Extending the JFrame Class

To write a GUI application, extend the JFrame class. Add GUI components to the extended class. Here is a program that does that.

import java.awt.*; 
import javax.swing.*;

class MyFrame extends JFrame
{
  JPanel panel;
  JLabel label;

  // constructor
  MyFrame( String title )
  {
    super( title );                      // invoke the JFrame constructor
    setSize( 150, 100 );
    setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
    
    setLayout( new FlowLayout() );       // set the layout manager
    label = new JLabel("Hello Swing!");  // construct a JLabel
    add( label );                        // add the label to the JFrame
  }

} 

public class TestFrame2
{
  public static void main ( String[] args )
  {
    MyFrame frame = new MyFrame("Hello"); // construct a MyFrame object
    frame.setVisible( true );             // ask it to become visible
  }
}

The new class is called MyFrame and it is based on JFrame. Exactly how a container arranges the components it contains is determined by a layout manager. The layout manager for this frame is set to FlowLayout using the setLayout() method. (There will be more on this in the next chapter.)

The frame holds a GUI component, a JLabel which displays the words "Hello Swing!" . The JLabel is added to the frame using the add() method.

The main() method in this application does nothing more than construct a MyFrame object and set it visible.