Java – generics – method return type as extension class

I tried to do this in Java 6:

abstract class CurrClass{
    public <T extends CurrClass> T setField (String str) {
        return this;
    }
}

Compiler complaint error: type mismatch: cannot convert from currclass to t

Add an actor's work and issue a warning: "return (T) this;"

Is there a clearer grammar to do this? Why do actors need?

Solution

The return type is more restrictive than the returned object This is why the compiler generates errors (and subsequent warnings) Consider this:

class A extends CurrClass {}
class B extends CurrClass {}

...

A myObject = new B().setField("stringhere");

This is perfectly legal in your settings, but will result in ClassCastException

This is why we usually return only types that are more stringent than signature requirements