Learning Java, 4th Edition

Absolute Positioning

It’s possible to set the layout manager to null: no layout control. You might do this to position an object on the display at absolute coordinates. This is usually not the right approach. Components might have different minimum sizes on different platforms, so your interface would not be very portable.

The following example doesn’t use a layout manager and works with absolute coordinates instead:

    //file: MoveButton.java
    import java.awt.*;
    import java.awt.event.*;
    import javax.swing.*;

    public class MoveButton extends JPanel {
      JButton button = new JButton("I Move");

      public MoveButton() {
        setLayout(null);
        add(button);
        button.setSize(button.getPreferredSize());
        button.setLocation(20, 20);
        addMouseListener(new MouseAdapter() {
          public void mousePressed(MouseEvent e) {
          button.setLocation(e.getX(), e.getY());
          }
        });
      }

      public static void main(String[] args) {
        JFrame frame = new JFrame("MoveButton");
        frame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
        frame.setSize(250, 200);
        frame.setLocation(200, 200);
        frame.setContentPane(new MoveButton());
        frame.setVisible(true);
      }
    }

Click in the window area outside of the button to move the button to a new location. Try resizing the window and note that the button stays at a fixed position relative to the window’s upper-left corner.