/*
 * Copyright 2018, TeamDev. All rights reserved.
 *
 * Redistribution and use in source and/or binary forms, with or without
 * modification, must retain the above copyright notice and the following
 * disclaimer.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package io.spine.value;

import org.checkerframework.checker.nullness.qual.Nullable;

import java.io.Serializable;
import java.util.Objects;

import static com.google.common.base.Preconditions.checkNotNull;

/**
 * An abstract base for value holder objects.
 *
 * @param <T> a type of value enclosed in the holder
 * @author Alexander Yevsyukov
 */
public abstract class ValueHolder<T extends Serializable> implements Serializable {

    private static final long serialVersionUID = 0L;
    private final T value;

    protected ValueHolder(T value) {
        this.value = checkNotNull(value);
    }

    /** Returns the stored value. */
    protected T value() {
        return this.value;
    }

    @Override
    public int hashCode() {
        return Objects.hash(value);
    }

    @Override
    public boolean equals(@Nullable Object obj) {
        if (this == obj) {
            return true;
        }

        if (obj == null || getClass() != obj.getClass()) {
            return false;
        }
        ValueHolder other = (ValueHolder) obj;
        return Objects.equals(this.value, other.value);
    }
}

/*
 * Copyright 2018, TeamDev. All rights reserved.
 *
 * Redistribution and use in source and/or binary forms, with or without
 * modification, must retain the above copyright notice and the following
 * disclaimer.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package io.spine.value;

import org.checkerframework.checker.nullness.qual.Nullable;

import java.io.Serializable;
import java.util.Objects;

import static com.google.common.base.Preconditions.checkNotNull;

/**
 * An abstract base for objects that hold {@code Serializable} values.
 *
 * @param <T> a type of value enclosed in the holder
 * @author Alexander Yevsyukov
 */
public abstract class ValueHolder<T extends Serializable> implements Serializable {

    private static final long serialVersionUID = 0L;
    private final T value;

    protected ValueHolder(T value) {
        this.value = checkNotNull(value);
    }

    /** Returns the stored value. */
    protected T value() {
        return this.value;
    }

    @Override
    public int hashCode() {
        return Objects.hash(value);
    }

    @Override
    public boolean equals(@Nullable Object obj) {
        if (this == obj) {
            return true;
        }

        if (obj == null || getClass() != obj.getClass()) {
            return false;
        }
        ValueHolder other = (ValueHolder) obj;
        return Objects.equals(this.value, other.value);
    }
}

Improve Javadoc