引自：
http://www.aygfsteel.com/leon/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(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)不會為target對象安裝結(jié)果布局管理器，所以我們還必須調(diào)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(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(guān)鍵要記住X，Y軸對應(yīng)組件位置，和容器沒有關(guān)系。只要明白這一點(diǎn)，使用還是很簡單方便的，我用OverlayLayout布局管理器clone了一個(gè)PhotoShop的工具面板。
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