Enthuware

Please explain how option three satisfies the equals contract. I am confused

Can you show me a situation where it breaks the contract?

I thought option 3 would always return false because I thought "this" would be of reference type, TestClass. As this and tc refer to different class types, this == tc should always return false.

Why is this not the case?

Why do you think this and tc will always refer to objects of different classes?

admin wrote:Why do you think this and tc will always refer to objects of different classes?

I suppose I am thinking that 2 reference variables (an object reference and a TestClass reference) can not be deemed equal as they are different types but I suppose it is the object that they point to that is compared and they can (via polymorphism?) point to the same object.

Yes, two references can point to the same object. For example:
TestClass t = new TestClass();
Object o = t; //now, o and t both point to the same TestClass object.
If you pass o to the equals method, it should return true.

public boolean equals(Object tc) {    return this == tc; }

More than valid this seems to be useless since it seems to be the implementation already present in Object class.
Maybe the last option is a better choice? Can we consider valid a method with such override?

I agree it is useless but it is still valid, which is what this question cares about.