java - 实现继承的抽象方法？

Question

我的代码中出现错误，但我不确定该错误意味着什么，我已尝试研究该错误，但似乎与我的代码无关，有人可以帮助我吗？

我的代码；

import java.io.*;
import java.lang.*;
import java.util.*;
import java.awt.event.*;
import java.awt.*;

import javax.swing.*;


public class Assignment4Test {

public static void main(String[] args) throws IOException {
    Scanner console = new Scanner(System.in);
    BufferedReader in = new BufferedReader(new FileReader("shop-account"));

    final int Username = 3387;
    final int Password = 5183;
    final int AccountNumber = 22334455;

    int EnteredUsername;
    int EnteredPassword;
    int EnteredAccountNumber;
    for (int s = 0; s <= 3; s++) {
        if (s < 3) {
            System.out.println("Enter Username");
            EnteredUsername = console.nextInt();
            System.out.println("Username Entered is " + EnteredUsername);
            System.out.println("Enter Password");
            EnteredPassword = console.nextInt();
            System.out.println("Password Entered is " + EnteredPassword);
            System.out.println("Enter Account Number");
            EnteredAccountNumber = console.nextInt();
            System.out.println("Account Number Entered is " + EnteredAccountNumber);
            if (Username == EnteredUsername && (Password == EnteredPassword)
                    && (AccountNumber == EnteredAccountNumber)) {
                System.out.println("Welcome");
                System.out.println("Account username, password, account number and current balance and shown below;");
                String line;
                while((line = in.readLine()) != null)
                {
                    System.out.println(line);
                }
                new MyFrame().displayGui();
                break;
            } else {
                System.out.println("Wrong Username, Password or Account Number. Please try again.");
            }
        } else {
            System.out.println("3 incorrect enteries detected. Program is terminating, goodbye!");
        }
    }
}

static class MyFrame extends JFrame {

    JMenuBar menubar;

    JMenu TransferAnAmount;
    JMenuItem TransferAnAmountToAnotherAccount;

    JMenu ListRecentTransactions;
    JMenuItem ShowList;

    JMenu DisplayCurrentBalance;
    JMenuItem ShowBalance;

    JMenu ExitProgram;
    JMenuItem Exit;

    public MyFrame() {

        setLayout(new FlowLayout());

        menubar = new JMenuBar();
        setJMenuBar(menubar);

        TransferAnAmount = new JMenu("Transfer An Amount");
        menubar.add(TransferAnAmount);

        ListRecentTransactions = new JMenu("List Recent Transactions");
        menubar.add(ListRecentTransactions);

        DisplayCurrentBalance = new JMenu("Display Current Balance");
        menubar.add(DisplayCurrentBalance);

        ExitProgram = new JMenu("Exit Program");
        menubar.add(ExitProgram);

        TransferAnAmountToAnotherAccount = new JMenuItem("Transer an amount to another account");
        TransferAnAmount.add(TransferAnAmountToAnotherAccount);

        ShowList = new JMenuItem("Show List");
        ListRecentTransactions.add(ShowList);

        ShowBalance = new JMenuItem("Show Balance");
        DisplayCurrentBalance.add(ShowBalance);
        event s = new event();
        ShowBalance.addActionListener(s);

        Exit = new JMenuItem("Exit Program");
        ExitProgram.add(Exit);
        event e = new event();
        Exit.addActionListener(e);

    }

    class event implements ActionListener  {
        public void actionPerformed3(ActionEvent s) throws IOException {
            BufferedReader in = new BufferedReader(new FileReader("shop-account"));
            String line;
            while((line = in.readLine()) != null)
            {
                System.out.println(line);
            }
        }
        public void actionPerformed4(ActionEvent e) {
            System.exit(0);

        }

    }

    public void displayGui() {
        MyFrame gui = new MyFrame();
        gui.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        gui.setSize(600, 300);
        gui.setVisible(true);

    }

}
}

我的代码中出现此行错误；

    }

    class event implements ActionListener  { // <<< This line
        public void actionPerformed3(ActionEvent s) throws IOException {
            BufferedReader in = new BufferedReader(new FileReader("shop-account"));
            String line;
            while((line = in.readLine()) != null)
            {
                System.out.println(line);
            }
        }
        public void actionPerformed4(ActionEvent e) {
            System.exit(0);

        }

    }

给出的错误是；

Exception in thread "AWT-EventQueue-0" java.lang.Error: Unresolved compilation problem: 
    The type Assignment4Test.MyFrame.event must implement the inherited abstract method ActionListener.actionPerformed(ActionEvent)

我不确定错误是什么或如何修复它。

感谢任何帮助，谢谢。

Answer 1

ActionListener 接口(interface)包含方法 actionPerformed，因此当您实现该接口(interface)时，必须重写 actionPerformed 方法。该方法的正确定义是:

public void actionPerformed(ActionEvent e) 

不确定这是否只是一个拼写错误，但您有两个方法 actionPerformed3 和 actionPerformed4，它们实际上并未覆盖 ActionListener 类 actionPerformed 方法。

为了避免此类问题，在您尝试覆盖的方法之上使用 @Override 注释总是有帮助的。所以这样更好、更安全:

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