如何在 Java 中限制 JPasswordField 中的数字位数?\
javaobject oriented programmingprogramming更新于 2024/5/9 23:31:00
JPasswordField 是 JTextField 的子类，JPasswordField 中输入的每个字符都可以用 echo 字符替换。这允许机密输入密码。JPasswordField 的重要方法是 getPassword()、getText()、getAccessibleContext() 等。默认情况下，我们可以在 JPasswordField 中输入任意数量的数字。如果我们想通过实现 DocumentFilter 类 来限制用户输入的数字，则需要重写 replace() 方法。
语法
public void replace(DocumentFilter.FilterBypass fb, int offset, int length, String text, AttributeSet attrs) throws BadLocationException
示例
import java.awt.*;
import java.awt.*;
import javax.swing.*;
import javax.swing.text.*;
public class JPasswordFieldDigitLimitTest extends JFrame {
private JPasswordField passwordField;
private JPanel panel;
public JPasswordFieldDigitLimitTest() {
panel = new JPanel();
((FlowLayout) panel.getLayout()).setHgap(2);
panel.add(new JLabel("Enter Pin: "));
passwordField = new JPasswordField(4);
PlainDocument document = (PlainDocument) passwordField.getDocument();
document.setDocumentFilter(new DocumentFilter() {
@Override
public void replace(DocumentFilter.FilterBypass fb, int offset, int length, String text, AttributeSet attrs) throws BadLocationException {
String string = fb.getDocument().getText(0, fb.getDocument().getLength()) + text;
if (string.length() <= 4) {
super.replace(fb, offset, length, text, attrs);
}
}
});
panel.add(passwordField);
add(panel);
setSize(400, 300);
setDefaultCloseOperation(EXIT_ON_CLOSE);
setLocationRelativeTo(null);
setVisible(true);
}
public static void main(String[] args) {
new JPasswordFieldDigitLimitTest();
}
}
输出
