public class Demo extends JFrame {

    public Demo() {

        setBounds(100, 100, 200, 120);

        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);

        Container c = getContentPane();

        c.setLayout(new FlowLayout());

        JTextField tf = new JTextField();//创建文本框

        tf.setColumns(15);//文本框长度

        tf.setText("黑体，加粗，20");

        tf.setFont(new Font("黑体", Font.BOLD, 20));

        c.add(tf);

        JButton btn = new JButton("打印");

        btn.addActionListener(new ActionListener() {

            public void actionPerformed(ActionEvent e) {

                System.out.println(tf.getText());

                tf.setText("");//清空文本

                tf.requestFocus();//获取焦点

            }

        });

        c.add(btn);

        setVisible(true);

    }

    public static void main(String[] args) {

        new Demo();

    }

}

public class Demo extends JFrame {

    public Demo() {

        setBounds(100, 100, 200, 100);

        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);

        Container c = getContentPane();

        c.setLayout(new FlowLayout());

        JPasswordField pf = new JPasswordField();//密码框

        pf.setColumns(15);

        pf.addActionListener(new ActionListener() {//添加动作监听，回车触发

            public void actionPerformed(ActionEvent e) {

                System.out.println(pf.getPassword());

            }

        });

        c.add(pf);

        setVisible(true);

    }

    public static void main(String[] args) {

        new Demo();

    }

}