Java generics name clash , has the same erasure

Question

I have superclass Foo. And a class Bar extending it.

public class Bar extends Foo 

Function in Foo:

protected void saveAll(Collection<?> many) 

Function in Bar:

public void saveAll(Collection<MyClass> stuff) {    super.saveAll(stuff); } 

Getting error :

 Name clash: The method saveAll(Collection<MyClass>) of type Bar has the same erasure as saveAll(Collection<?>) of type Foo but does not override it. 

What am I doing wrong?

Answer 1

You are overriding the saveAll method with an incompatible type. Perhaps you want to do something like:

public class Bar extends Foo<MyClass> 

Function in Foo<E>

protected void saveAll(Collection<E> many) 

and function in Bar:

public void saveAll(Collection<MyClass> stuff) {    super.saveAll(stuff); } 

Answer 2

Due to the type erasure feature of Java, the JVM will not be able to know whether it is the method that has the parametrized type MyClass or the first one that should be called.

If possible or applicable, the most commonly used pattern I've seen to avoid this is to change the class Foo to have a parametrized type as well:

public class Foo<T> {     protected void saveAll(Collection<T> many) {} } 

and then have Bar simply implement Foo for your specific type:

public class Bar extends Foo<MyClass> {     public void saveAll(Collection<MyClass> many) {         super.saveAll(many);     } }