final String JAVA_EXT_DIRS = getSystemProperty("java.ext.dirs");

    /**
     * <p>
     * The {@code java.home} System Property. Java installation directory.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.1
     */
    public static final String JAVA_HOME = getSystemProperty(JAVA_HOME_KEY);

    /**
     * <p>
     * The {@code java.io.tmpdir} System Property. Default temp file path.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.2
     */
    public static final String JAVA_IO_TMPDIR = getSystemProperty(JAVA_IO_TMPDIR_KEY);

    /**
     * <p>
     * The {@code java.library.path} System Property. List of paths to search when loading libraries.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.2
     */
    public static final String JAVA_LIBRARY_PATH = getSystemProperty("java.library.path");

    /**
     * <p>
     * The {@code java.runtime.name} System Property. Java Runtime Environment name.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since 2.0
     * @since Java 1.3
     */
    public static final String JAVA_RUNTIME_NAME = getSystemProperty("java.runtime.name");

    /**
     * <p>
     * The {@code java.runtime.version} System Property. Java Runtime Environment version.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since 2.0
     * @since Java 1.3
     */
    public static final String JAVA_RUNTIME_VERSION = getSystemProperty("java.runtime.version");

    /**
     * <p>
     * The {@code java.specification.name} System Property. Java Runtime Environment specification name.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.2
     */
    public static final String JAVA_SPECIFICATION_NAME = getSystemProperty("java.specification.name");

    /**
     * <p>
     * The {@code java.specification.vendor} System Property. Java Runtime Environment specification vendor.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.2
     */
    public static final String JAVA_SPECIFICATION_VENDOR = getSystemProperty("java.specification.vendor");

    /**
     * <p>
     * The {@code java.specification.version} System Property. Java Runtime Environment specification version.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.3
     */
    public static final String JAVA_SPECIFICATION_VERSION = getSystemProperty("java.specification.version");
    private static final JavaVersion JAVA_SPECIFICATION_VERSION_AS_ENUM = JavaVersion.get(JAVA_SPECIFICATION_VERSION);

    /**
     * <p>
     * The {@code java.util.prefs.PreferencesFactory} System Property. A class name.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since 2.1
     * @since Java 1.4
     */
    public static final String JAVA_UTIL_PREFS_PREFERENCES_FACTORY =
        getSystemProperty("java.util.prefs.PreferencesFactory");

    /**
     * <p>
     * The {@code java.vendor} System Property. Java vendor-specific string.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.1
     */
    public static final String JAVA_VENDOR = getSystemProperty("java.vendor");

    /**
     * <p>
     * The {@code java.vendor.url} System Property. Java vendor URL.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.1
     */
    public static final String JAVA_VENDOR_URL = getSystemProperty("java.vendor.url");

    /**
     * <p>
     * The {@code java.version} System Property. Java version number.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.1
     */
    public static final String JAVA_VERSION = getSystemProperty("java.version");

    /**
     * <p>
     * The {@code java.vm.info} System Property. Java Virtual Machine implementation info.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since 2.0
     * @since Java 1.2
     */
    public static final String JAVA_VM_INFO = getSystemProperty("java.vm.info");

    /**
     * <p>
     * The {@code java.vm.name} System Property. Java Virtual Machine implementation name.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.2
     */
    public static final String JAVA_VM_NAME = getSystemProperty("java.vm.name");

    /**
     * <p>
     * The {@code java.vm.specification.name} System Property. Java Virtual Machine specification name.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.2
     */
    public static final String JAVA_VM_SPECIFICATION_NAME = getSystemProperty("java.vm.specification.name");

    /**
     * <p>
     * The {@code java.vm.specification.vendor} System Property. Java Virtual Machine specification vendor.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.2
     */
    public static final String JAVA_VM_SPECIFICATION_VENDOR = getSystemProperty("java.vm.specification.vendor");

