How to create a jail that occupies all the frame java code example

Example: java create jframe

import javax.swing.JFrame;

public class example {
  public static void main(String[] args){
    JFrame frame = new JFrame();
    frame.setSize(100,100);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOES);
    frame.setTitle("Example Frame");
    frame.setVisible(true);
  }
}