Equals method - how to override

Question

I need help to override the method equals. Everything works for me, except for the method equals. The method equalsthat I have does not give me the correct answer. I can’t understand what could be the problem.

My class:

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

There equals()are some errors in your method , for example:

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

It will never be true ... it should be:

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

But I will not make any efforts to code peers, it is recommended to auto-generate peers. Something like that:

@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;
}

( , @AdriaanKoster), equals(), hashCode()
equals() :

, hashCode , , hashCode, , -.

-:

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

Answer 2

, equals. , equals

public boolean equals(Object obj) {
    if (this == obj) {
        return true;
    } else if (obj == null) {
        return false;
    } else if (getClass() != obj.getClass()) {
        return false;
    }

    //a cast of object to the class you are using should be here
    if (this.someField.equals(castObject.someField)
            && this.otherField.equals(castObject.otherField)) {
        return true;
    }

    return false;
}

, . - , , , , , . , , , 3 .

, obj , . - , -

else if (getClass() != obj.getClass()) {
    return false;
} 

, , . , , . , .

Answer 3

equals, equals.

use the code below to redefine equals instead -

public boolean equals(Object currency) {

Currency newref = null;

if (currency instanceof Currency) {
  newref = (Currency)currency;
}
return (this.dollars == newref.dollars) && (this.cents == newref.cents);
}