Bug 461922

Description Marko van Dooren 2015-03-11 10:05:53 EDT

When a method from Object is "overridden" in an interface I, and that method is invoked in a default method of I on an object of type T where T is a type parameter with upperbound I, the "overriding" method in I is ignored (the type parameter is needed to trigger the bug).

The example below illustrates the problem. The default method does not compile in Eclipse. But it does compile with the JDK compiler (javac 1.8.0_31).

  public interface I {
    // Compiles with javac, but not with Eclipse
    default <T extends I> void compilesInJDKCompiler(T t) {
        t.clone();
    }
    
    I clone();
  }

Hovering over the method shows that it resolves to Object.clone() while the compiler is allowed to assume I.clone() because any class that implements I must respect I.clone() anyway. If we write the same method as a regular method of an unrelated class C, the problem disappears:

  public static class C {
    // Compiles with javac AND with Eclipse
    public <T extends I> void compilesInJDKCompiler(T t) {
        t.clone();
    }
  }

The problem also disappears when the parameter type is changed to I instead of using the type parameter of the method.

  public interface I {
    
    // Compiles with javac AND with Eclipse
    default void compilesInJDKCompiler(I t) {
        t.clone();
    }
    
    void clone();
  }

The problem also occurs for e.g. finalize() (works with javac, but no with Eclipse). I can't trigger the problem with other methods because there is nothing to specialize: they have no checked exceptions and no return type that can be changed.

It seems like the bound of T is ignored in default methods.