检查 JTextField 是否不为空

Question

我正在尝试为 GUI 创建示例，它从 JTextFiled 中的用户那里获取名称，并为用户显示在 JtextField 中输入的名称的消息，现在我想检查用户是否在按钮上输入而不输入任何事情，我试图在 ActionListener 中使用此方法，但我在编辑器中看到错误，而当我在 ActionListener 之外使用它时，我发现它有效！，请看附件图片

    public class Example01 extends JFrame {

    public JTextField text;
    public Example01() {
        setTitle("Example 01");
        JPanel panel = new JPanel();
        panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS));
        panel.setBorder(BorderFactory.createEmptyBorder(50, 50, 50, 50));
        JLabel label = new JLabel("Enter Your Name : ");
        text = new JTextField();
        text.setSize(30, 10);
        JButton btn1 = new JButton("Enter");

        btn1.addActionListener(new ActionListener() {

        if (text.getText().equals("")) {
            JOptionPane.showMessageDialog(rootPane, "Please enter anything");
        }

            @Override
            public void actionPerformed(ActionEvent e) {
                JOptionPane.showMessageDialog(rootPane, "Hello : " + text.getText());
            }
        });
        panel.add(label);
        panel.add(Box.createRigidArea(new Dimension(0, 20)));
        panel.add(text);
        panel.add(Box.createRigidArea(new Dimension(0, 20)));
        panel.add(btn1);

        add(panel);
        setVisible(true);
        pack();
        setLocationRelativeTo(null);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
    }

}

error message

编辑
问题是因为我将代码放在可执行上下文之外 "a method"

Answer 1

拿...

if (text.getText().equals("")) {
    JOptionPane.showMessageDialog(rootPane, "Please enter anything");
}

并将其放入您的 actionPerformed 方法中...

btn1.addActionListener(new ActionListener() {

    @Override
    public void actionPerformed(ActionEvent e) {
        if (text.getText().equals("")) {
            JOptionPane.showMessageDialog(rootPane, "Please enter anything");
        }
        JOptionPane.showMessageDialog(rootPane, "Hello : " + text.getText());
    }
});

检查 JTextField 是否不为空

Checking if JTextField not empty

java

swing

actionlistener

jtextfield

java-7