怎样知道上一次焦点是不是在某个空间上

Question

比如我有文本框A,B,C,D和一个按钮。
当点击按钮时，我想知道上一次焦点是否在A文本框上，可以做到么？

Answer 1

这是我写的代码。
import javax.swing.JOptionPane;/**
 *
 * @author  WenLiang
 */
public class t extends javax.swing.JFrame {
String f = ""; /** Creates new form t */
public t() {
initComponents();
this.setLocationRelativeTo(null);
} //GEN-BEGIN:initComponents
// <editor-fold defaultstate="collapsed" desc="Generated Code">
private void initComponents() { A = new javax.swing.JTextField();
B = new javax.swing.JTextField();
C = new javax.swing.JTextField();
jButton1 = new javax.swing.JButton(); setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE); A.setText("A");
A.addFocusListener(new java.awt.event.FocusAdapter() {
public void focusLost(java.awt.event.FocusEvent evt) {
AFocusLost(evt);
}
}); B.setText("B");
B.addFocusListener(new java.awt.event.FocusAdapter() {
public void focusLost(java.awt.event.FocusEvent evt) {
BFocusLost(evt);
}
}); C.setText("C");
C.addFocusListener(new java.awt.event.FocusAdapter() {
public void focusLost(java.awt.event.FocusEvent evt) {
CFocusLost(evt);
}
}); jButton1.setText("\u6309\u94ae");
jButton1.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
jButton1ActionPerformed(evt);
}
}); javax.swing.GroupLayout layout = new javax.swing.GroupLayout(
getContentPane());
getContentPane().setLayout(layout);
layout
.setHorizontalGroup(layout
.createParallelGroup(
javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(
layout
.createSequentialGroup()
.addGap(41, 41, 41)
.addGroup(
layout
.createParallelGroup(
javax.swing.GroupLayout.Alignment.TRAILING,
false)
.addComponent(
jButton1,
javax.swing.GroupLayout.Alignment.LEADING,
javax.swing.GroupLayout.DEFAULT_SIZE,
javax.swing.GroupLayout.DEFAULT_SIZE,
Short.MAX_VALUE)
.addComponent(
A,
javax.swing.GroupLayout.Alignment.LEADING,
javax.swing.GroupLayout.DEFAULT_SIZE,
98,
Short.MAX_VALUE)
.addComponent(
B,
javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(
C,
javax.swing.GroupLayout.Alignment.LEADING,
javax.swing.GroupLayout.DEFAULT_SIZE,
206,
Short.MAX_VALUE))
.addContainerGap(33, Short.MAX_VALUE)));
layout
.setVerticalGroup(layout
.createParallelGroup(
javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(
layout
.createSequentialGroup()
.addGap(38, 38, 38)
.addComponent(
A,
javax.swing.GroupLayout.PREFERRED_SIZE,
javax.swing.GroupLayout.DEFAULT_SIZE,
javax.swing.GroupLayout.PREFERRED_SIZE)
.addPreferredGap(
javax.swing.LayoutStyle.ComponentPlacement.RELATED)
.addComponent(
B,
javax.swing.GroupLayout.PREFERRED_SIZE,
javax.swing.GroupLayout.DEFAULT_SIZE,
javax.swing.GroupLayout.PREFERRED_SIZE)
.addPreferredGap(
javax.swing.LayoutStyle.ComponentPlacement.RELATED)
.addComponent(
C,
javax.swing.GroupLayout.PREFERRED_SIZE,
javax.swing.GroupLayout.DEFAULT_SIZE,
javax.swing.GroupLayout.PREFERRED_SIZE)
.addPreferredGap(
javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
.addComponent(jButton1)
.addContainerGap(30, Short.MAX_VALUE))); pack();
}// </editor-fold>
//GEN-END:initComponents private void CFocusLost(java.awt.event.FocusEvent evt) {
f = "C";
} private void BFocusLost(java.awt.event.FocusEvent evt) {
f = "B";
} private void AFocusLost(java.awt.event.FocusEvent evt) {
f = "A";
} private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
JOptionPane.showMessageDialog(this, "按钮按下前焦点在" + f + "控件上");
} /**
 * @param args the command line arguments
 */
public static void main(String args[]) {
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
new t().setVisible(true);
}
});
} //GEN-BEGIN:variables
// Variables declaration - do not modify
private javax.swing.JTextField A;
private javax.swing.JTextField B;
private javax.swing.JTextField C;
private javax.swing.JButton jButton1;
// End of variables declaration//GEN-END:variables}

Answer 2

很强的人啊swing离我是那么的遥远啊！