equals方法 - 如何覆盖

Question

我需要帮助来覆盖该equals方法.除了这个equals方法,我的一切都在工作.equals我目前拥有的方法并没有给我正确的答案.我似乎无法弄清楚可能是什么问题.

我的课:

package myclasses;

public class Currency
{
    private int dollars, cents;

    public Currency()
    {
        dollars = 0;
        cents = 0;
    }

    public Currency(int d, int c)
    {
        this.dollars = d;
        this.cents = c;

        setCents(cents);
    }

    public int getDollars()
    {
        return dollars;
    }

    public int getCents()
    {
        return cents;
    }

    private void setDollars(int dollars)
    {
        this.dollars = dollars;
    }

    private void setCents(int cents)
    {       
        while(cents > 99)
        {
            cents = (cents - 100);
            dollars++;
        }

        this.cents = cents;
    }

    public void setAmount(int newDollars, int newCents)
    {
        setDollars(dollars);
        setCents(cents);
    }

    public void add(int dollars, int cents)
    {
        this.dollars =  dollars + getDollars();
        cents = cents + getCents();

        setCents(cents);
    }

    public boolean equals(Object dollars, Object cents)
    {
        if(this == dollars && this == cents)
            return true;

        if(!(dollars instanceof Currency) || !(cents instanceof Currency))
            return false;

        Currency money = (Currency) dollars;
        Currency penny = (Currency) cents;

        return (this.dollars == money.dollars) && (this.cents == penny.cents);
        //return Currency.dollars.equals(Currency.cents);
        //return this.equals(dollars) && this.equals(cents);

    }

    public boolean isZero()
    {
        if(getDollars() == 0 && getCents() == 0)
        {
            return true;
        }
        return false;
    }

    public String toString()
    {
        return "$" + getDollars() + "."   +
                (getCents() < 10 ? ("0" + getCents()) : getCents());
    }
}

Answer 1

您的equals()方法有一些错误,如:

if(this == dollars && this == cents)

这永远不会是真的......这必须是:

if(this.dollars == dollars && this.cents == cents)

但我不会在编码等于中做任何努力,建议自动生成等于.像这样的东西:

@Override
public boolean equals(Object obj) {
    if (this == obj)
        return true;
    if (obj == null)
        return false;
    if (getClass() != obj.getClass())
        return false;
    Currency other = (Currency) obj;
    if (cents != other.cents)
        return false;
    if (dollars != other.dollars)
        return false;
    return true;
}

也强烈建议,(几乎是无法避免的@AdriaanKoster评论)当你重写equals()方法,还覆盖hashCode()
在equals()定义:

请注意,通常需要在重写此方法时覆盖hashCode方法,以便维护hashCode方法的常规协定,该方法声明相等对象必须具有相等的哈希代码.

哈希码:

@Override
public int hashCode() {
    final int prime = 31;
    int result = 1;
    result = prime * result + cents;
    result = prime * result + dollars;
    return result;
}