The Program Explained

When you create a JFrame object it is not automatically displayed. A large application might create several JFrame objects, but might only display one of them at a time. Here is the program again:

import java.awt.*;    // 1. import the application windowing toolkit
import javax.swing.*; // 2. import the Swing classes

public class TestFrame1
{
  // usual main() method 
  public static void main ( String[] args ) 
  {
    JFrame frame                        // 4. a reference to the object
        = new JFrame("Test Frame 1");   // 3. construct a JFrame object
    frame.setSize(200,100);             // 5. set it to 200 pixels wide by 100 high
    frame.setVisible( true );           // 6. ask it to become visible on the screen
    frame.setDefaultCloseOperation
        ( WindowConstants.EXIT_ON_CLOSE );   // 7. say what the close button does
  }
}

Here is an explanation of the program:

1. The AWT is imported since it defines many classes that GUIs use.
• For most programs you must do this.
• (For this simple program, you do not need to do this).
• The AWT is in java.awt.*
2. The Swing package is imported since that is where JFrame is defined.
• For this program, you must do this.
• Notice the 'x' in javax.
3. A JFrame object is constructed.
4. The reference variable frame refers to the JFrame object.
5. The object's setSize() method sets its size.
6. The object's setVisible() method makes it appear on the screen.
7. The object's setDefaultCloseOperation() sets what the "close" button does.