Should I use separate ActionListener for each similar action or generic one?

问题

I'm creating a keyboard using buttons with java, when a user clicks on a button labelled from A to Z it will set a JTextField text to A or whatever button they pressed.

I have a seperate class for each button so for A its public class listenser1 implements ActionListener, B its public class listenser2 implements ActionListener is this a good way of doing it?

Also I tried to do do it under one class and used if and if else statements buy using

        if(a.getText().equals("A"))
        {
           input1.setText(input.getText() + "A");       
        }
        .
        .
        .

And this doesn't work, it prints out ABCDEFGHIJKLMNOPQRSTUVWXYZ instead of just the one letter.

回答1:

No, that is not the most efficient way. That takes way too long to write. Instead, try this:

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionListener;

public class Example extends JFrame implements ActionListener {
    private final String[] letters = {"A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z"};
    private JButton[] buttons = new JButton[26];
    private JTextArea text = new JTextArea();

    public Example() {
        super("Example");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        for (int i = 0; i < letters.length; i++) {
            buttons[i] = new JButton(letters[i]);
            buttons[i].addActionListener(this);
            add(buttons[i]);
        }
        add(text);
        pack();
        setVisible(true);
    }

    public void actionPerformed(ActionEvent event) {
        text.append(event.getActionCommand());
    }

    public static void main(String[] args) {
        Example ex = new Example();
    }
}

回答2:

I'd suggest creating one instance of the listener per action. Anonymous inner classes can easily be parameterised by reading an final local.

void addButton(final char letter) {
    JButton button = new JButton(Character.toString(letter));
    button.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent event) {
            input.setText(input.getText() + letter);
        }
    });
    panel.add(button);
}

(I'd suggest going straight for a Document rather than JtextComponent.getText/setText.)

回答3:

Why not you use a single class say like this :

ActionListener commonListener = new ActionListener() {

    public void actionPerformed(ActionEvent e) {
        Object o = e.getSource();
        if (o instanceof JButton) {
            JButton button = (JButton)o;
            String command = (String) button.getActionCommand()();
            input1.setText(command);
        }
    }
};

And you can add this listener to your buttons as :

buttonA = new JButton();
buttonA.addActionListener(commonListener);
buttonA.setActionCommand("A"); // same for others till Z.

Hope this might help you in some way.

回答4:

You can write one parametrized listener:

    private class LetterActionListener implements ActionListener {

        private final char letter;

        public LetterActionListener(char letter) {
            this.letter = letter;
        }

        @Override
        public void actionPerformed(ActionEvent e) {
             input1.setText(input1.getText() + letter);
        }

    }

回答5:

Create one instance of an ActionListener and add it to each button in a loop:

    final JTextField input1;

    ...

    final ActionListener l = new ActionListener() {

        @Override
        public void actionPerformed(ActionEvent e) {
            input1.setText(input1.getText() + ((JButton) e.getSource()).getText());
        }
    };
    for (char c = 'A'; c <= 'Z'; c++) {
        final JButton jButton = new JButton(String.valueOf(c));
        panel.add(jButton);
        jButton.addActionListener(l);
    }

来源：https://stackoverflow.com/questions/9007648/should-i-use-separate-actionlistener-for-each-similar-action-or-generic-one