BoxLayout
Because people had so much trouble understanding and working with GridBagLayout, Swing also includes BoxLayout, which gives you many of the benefits of GridBagLayout without the complexity, so you can often use it when you need to do hand-coded layouts (again, if your design becomes too complex, use a GUI builder that generates layouts for you). BoxLayout allows you to control the placement of components either vertically or horizontally, and to control the space between the components using something called “struts and glue.” First, let’s see how to use the BoxLayout directly, in the same way that the other layout managers have been demonstrated:
//: c14:BoxLayout1.java
// Vertical and horizontal BoxLayouts.
// <applet code=BoxLayout1 width=450 height=200></applet>
import javax.swing.*;
import java.awt.*;
import com.bruceeckel.swing.*;
public class BoxLayout1 extends JApplet {
public void init() {
JPanel jpv = new JPanel();
jpv.setLayout(new BoxLayout(jpv, BoxLayout.Y_AXIS));
for(int i = 0; i < 5; i++)
jpv.add(new JButton("jpv " + i));
JPanel jph = new JPanel();
jph.setLayout(new BoxLayout(jph, BoxLayout.X_AXIS));
for(int i = 0; i < 5; i++)
jph.add(new JButton("jph " + i));
Container cp = getContentPane();
cp.add(BorderLayout.EAST, jpv);
cp.add(BorderLayout.SOUTH, jph);
}
public static void main(String[] args) {
Console.run(new BoxLayout1(), 450, 200);
}
} ///:~
The constructor for BoxLayout is a bit different than the other layout managers—you provide the Container that is to be controlled by the BoxLayout as the first argument, and the direction of the layout as the second argument.
To simplify matters, there’s a special container called Box that uses BoxLayout as its native manager. The following example lays out components horizontally and vertically using Box, which has two static methods to create boxes with vertical and horizontal alignment:
//: c14:Box1.java
// Vertical and horizontal BoxLayouts.
// <applet code=Box1 width=450 height=200></applet>
import javax.swing.*;
import java.awt.*;
import com.bruceeckel.swing.*;
public class Box1 extends JApplet {
public void init() {
Box bv = Box.createVerticalBox();
for(int i = 0; i < 5; i++)
bv.add(new JButton("bv " + i));
Box bh = Box.createHorizontalBox();
for(int i = 0; i < 5; i++)
bh.add(new JButton("bh " + i));
Container cp = getContentPane();
cp.add(BorderLayout.EAST, bv);
cp.add(BorderLayout.SOUTH, bh);
}
public static void main(String[] args) {
Console.run(new Box1(), 450, 200);
}
} ///:~
Once you have a Box, you pass it as a second argument when adding components to the content pane.
Struts add space, measured in pixels, between components. To use a strut, you simply add it between the addition of the components that you want spaced apart:
//: c14:Box2.java
// Adding struts.
// <applet code=Box2 width=450 height=300></applet>
import javax.swing.*;
import java.awt.*;
import com.bruceeckel.swing.*;
public class Box2 extends JApplet {
public void init() {
Box bv = Box.createVerticalBox();
for(int i = 0; i < 5; i++) {
bv.add(new JButton("bv " + i));
bv.add(Box.createVerticalStrut(i * 10));
}
Box bh = Box.createHorizontalBox();
for(int i = 0; i < 5; i++) {
bh.add(new JButton("bh " + i));
bh.add(Box.createHorizontalStrut(i * 10));
}
Container cp = getContentPane();
cp.add(BorderLayout.EAST, bv);
cp.add(BorderLayout.SOUTH, bh);
}
public static void main(String[] args) {
Console.run(new Box2(), 450, 300);
}
} ///:~
Struts separate components by a fixed amount, but glue is the opposite; it separates components by as much as possible. Thus it’s more of a “spring” than “glue” (and the design on which this was based was called “springs and struts,” so the choice of the term is a bit mysterious).
//: c14:Box3.java
// Using Glue.
// <applet code=Box3 width=450 height=300></applet>
import javax.swing.*;
import java.awt.*;
import com.bruceeckel.swing.*;
public class Box3 extends JApplet {
public void init() {
Box bv = Box.createVerticalBox();
bv.add(new JLabel("Hello"));
bv.add(Box.createVerticalGlue());
bv.add(new JLabel("Applet"));
bv.add(Box.createVerticalGlue());
bv.add(new JLabel("World"));
Box bh = Box.createHorizontalBox();
bh.add(new JLabel("Hello"));
bh.add(Box.createHorizontalGlue());
bh.add(new JLabel("Applet"));
bh.add(Box.createHorizontalGlue());
bh.add(new JLabel("World"));
bv.add(Box.createVerticalGlue());
bv.add(bh);
bv.add(Box.createVerticalGlue());
getContentPane().add(bv);
}
public static void main(String[] args) {
Console.run(new Box3(), 450, 300);
}
} ///:~
A strut works in one direction, but a rigid area fixes the spacing between components in both directions:
//: c14:Box4.java
// Rigid areas are like pairs of struts.
// <applet code=Box4 width=450 height=300></applet>
import javax.swing.*;
import java.awt.*;
import com.bruceeckel.swing.*;
public class Box4 extends JApplet {
public void init() {
Box bv = Box.createVerticalBox();
bv.add(new JButton("Top"));
bv.add(Box.createRigidArea(new Dimension(120, 90)));
bv.add(new JButton("Bottom"));
Box bh = Box.createHorizontalBox();
bh.add(new JButton("Left"));
bh.add(Box.createRigidArea(new Dimension(160, 80)));
bh.add(new JButton("Right"));
bv.add(bh);
getContentPane().add(bv);
}
public static void main(String[] args) {
Console.run(new Box4(), 450, 300);
}
} ///:~
You should be aware that rigid areas are a bit controversial. Since they use absolute values, some people feel that they cause more trouble than they are worth.
