Java Enter事件不会激活处理程序

Question

I am new to Java events, listeners and handlers. I can write code to create a button click event and a working result. However, I cannot get a simple enter event within a TextField to work.

Notice I do declare and call action listeners, input handlers, and define a resulting method execution. (I import java.awt and javax.swing libraries not shown below.)

public convertStringToCapitalLetters() {
    setTitle("Convert String to All Capital Letters");
    Container c = getContentPane();
    c.setLayout(new GridLayout(2, 2));

    inputLabel = new JLabel("Enter String: ", SwingConstants.LEFT);
    stringTextField = new JTextField(50);
    outputLabel = new JLabel("Capitalized String: ", SwingConstants.LEFT);
    newStringLabel = new JLabel("", SwingConstants.RIGHT);

    c.add(inputLabel);
    c.add(stringTextField);
    c.add(outputLabel);
    c.add(newStringLabel);

    inputHandler = new InputHandler();

    stringTextField.addActionListener(inputHandler);

    setSize(WIDTH, HEIGHT);
    setDefaultCloseOperation(EXIT_ON_CLOSE);
    setVisible(true);
}

private class InputHandler implements ActionListener {

    public void actionPerformed(ActionEvent e) {
        String str, newStr;

        str = stringTextField.getText();
        newStr = str.toUpperCase();

        newStringLabel.setText(String.format("", newStr));
    }
}

public static void main(String[] args) {
    convertStringToCapitalLetters capitalConv = new convertStringToCapitalLetters();
}

Answer 1

I think you just made a very small mistake which is to forget to specify the placeholder %s in String.format()

Try this:

newStringLabel.setText(String.format("%s", newStr));

Answer 2

设置标签的文本时不需要String.format("", newStr)调用，您只需使用

newStringLabel.setText(newStr);