OverlayLayout是用于排列重疊組件的布局管理器。它的用途是以一些對齊的點為基準將一些組件層疊的放置在布局容器中。
組件的橫軸和縱軸的對齊點介于0.0和1.0之間。橫軸（X軸）上0.0代表組件的左側面，1.0代表組件的右側面；縱軸（Y軸）上0.0和1.0分別代表組件的頂部和底部。
構造函數
public OverlayLayout(Container target)
因為構造函數不會為target對象安裝結果布局管理器，所以我們還必須調用setLayout()來完成此功能。
JPanel p1 = new JPanel();
OverlayLayout overlay = new OverlayLayout(p1);
p1.setLayout(overlay); 為了容易理解，我們來看《Java Swing》中關于OverlayLayout的一段樣例程序，它可以編譯運行。如圖，你可以在輸入框中調節容器中3個按鈕的X，Y軸的值來看他們在容器中的位置是怎樣改變的，多試幾次，你就可以完全理解OverlayLayout。
// OverlayTest.java
// A test of the OverlayLayout manager allowing experimentation.
//
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class OverlayTest extends JFrame 
{
public OverlayTest() {
super("OverlayLayout Test");
setSize(500, 300);
setDefaultCloseOperation(EXIT_ON_CLOSE);
final Container c = getContentPane();
c.setLayout(new GridBagLayout());
final JPanel p1 = new GridPanel();
final OverlayLayout overlay = new OverlayLayout(p1);
p1.setLayout(overlay);
final JButton jb1 = new JButton("B1");
final JButton jb2 = new JButton("B2");
final JButton jb3 = new JButton("B3");
Dimension b1 = new Dimension(60, 50);
Dimension b2 = new Dimension(80, 40);
Dimension b3 = new Dimension(100, 60);
jb1.setMinimumSize(b1);
jb1.setMaximumSize(b1);
jb1.setPreferredSize(b1);
jb2.setMinimumSize(b2);
jb2.setMaximumSize(b2);
jb2.setPreferredSize(b2);
jb3.setMinimumSize(b3);
jb3.setMaximumSize(b3);
jb3.setPreferredSize(b3);
SimpleReporter reporter = new SimpleReporter();
jb1.addActionListener(reporter);
jb2.addActionListener(reporter);
jb3.addActionListener(reporter);
p1.add(jb1);
p1.add(jb2);
p1.add(jb3);
JPanel p2 = new JPanel();
p2.setLayout(new GridLayout(2,6));
p2.add(new JLabel("B1 X", JLabel.CENTER));
p2.add(new JLabel("B1 Y", JLabel.CENTER));
p2.add(new JLabel("B2 X", JLabel.CENTER));
p2.add(new JLabel("B2 Y", JLabel.CENTER));
p2.add(new JLabel("B3 X", JLabel.CENTER));
p2.add(new JLabel("B3 Y", JLabel.CENTER));
p2.add(new JLabel(""));
final JTextField x1 = new JTextField("0.0", 4); // Button1 x alignment
final JTextField y1 = new JTextField("0.0", 4); // Button1 y alignment
final JTextField x2 = new JTextField("0.0", 4);
final JTextField y2 = new JTextField("0.0", 4);
final JTextField x3 = new JTextField("0.0", 4);
final JTextField y3 = new JTextField("0.0", 4);
p2.add(x1);
p2.add(y1);
p2.add(x2);
p2.add(y2);
p2.add(x3);
p2.add(y3);
GridBagConstraints constraints = new GridBagConstraints();
c.add(p1, constraints);
constraints.gridx = 1;
JButton updateButton = new JButton("Update");
updateButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent ae) {
jb1.setAlignmentX(
Float.valueOf(x1.getText().trim()).floatValue());
jb1.setAlignmentY(
Float.valueOf(y1.getText().trim()).floatValue());
jb2.setAlignmentX(
Float.valueOf(x2.getText().trim()).floatValue());
jb2.setAlignmentY(
Float.valueOf(y2.getText().trim()).floatValue());
jb3.setAlignmentX(
Float.valueOf(x3.getText().trim()).floatValue());
jb3.setAlignmentY(
Float.valueOf(y3.getText().trim()).floatValue());
p1.revalidate();
}
});
c.add(updateButton, constraints);
constraints.gridx = 0;
constraints.gridy = 1;
constraints.gridwidth = 2;
c.add(p2, constraints);
}
public static void main(String args[]) {
OverlayTest ot = new OverlayTest();
ot.setVisible(true);
}
public class SimpleReporter implements ActionListener {
public void actionPerformed(ActionEvent ae) {
System.out.println(ae.getActionCommand());
}
}
public class GridPanel extends JPanel {
public void paint(Graphics g) {
super.paint(g);
int w = getSize().width;
int h = getSize().height;
g.setColor(Color.red);
g.drawRect(0,0,w-1,h-1);
g.drawLine(w/2,0,w/2,h);
g.drawLine(0,h/2,w,h/2);
}
}
}
最后提醒，使用OverlayLayout布局管理器關鍵要記住X，Y軸對應組件位置，和容器沒有關系。只要明白這一點，使用還是很簡單方便的，我用OverlayLayout布局管理器clone了一個PhotoShop的工具面板。