    /**
     * <p>
     * The {@code java.vm.specification.version} System Property. Java Virtual Machine specification version.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.2
     */
    public static final String JAVA_VM_SPECIFICATION_VERSION = getSystemProperty("java.vm.specification.version");

    /**
     * <p>
     * The {@code java.vm.vendor} System Property. Java Virtual Machine implementation vendor.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.2
     */
    public static final String JAVA_VM_VENDOR = getSystemProperty("java.vm.vendor");

    /**
     * <p>
     * The {@code java.vm.version} System Property. Java Virtual Machine implementation version.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.2
     */
    public static final String JAVA_VM_VERSION = getSystemProperty("java.vm.version");

    /**
     * <p>
     * The {@code line.separator} System Property. Line separator (<code>&quot;\n&quot;</code> on UNIX).
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.1
     */
    public static final String LINE_SEPARATOR = getSystemProperty("line.separator");

    /**
     * <p>
     * The {@code os.arch} System Property. Operating system architecture.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.1
     */
    public static final String OS_ARCH = getSystemProperty("os.arch");

    /**
     * <p>
     * The {@code os.name} System Property. Operating system name.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.1
     */
    public static final String OS_NAME = getSystemProperty("os.name");

    /**
     * <p>
     * The {@code os.version} System Property. Operating system version.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.1
     */
    public static final String OS_VERSION = getSystemProperty("os.version");

    /**
     * <p>
     * The {@code path.separator} System Property. Path separator (<code>&quot;:&quot;</code> on UNIX).
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.1
     */
    public static final String PATH_SEPARATOR = getSystemProperty("path.separator");

    /**
     * <p>
     * The {@code user.country} or {@code user.region} System Property. User's country code, such as {@code GB}. First
     * in Java version 1.2 as {@code user.region}. Renamed to {@code user.country} in 1.4
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since 2.0
     * @since Java 1.2
     */
    public static final String USER_COUNTRY = getSystemProperty("user.country") == null ?
            getSystemProperty("user.region") : getSystemProperty("user.country");

    /**
     * <p>
     * The {@code user.dir} System Property. User's current working directory.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.1
     */
    public static final String USER_DIR = getSystemProperty(USER_DIR_KEY);

    /**
     * <p>
     * The {@code user.home} System Property. User's home directory.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.1
     */
    public static final String USER_HOME = getSystemProperty(USER_HOME_KEY);

    /**
     * <p>
     * The {@code user.language} System Property. User's language code, such as {@code "en"}.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since 2.0
     * @since Java 1.2
     */
    public static final String USER_LANGUAGE = getSystemProperty("user.language");

    /**
     * <p>
     * The {@code user.name} System Property. User's account name.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since Java 1.1
     */
    public static final String USER_NAME = getSystemProperty("user.name");

    /**
     * <p>
     * The {@code user.timezone} System Property. For example: {@code "America/Los_Angeles"}.
     * </p>
     * <p>
     * Defaults to {@code null} if the runtime does not have security access to read this property or the property does
     * not exist.
     * </p>
     * <p>
     * This value is initialized when the class is loaded. If {@link System#setProperty(String,String)} or
     * {@link System#setProperties(java.util.Properties)} is called after this class is loaded, the value will be out of
     * sync with that System property.
     * </p>
     *
     * @since 2.1
     */
    public static final String USER_TIMEZONE = getSystemProperty("user.timezone");

    // Java version checks
    // -----------------------------------------------------------------------
    // These MUST be declared after those above as they depend on the
    // values being set up

    /**
     * <p>
     * Is {@code true} if this is Java version 1.1 (also 1.1.x versions).
     * </p>
     * <p>
     * The field will return {@code false} if {@link #JAVA_VERSION} is {@code null}.
     * </p>
     */
    public static final boolean IS_JAVA_1_1 = getJavaVersionMatches("1.1");

