Question

所以我正在使用此代码根据用户点击来写入文件。我遇到的唯一问题是我在“公共课程编程”上遇到错误。 prog名称是我得到错误的地方：它说：类型prog必须实现继承的抽象方法ActionListener.actionPerformed（ActionEvent）。当我执行添加未加密方法的quickfix时，它会将动作侦听器方法添加到我的代码的末尾但其中没有任何内容。如果我已经在程序中有动作监听器，为什么它告诉我需要实现它们？为什么当我最后添加它时，它是否正常工作，即使它没有任何内容？

import java.awt.*;
import java.awt.event.*;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;

import javax.swing.*;

public class prog extends JFrame implements ActionListener {

//create newLine
final String newLine = System.getProperty("line.separator");

//create buttons
JPanel row1 = new JPanel();
JButton oneLeft = new JButton("oneLeft");
JButton oneRight = new JButton("oneRight");

JPanel row2 = new JPanel();
JButton twoLeft = new JButton("twoLeft");
JButton twoRight = new JButton("twoRight");

JPanel row3 = new JPanel();
JButton threeLeft = new JButton("threeLeft");
JButton threeRight = new JButton("threeRight");


public prog() {
    super("Prog");
    setLookAndFeel();
    setSize(400, 800);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    GridLayout layout = new GridLayout(3, 2);
    setLayout(layout);

    //create outStream for writing to file
    try {
        final File numClicks = new File("numClicks.properties");
        final FileOutputStream outStream = new FileOutputStream(numClicks);
        //add Listeners
        oneLeft.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                try {
                    write(outStream, "oneLeft has been clicked.");
                } catch (IOException e1) {
                    // TODO Auto-generated catch block
                    e1.printStackTrace();
                }
            }
        });

        oneRight.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                try {
                    write(outStream, "oneRight has been clicked.");
                } catch (IOException e1) {
                    // TODO Auto-generated catch block
                    e1.printStackTrace();
                }
            }
        });

        twoLeft.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                try {
                    write(outStream, "twoLeft has been clicked.");
                } catch (IOException e1) {
                    // TODO Auto-generated catch block
                    e1.printStackTrace();
                }
            }
        });

        twoRight.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                try {
                    write(outStream, "twoRight has been clicked.");
                } catch (IOException e1) {
                    // TODO Auto-generated catch block
                    e1.printStackTrace();
                }
            }
        });

        threeLeft.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                try {
                    write(outStream, "threeLeft has been clicked.");
                } catch (IOException e1) {
                    // TODO Auto-generated catch block
                    e1.printStackTrace();
                }
            }
        });

        threeRight.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                try {
                    write(outStream, "threeRight has been clicked.");
                } catch (IOException e1) {
                    // TODO Auto-generated catch block
                    e1.printStackTrace();
                }
            }
        });
    } catch (IOException ioe) {
        System.out.println("The file could not be written.");
    }




    row1.add(oneLeft);
    row1.add(oneRight);
    row2.add(twoLeft);
    row2.add(twoRight);
    row3.add(threeLeft);
    row3.add(threeRight);
    add(row1);
    add(row2);
    add(row3);



    setVisible(true);
}

private void setLookAndFeel() {
    try {
        UIManager.setLookAndFeel("com.sun.java.swing.plaf.nimbus.NimbusLookAndFeel");
    } catch (Exception e) {
        //ignore error
    }
}

void write(FileOutputStream stream, String output) throws IOException {
    output = output + newLine;
    byte[] data = output.getBytes();
    stream.write(data, 0, data.length);
}

public static void main(String[] args) {
    prog progApp = new prog();
}
}

Answer 1

您的班级不应该实施ActionListener。你写的是new ActionListener()，而不是编写一个实现接口的顶级类，你正在编写一些小的内联类（称为匿名内部类）来为你工作。

Answer 2

你implement ActionListener，但实际上并没有实现所需的方法（即actionPerformed()）。因此，您的类对编译器无效。

你需要一个像这样的方法：

@Override
public void actionPerformed(ActionEvent e) {
    // ...
}

接口的工作方式是它定义了implements所具有的类......嗯......实现。这样任何其他进程都可以将其视为ActionListener，并且知道已经定义了某些方法。

Java试图将多态性变成你的朋友的另一种方式。

为了解决下面评论中的问题，看到一个类实现一个接口（如KeyListener）并在不使用它的情况下定义该方法实际上并不罕见。

例如，KeyListener要求您实现三种不同的方法：

public void keyPressed(KeyEvent e);
public void keyReleased(KeyEvent e);
public void keyTyped(KeyEvent e);

假设我只关心keyPressed。然后我的课可能看起来像这样：

public class MyKeyListener implements KeyListener {

    @Override
    public void keyPressed(KeyEvent e) {
        // do stuff
    }

    @Override
    public void keyReleased(KeyEvent e){}

    @Override
    public void keyTyped(KeyEvent e){}

}

代码告诉我，当我已经拥有时，我需要实现ActionListener？

2 个答案: