java - 实现Comparable接口(interface)的问题

Question

我有以下代码，是我在《Java for Everyday》一书中实现的第 9 章中实现的:

package Inheritance;

import java.util.Scanner;

interface Comparable{
    int compareTo(Object otherObject);
}

interface Measurable{
    double getMeasure();
}


public class BankAccount implements Comparable, Measurable {
    private double balance;
    private int counter;
    public String account;

    public BankAccount(){
        balance = 0;
        counter = 0;
        account = "";
    }

    public void SetAccount(String accountNumber, double amount){
        account = accountNumber;
        balance = amount;
    }

    public void Deposit(double amount){
        balance = balance + amount;
        counter = counter + 1;
        System.out.println("Account: "+ account + " has balance: " + balance);
    }

    public void Withdraw(double amount){
        balance = balance - amount;
        counter = counter + 1;
        System.out.println("Account: "+ account + " has balance: " + balance);
    }

    public double getBalance(){
        return balance;
    }

    public void MonthEnd(){
        counter = 0;
    }

    public void printMenu(){
        System.out.println("Please choose your options to proceed: ");
        System.out.println("D)eposit W)ithdraw M)onth end Q)uit");
    }

    public double getMeasure(){
        return balance;
    }

    public int compareTo(Object otherObject) {
        BankAccount other = (BankAccount) otherObject;
        if (balance < other.balance) {
            return -1;
        }
        if (balance > other.balance) {
            return 1;
        }
        return 0;
    }

然后我按如下方式运行它:

public class Implementation {

    public static void main(String[] args) {

        //Implement Comparable Interface example
        BankAccount[] accounts2 = new BankAccount[3];
        accounts2[0] = new BankAccount();
        accounts2[0].SetAccount("SA001", 10000);
        accounts2[1] = new BankAccount();
        accounts2[1].SetAccount("SA001", 5000);
        accounts2[2] = new BankAccount();
        accounts2[2].SetAccount("SA001", 20000);
        System.out.println(accounts2[0].compareTo(accounts2[1]));

        Arrays.sort(accounts2);
    }
}

但是，它在我的 Comparable 界面上给了我以下错误。我已经在 BankAccount 类中提供了compareTo 方法，为什么它不起作用？

线程“main”中的异常 java.lang.ClassCastException:类 Inheritance.BankAccount 无法转换为类 java.lang.Comparable(Inheritance.BankAccount 位于加载程序“app”的未命名模块中； java.lang.Comparable 位于加载程序“bootstrap”的 java.base 模块中) 在 java.base/java.util.ComparableTimSort.countRunAndMakeAscending(ComparableTimSort.java:320)

at java.base/java.util.ComparableTimSort.sort(ComparableTimSort.java:188)

at java.base/java.util.Arrays.sort(Arrays.java:1250)

at Inheritance.Implementation.main(Implementation.jav

Answer 1

摆脱:

interface Comparable{
    int compareTo(Object otherObject);
}

因为您通过创建自己的接口(interface)来掩盖同名的核心 Java 接口(interface)，从而使编译器感到困惑。。相反，请使用核心 Java Comparable 接口(interface)。

这里的问题是 Arrays.sort(...) 方法必须使用核心接口(interface)，而不是您自己的接口(interface)。否则，您的代码可能可能会工作，尽管可能会让其他编码人员感到困惑，更重要的是您 future 的自己。

旁注，我建议使用该界面的通用版本。我还喜欢总是在我认为可能覆盖的任何方法上方添加@Override注释，以便编译器对其进行测试我并在编译时警告我:

public class BankAccount implements Comparable<BankAccount>, Measurable {

    @Override
    public int compareTo(BankAccount other) {
        // ....
    }