Compare same objects in Java [duplicate]

Question

I write a little script to get pixel of an image and put it in an ArrayList, and i create a class who contains these values.

Here a parts of my code:

int arrC[] = {255, 0, 0};
Color   red = new Color(arrC),
        red2 = new Color(arrC);
if(!red.equals(red2)) System.out.print("It's not the same color !");

And the class Color:

class Color {

    private int RED;
    private int GREEN;
    private int BLUE;
    private String HEXA;

    public Color(int RGBColors[]) throws ColorException {
        if(RGBColors.length == 3) {
            for(int rgbcolor : RGBColors) {
                HEXA = String.format("#%02x%02x%02x", RGBColors[0], RGBColors[1], RGBColors[2]);
            }
        }else {
            throw new ColorException("Erreur : Number of the value incorrect. 3 excepted not: " + RGBColors.length);
        }
    }

    public Color(int hexacolor) {
        System.out.println(hexacolor);
    }

    /* Getter & Setters */

    public int getRED() {
        return this.RED;
    }

    //...

}

But i don't understand why variable red are not equals with the variable red2 even if they have the same propreties. How can do that ?

Because you did not implement equals, so it compares the reference, which is different. — tobias_k
– tobias_k, Commented Aug 15, 2016 at 22:00
You need to implement the Object.equals method (and should do the same for hashCode, if you plan to use instances e.g. within Maps), were you compare all properties. — qqilihq
– qqilihq, Commented Aug 15, 2016 at 22:01
Related: stackoverflow.com/q/27581/3182664 (and thousands of other questions) — Marco13
– Marco13, Commented Aug 15, 2016 at 22:01
Where exactly in your constructor do you set the values of red, green or blue? Why are you iterating over the 3 elements of the RGBColor array and at each iteration take every three values to recompute and overwrite some HEXA value? Is there any good reason to violate basic naming guidelines making fields look like constants? Please correct trivial mistakes in your code, which have nothing to do with equality of instances first... and then let your IDE generate the equals and hashCode for you to address the actual problem you are asking about. — Oleg Sklyar
– Oleg Sklyar, Commented Aug 15, 2016 at 22:37
@OlegSklyar You're right. I didn't even know why i do that ! Thank you. — Lemarcque
– Lemarcque, Commented Aug 17, 2016 at 23:49

AmanSinghal · Accepted Answer · 2016-08-15 22:03:44Z

0

The default equals() method on java.lang.Object compares memory addresses, which means that all objects are different from each other (only two references to the same object will return true).

So you need to override equals() and hashcode() method of the Color class for the code to work properly.

answered Aug 15, 2016 at 22:03

AmanSinghal

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UserF40 · Accepted Answer · 2016-08-15 22:00:55Z

0

You need to override and implement equals() and subsequently hashcode() in your Color class.

Something like:

@Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + BLUE;
        result = prime * result + GREEN;
        result = prime * result + ((HEXA == null) ? 0 : HEXA.hashCode());
        result = prime * result + RED;
        return result;
    }

@Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Color other = (Color) obj;
        if (BLUE != other.BLUE)
            return false;
        if (GREEN != other.GREEN)
            return false;
        if (HEXA == null) {
            if (other.HEXA != null)
                return false;
        } else if (!HEXA.equals(other.HEXA))
            return false;
        if (RED != other.RED)
            return false;
        return true;
    }

answered Aug 15, 2016 at 22:00

UserF40

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1 Comment

Lemarcque Over a year ago

Wow, thank you for use your time to help me. I better understand !

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