Generic issue: clone () tries to assign weaker permissions

Question

Let this class structure:

public interface TypeIdentifiable {} public interface TypeCloneable extends Cloneable { public Object clone() throws CloneNotSupportedException; } public class Foo implements TypeCloneable, TypeIdentifiable { @Override public Object clone() throws CloneNotSupportedException { // ... return null; } } public abstract class AbstractClass<T extends TypeCloneable & TypeIdentifiable> { public void foo(T element) throws Exception { TypeCloneable cloned = (TypeCloneable) element.clone(); System.out.println(cloned); } } 

I have this compilation error (although the IDE, Intellij in my case, cannot show an encoding error)

 Error:(4, 37) java: clone() in java.lang.Object cannot implement clone() in foo.TypeCloneable attempting to assign weaker access privileges; was public 

I know that the compiler is trying to call the clone() method from Object instead of TypeCloneable , but I don't understand why. I also tried casting it to TypeCloneable (I assumed that the compiler knows which clone() method calls in this case, but the same problem).

  public void foo(T element) throws Exception { TypeCloneable typeCloneable = (TypeCloneable) element; TypeCloneable cloned = (TypeCloneable) typeCloneable.clone(); } 

I'm a little confused ... Can I do something here to force callling clone () from TypeCloneable?

Thanks for the adpp

Answer 1

This works for me (I assume this is a problem with the syntax of the top and top types):

 interface TypeIdentifiable {} interface TypeCloneable extends Cloneable { public Object clone() throws CloneNotSupportedException; } class Foo implements TypeCloneable, TypeIdentifiable { @Override public Object clone() throws CloneNotSupportedException { // ... return null; } } interface TypeCloneableAndIndetifiable extends TypeCloneable, TypeIdentifiable { } abstract class AbstractClass<T extends TypeCloneableAndIndetifiable> { public void foo(T element) throws Exception { TypeCloneable cloned = (TypeCloneable) element.clone(); System.out.println(cloned); } }