CODEWITHSUNDEEP
java
user1210233
user1210233

Reputation: 2940

HashSet contains() returns false for custom object. hashCode() and equals() seem to be implemented correctly

I have the following simple Rectangle class. If two rectangles have the same height and width, they are equal and have the same hashcode. I added a new rectangle to a hashSet.

Set<Rectangle> set = new HashSet<Rectangle>();
set.add(new Rectangle(3,3));

When I try to call contains on a new rectangle with same height and width, it returns false.

set.contains(new Rectangle(3,3)) returns false. I can't figure out why. Any ideas?

   public class Rectangle implements Comparable<Rectangle> {
            final int height, width, area, minimumEdge, maximumEdge;

            public Rectangle(int height, int width) {
                this.height = height;
                this.width = width;
                area = height * width;
                maximumEdge = height > width ? height : width;
                minimumEdge = height < width ? height : width;
            }

            public int compareTo(Rectangle rect2) {
                if (rect2.minimumEdge > this.minimumEdge) {
                    return -1;
                } else if (rect2.minimumEdge < this.minimumEdge) {
                    return 1;
                } else {
                    return 0;
                }
            }

            public int hashCode(){
                return ((width + height)*31);
            }

            public boolean equals(Rectangle rect2){
                return (this.height == rect2.height && this.width == rect2.width);
            }
        }

Upvotes: 3

Views: 2575

Answers (2)

alhimik45
alhimik45

Reputation: 92

Here:

public boolean equals(Rectangle rect2){
            return (this.height == rect2.height && this.width == rect2.width);
        }

You make your own equals method, not override superclass method.

You must write like:

@Override
public boolean equals(Object obj) {
    if (this == obj)
        return true;
    if (obj == null)
        return false;
    if (getClass() != obj.getClass())
        return false;
    Rectangle rect2 = (Rectangle) obj;
    return (this.height == rect2.height && this.width == rect2.width);
}

Upvotes: 3

SLaks
SLaks

Reputation: 888223

You haven't actually overridden equals().

You created a new equals(Rectangle) method, which has nothing to do with the virtual equals(Object) method.

This is why you should always add @Override when trying to override methods.

Upvotes: 14

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