Set Contains method is not working correctly after overriding equals() and hashcode() methods

Question

I have created one class name like Test and have overriden its equals() and hashcode() methods and then created its 2 objects like below -

Test obj1 = new Test ();
Test obj2 = new Test ();

and now performaing following operation -

obj1.equals(obj2); // I am getting **True** that is fine.

But if i change i code bit like below -

Set<Test> testSet = new Set<Test>();
testSet.add(obj1);

Print : testSet.contains(obj2); // It is returning **False**....

I debug the code and found in this case HashCode() method is getting called but equals() is not being called. HashCode is some for both the object.

As per my understanding it should return True.

Modified --

My code is below -

Class

     public Class DMAClipLevelWrapperForExport {
        public String businessUnit {get; set;}
        public String dmaType {get; set;}
        public Decimal tcvMin {get; set;}
        public Decimal tcvMax {get; set;}        

        /*
         * Overriding equals
         */     
        public Boolean equals(DMAClipLevelWrapperForExport obj) { 
            if(obj != null){
                if(obj.tcvMin == this.tcvMin && obj.tcvMax == this.tcvMax) {
                    return true;
                } else {
                    return false;
                }
            } else {
                return false;
            }           
        }

        /*
         * Overriding hashCode
         */ 
        public Integer hashCode() {
            return this.tcvMin.intValue() + this.tcvMax.intValue();
        }
     }

---

Code written to test

        Set<DMAClipLevelWrapperForExport> dmaClipLevelWrapperForExport = new Set<DMAClipLevelWrapperForExport>();

        DMAClipLevelWrapperForExport one = new DMAClipLevelWrapperForExport();
        one.businessUnit = 'APACC';
        one.dmaType = 'CES';
    one.tcvMin = 0;
        one.tcvMax = 500000;
    dmaClipLevelWrapperForExport.add(one);

        DMAClipLevelWrapperForExport clipLevel = new DMAClipLevelWrapperForExport();
        clipLevel.businessUnit = 'APACC';
        clipLevel.dmaType = 'CES';
        clipLevel.tcvMin = 0;
        clipLevel.tcvMax = 500000;


    if(dmaClipLevelWrapperForExport.contains(clipLevel)) {
            system.assert(false, 'Object found in list');
        } else {
            system.assert(false, 'Object not found in list');
        }

Always getting 'Object not found in list'.

Can anyone explain what is wrong in this code please?

Thanks for reply

Answer 1

The issue is that you have not used the correct method signature for overriding equals.

Your method signature is:

public Boolean equals(DMAClipLevelWrapperForExport)

The correct one to use is covered in the Using Custom Types in Map Keys and Sets documentation.

Adding equals and hashCode Methods to Your Class

To ensure that map keys of your custom type are compared correctly and their uniqueness can be determined consistently, provide an implementation of the following two methods in your class:

The equals method with this signature:

public Boolean equals(Object obj) {
     // Your implementation
}

The hashCode method with this signature:

public Integer hashCode() {
    // Your implementation
}

Changing your equals method to following gives me the correct results using the test method that you provided.

public Boolean equals(object obj) 
{ 
    if(obj != null && obj instanceof DMAClipLevelWrapperForExport)
    { 
        DMAClipLevelWrapperForExport dma = (DMAClipLevelWrapperForExport)obj;

        if(dma.tcvMin == this.tcvMin && dma.tcvMax == this.tcvMax) 
        {
            return true;
        } 
        else 
        {
            return false;
        }
    } 
    else 
    {
        return false;
    }           
}

Answer 2

It appears you may have a typo in your code; you are making a Set<Test> instead of a Set<Text>, which is somehow working in this case (probably because you have a class named Test that is for some reason compatible with Text).

I made an example class that shows why it's important to make sure you're using hashcode and equals correctly, showing how you can create absurd results:

public class Example {
    virtual class Generic {
        virtual integer hashCode() {
            return 0;
        }
        virtual boolean equals(object o) {
            return true;
        }
    }

    class Singleton extends Generic {
    }

    class Multiton extends Generic {
        override integer hashCode() {
            return Crypto.getRandomInteger();
        }
        override boolean equals(object o) {
            return false;
        }
    }

    public static void doExample() {
        Set<Generic> single = new Set<Generic>(), single2 = new Set<Generic>(), multi = new Set<Generic>();
        Singleton a = new Singleton(), b = new Singleton();
        Multiton c = new Multiton();

        single.add(a);
        single.add(b);

        single2.add(a);

        multi.add(c);
        multi.add(c);

        System.assertEquals(1, single.size());
        System.assertEquals(true, single.contains(a));
        System.assertEquals(true, single.contains(b));
        System.assertEquals(true, single.contains(new Singleton()));
        System.assertEquals(false, single.contains(c));
        System.assertEquals(2, multi.size());
        System.assertEquals(false, multi.contains(c));
        System.assertEquals(1, single2.size());
        System.assertEquals(true, single2.contains(a));
        System.assertEquals(true, single2.contains(b));
    }
}

Note here how I add two singletons to a set, yet the size remains 1, and any singleton I pass in matches any other existing singleton. Not that this isn't actually a singleton, since we are able to create multiple objects, but this shows how a set of misbehaving functions can return odd results.

Next, I add the same Multiton to the set twice, and it results in a size of 2 in the set, and yet contains returns false when I ask the set to confirm if c is present. There's a minuscule chance this code will fail, less than that of being struck by lightning or winning the lottery.

The Singleton class demonstrates that your code should indeed return true if written correctly. I only provided the opposite example to show how the same object could not appear in a set.