Learning Java, 4th Edition

BorderLayout

BorderLayout is a little more interesting. It tries to arrange objects in one of five geographical locations, represented by constants in the BorderLayout class: NORTH, SOUTH, EAST, WEST, and CENTER, optionally with some padding between. BorderLayout is the default layout for the content panes of JWindow and JFrame objects. Because each component is associated with a direction, BorderLayout can manage at most five components; it squashes or stretches those components to fit its constraints. As we’ll see in the second example, this means that you often want to have BorderLayout manage sets of components in their own panels.

When we add a component to a container with a border layout, we need to specify both the component and the position at which to add it. To do so, we use an overloaded version of the container’s add() method that takes an additional argument as a constraint. The constraint specifies the name of a position within the BorderLayout.

The following application sets a BorderLayout and adds our five buttons again, named for their locations:

    //file: Border1.java
    import java.awt.*;
    import java.awt.event.*;
    import javax.swing.*;

    public class Border1 extends JPanel {

      public Border1() {
        setLayout(new BorderLayout());
        add(new JButton("North"), BorderLayout.NORTH );
        add(new JButton("South"), BorderLayout.SOUTH );
        add(new JButton("East"), BorderLayout.EAST );
        add(new JButton("West"), BorderLayout.WEST );
        add(new JButton("Center"), BorderLayout.CENTER );
      }

      public ...