    /**
     * <p>
     * Is {@code true} if this is Java version 1.2 (also 1.2.x versions).
     * </p>
     * <p>
     * The field will return {@code false} if {@link #JAVA_VERSION} is {@code null}.
     * </p>
     */
    public static final boolean IS_JAVA_1_2 = getJavaVersionMatches("1.2");

    /**
     * <p>
     * Is {@code true} if this is Java version 1.3 (also 1.3.x versions).
     * </p>
     * <p>
     * The field will return {@code false} if {@link #JAVA_VERSION} is {@code null}.
     * </p>
     */
    public static final boolean IS_JAVA_1_3 = getJavaVersionMatches("1.3");

    /**
     * <p>
     * Is {@code true} if this is Java version 1.4 (also 1.4.x versions).
     * </p>
     * <p>
     * The field will return {@code false} if {@link #JAVA_VERSION} is {@code null}.
     * </p>
     */
    public static final boolean IS_JAVA_1_4 = getJavaVersionMatches("1.4");

    /**
     * <p>
     * Is {@code true} if this is Java version 1.5 (also 1.5.x versions).
     * </p>
     * <p>
     * The field will return {@code false} if {@link #JAVA_VERSION} is {@code null}.
     * </p>
     */
    public static final boolean IS_JAVA_1_5 = getJavaVersionMatches("1.5");

    /**
     * <p>
     * Is {@code true} if this is Java version 1.6 (also 1.6.x versions).
     * </p>
     * <p>
     * The field will return {@code false} if {@link #JAVA_VERSION} is {@code null}.
     * </p>
     */
    public static final boolean IS_JAVA_1_6 = getJavaVersionMatches("1.6");

    /**
     * <p>
     * Is {@code true} if this is Java version 1.7 (also 1.7.x versions).
     * </p>
     * <p>
     * The field will return {@code false} if {@link #JAVA_VERSION} is {@code null}.
     * </p>
     *
     * @since 3.0
     */
    public static final boolean IS_JAVA_1_7 = getJavaVersionMatches("1.7");

    /**
     * <p>
     * Is {@code true} if this is Java version 1.8 (also 1.8.x versions).
     * </p>
     * <p>
     * The field will return {@code false} if {@link #JAVA_VERSION} is {@code null}.
     * </p>
     *
     * @since 3.4
     */
    public static final boolean IS_JAVA_1_8 = getJavaVersionMatches("1.8");

    // Operating system checks
    // -----------------------------------------------------------------------
    // These MUST be declared after those above as they depend on the
    // values being set up
    // OS names from http://www.vamphq.com/os.html
    // Selected ones included - please advise <EMAIL>
    // if you want another added or a mistake corrected

    /**
     * <p>
     * Is {@code true} if this is AIX.
     * </p>
     * <p>
     * The field will return {@code false} if {@code OS_NAME} is {@code null}.
     * </p>
     *
     * @since 2.0
     */
    public static final boolean IS_OS_AIX = getOSMatchesName("AIX");

    /**
     * <p>
     * Is {@code true} if this is HP-UX.
     * </p>
     * <p>
     * The field will return {@code false} if {@code OS_NAME} is {@code null}.
     * </p>
     *
     * @since 2.0
     */
    public static final boolean IS_OS_HP_UX = getOSMatchesName("HP-UX");

    /**
     * <p>
     * Is {@code true} if this is IBM OS/400.
     * </p>
     * <p>
     * The field will return {@code false} if {@code OS_NAME} is {@code null}.
     * </p>
     *
     * @since 3.3
     */
    public static final boolean IS_OS_400 = getOSMatchesName("OS/400");

    /**
     * <p>
     * Is {@code true} if this is Irix.
     * </p>
     * <p>
     * The field will return {@code false} if {@code OS_NAME} is {@code null}.
     * </p>
     *
     * @since 2.0
     */
    public static final boolean IS_OS_IRIX = getOSMatchesName("Irix");

    /**
     * <p>
     * Is {@code true} if this is Linux.
     * </p>
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