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(duì)齊的點(diǎn)為基準(zhǔn)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(duì)齊點(diǎn)介于0.0和1.0之間。橫軸（X軸）上0.0代表組件的左側(cè)面，1.0代表組件的右側(cè)面；縱軸（Y軸）上0.0和1.0分別代表組件的頂部和底部。
構(gòu)造函數(shù)
public OverlayLayout(Container target)
因?yàn)闃?gòu)造函數(shù)不會(huì)為target對(duì)象安裝結(jié)果布局管理器，所以我們還必須調(diào)用setLayout()來(lái)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(lái)看《Java Swing》中關(guān)于OverlayLayout的一段樣例程序，它可以編譯運(yùn)行。如圖，你可以在輸入框中調(diào)節(jié)容器中3個(gè)按鈕的X，Y軸的值來(lái)看他們?cè)谌萜髦械奈恢檬窃鯓痈淖兊模嘣噹状危憔涂梢酝耆斫釵verlayLayout。
// 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(guān)鍵要記住X，Y軸對(duì)應(yīng)組件位置，和容器沒(méi)有關(guān)系。只要明白這一點(diǎn)，使用還是很簡(jiǎn)單方便的，我用OverlayLayout布局管理器clone了一個(gè)PhotoShop的工具面板。
