泛型问题:clone()尝试分配较弱的访问权限

Question

让我们有这个类结构:

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);
   }
}

我有这样的编译错误(虽然IDE,的IntelliJ于我而言,是无法显示,而编码错误)

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

我知道编译器试图从而不是调用clone()方法,但我不明白为什么.我也试过它转换为(我认为编译器会知道在这种情况下调用哪个方法,但同样的问题).ObjectTypeCloneableTypeCloneableclone()

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

我有点困惑......我可以在这里做些什么来强制从TypeCloneable调用clone()吗？

谢谢你的帮助

Answer 1

这对我有用，（我猜测这是 Type & Type upperbound 语法的问题）：

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);
   }
}