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import java.awt.FlowLayout;
import java.awt.event.FocusAdapter;
import java.awt.event.FocusEvent;
import javax.swing.JFrame;
import javax.swing.JTextField;
import javax.swing.text.JTextComponent;
public class Main {
public static void main(String[] argv) throws Exception {
JTextField component = new JTextField(10);
JTextField component1 = new JTextField(10);
component.addFocusListener(new MyFocusListener());
component1.addFocusListener(new MyFocusListener());
JFrame f = new JFrame();
f.setLayout(new FlowLayout());
f.add(component1);
f.add(component);
f.pack();
f.setVisible(true);
}
}
class MyFocusListener extends FocusAdapter {
boolean showingDialog = false;
public void focusGained(FocusEvent evt) {
final JTextComponent c = (JTextComponent) evt.getSource();
String s = c.getText();
for (int i = 0; i < s.length(); i++) {
if (!Character.isDigit(s.charAt(i))) {
c.setSelectionStart(i);
c.setSelectionEnd(i);
break;
}
}
}
public void focusLost(FocusEvent evt) {
final JTextComponent c = (JTextComponent) evt.getSource();
String s = c.getText();
if (evt.isTemporary()) {
return;
}
for (int i = 0; i < s.length(); i++) {
if (!Character.isDigit(s.charAt(i))) {
System.out.println("must only contain digits");
c.requestFocus();
break;
}
}
}
}
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