实现可比接口的问题

2024-05-20 • 问答

我有以下代码可以在“ Java for Everyone”一书的第9章中实现：

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;
    }

然后按如下所示运行它：

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);
    }
}

但是我的Comparable接口给了我以下错误。我已经在Bankaccount类中提供了compareTo方法，为什么它不起作用？

线程“主”中的异常java.lang.ClassCastException：类Inheritance.Bankaccount无法转换为类java.lang.Comparable（Inheritance.Bankaccount在加载程序“ app”的未命名模块中； java.lang.Comparable在加载程序'bootstrap'的模块java.base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

摆脱：

interface Comparable{
    int compareTo(Object otherObject);
}

由于您通过创建自己的接口来掩盖核心Java接口同名，从而混淆了编译器。而是使用核心Java Comparable接口。

这里的问题是Arrays.sort(...)方法必须使用核心接口，而不是您自己的接口。否则，您的代码可能可能起作用，尽管这可能会使其他编码人员感到困惑，更重要的是您的未来自我。

旁注，我建议使用接口的通用版本。我还想总是在我认为可能被覆盖的任何方法上方添加@Override批注，以便编译器会为我测试并警告我在编译时：

public class BankAccount implements Comparable<BankAccount>,Measurable {

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

要使Arrays.sort（accounts2）函数正常工作，您的BankAccount类必须实现jdk本身提供的Comaparable接口-java.lang.Comparable。不是您创建的那个。

从您的BankAccount类中删除以下代码。这会起作用。

interface Comparable{
int compareTo(Object otherObject);

}

实现可比接口的问题

windger2008 回答：实现可比接口的问题

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