I have a class that accepts a generic type, and I want to override the equals method in a non-awkward way (i.e. something that looks clean and has minimal amount of code, but for a very general use case).

Right now I have something like this:

public class SingularNode {

private T value;

@SuppressWarnings(“unchecked”)

@Override

public boolean equals(Object other){

if(other instanceof SingularNode>){

if(((SingularNode)other).value.equals(value)){

return true;

}

}

return false;

}

}

Which, I’m guessing, is pretty flawed – I’m doing a cast to SingularNode on the other object, which could potentially throw an error.

Another thing is – when I do if(other instanceof SingularNode>) I’m actually not checking exactly the right thing. I actually want to check against type T and not type ?. Whenever I try to make the ? into T, I get some error like:

Cannot perform instanceof check against parameterized type SingularNode. Use the form SingularNode> instead, since further generic type information will be erased at runtime

How can I get around this? Is there some way to do T.class.isInstance(other); ?

I suppose there’s one really ugly hack solution like this:

@SuppressWarnings(“unchecked”)

public boolean isEqualTo(Class> c, Object obj){

if(c.isInstance(obj) && c.isInstance(this)){

if(((SingularNode)obj).value.equals(value)){

return true;

}

}

return false;

}

But that just looks really awkward with the extra method parameter, and it’s also not a built-in function like equals is.

Any one who understand generics please explain this? I’m not that proficient with Java, as you can clearly see, so please explain with a tad bit more detail!

解决方案

This version gives no warnings

public boolean equals(Object other){

if (other instanceof SingularNode>){

if ( ((SingularNode>)other).value.equals(value) ){

return true;

}

}

return false;

}

As for casting to SingularNode it does not help anything, you cannot assume that T can be anything but Object.

Learn more about how generics are compiled in Java at