CODEWITHSUNDEEP
javaequals
user1738871
user1738871

Reputation: 9

equals method not returning expected o/p

Please solve my doubt about equals(). I think equlas() checks content so in following example it should print true because content is same of both t1 and t2, But it prints false. Why?

public class Test {
        public static void main(String args[]) {
                Test1 t1 = new Test1(10);
                Test1 t2 = new Test1(10);
                System.out.println(t1.equals(t2));
        }
}

class Test1 {
        int a ;
        Test1( int x){
                a = x ;
        }
}

Thanks in advance

Upvotes: 0

Views: 138

Answers (5)

arshajii
arshajii

Reputation: 129477

equals() by default compares references; and the references of two different objects (in this case t1 and t2) are unequal. You have to override it to check for equality between members:

@Override
public boolean equals(Object o) {
    return (o instanceof Test1) && a == ((Test1)o).a;
}

As a general rule, it's a good idea to override hashCode() whenever you override equals():

@Override
public int hashCode() {
    return a;
}

Upvotes: 2

Narendra Pathai
Narendra Pathai

Reputation: 41935

@Override
public boolean equals(Object obj){

    if(!(obj instanceof Test))
         return false;

    return ((Test)obj).x == this.x;
}

Override equals() in Test to check value of x

Upvotes: 0

user2110286
user2110286

Reputation:

You should override equals() because default method compares the references.

The method below will compare two objects correctly.

public boolean equals(Object obj) {
            if (this == obj)
                return true;
            if (obj == null)
                return false;
            if (getClass() != obj.getClass())
                return false;
            Test1 other = (Test1) obj;
            if (a != other.a)
                return false;
            return true;
}

Upvotes: 2

Juned Ahsan
Juned Ahsan

Reputation: 68715

You need to override the equals method in your Test1 class. Maybe something like this:

public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Test1 other = (Test1) obj;
        if (a != other.a)
            return false;
        return true;
    }

Upvotes: 1

rgettman
rgettman

Reputation: 178243

You need to override equals in your Test1 class to get the desired behavior. Otherwise, the class will inherit equals from Object, which only determines if the two references refer to the same object. Here, you have different instances, so false is the result.

Quoting from the linked javadocs:

The equals method for class Object implements the most discriminating possible equivalence relation on objects; that is, for any non-null reference values x and y, this method returns true if and only if x and y refer to the same object (x == y has the value true).

Typically you test if the other object is of the same class, then you compare the individual field(s) for equality.

Upvotes: 2

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