Extending the JFrame Class

The usual way of writing a GUI is to define your own class by extending the JFrame class. Here is a program that does that. It also includes several other new features.

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

class myFrame extends JFrame
{
 
  // paint() is called automatically by the system 
  // after it has displayed most of the frame, but
  // needs to finish by displaying your customizations. 
  public void paint ( Graphics g )
  {
    // draw a String at location x=10 y=50
    g.drawString("A myFrame object", 10, 50 );
  } 
} 

public class TestFrame2
{
  public static void main ( String[] args )
  {
    myFrame frame = new myFrame(); // construct a myFrame object
    frame.setSize( 150, 100 );     // set it to 150 wide by 100 high
    frame.setVisible( true );      // ask it to become visible
  }
}

The Java system has methods which display a frame on the screen when needed (you saw them at work in the previous program). The class myFrame extends the class JFrame. The JFrame class has a paint() method which is called by the Java system (not by you) whenever the frame needs to be displayed. To show a string in the minimal frame display override the paint() method in your class.

The picture shows what the display. As with the previous program, hit control-c in the DOS window to stop the program. (Remember to first click inside the DOS window so the control-c kills the correct program).

frame.paint()   ?