Q:

This method (setSize, setDefaultCloseOperation... is undefined for the type HelloFrame

I'm trying to make a swing version of the Hello World!!! program in a GUI. But I keep on getting an error like I mentioned in the title. Here is my code:
import javax.swing.*;

public class HelloFrame
{

    public static void main(String[] args)
    {
        new HelloFrame();
    }

    public HelloFrame()
    {
        this.setSize(200, 100);
        this.setDefaultCloseOperation(
            JFrame.EXIT_ON_CLOSE);
        this.setTitle("Hello World!");
        this.setVisible(true);
    }
}

Errors are in:
    this.setSize(200, 100);
    this.setDefaultCloseOperation(
        JFrame.EXIT_ON_CLOSE);
    this.setTitle("Hello World!");
    this.setVisible(true);

I would really appreciate some answers. Thanks!
EDIT 1: Oh yeah! I forgot to mention I'm using java.

A:

In your example, HelloFrame implicitly extends Object. As a result, this refers to an Object, which has no JFrame methods. Instead, let HelloFrame contain a JFrame, as shown below. Also,

I've added a JLabel to give the frame something to display after pack() is invoked.
Swing GUI objects should be constructed and manipulated only on the event dispatch thread.

import java.awt.EventQueue;
import javax.swing.JFrame;
import javax.swing.JLabel;

/** @see https://stackoverflow.com/a/32016671/230513 */
public class HelloFrame {

    private void display() {
        JFrame f = new JFrame("HelloFrame");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setTitle("Hello World!");
        f.add(new JLabel("Hello World! Hello World!"), JLabel.CENTER);
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new HelloFrame()::display);
    }
}

