Why does the Java compiler add bridge-visibility methods for public methods defined in super-types of packages?

Question

I am wondering why the Java compiler will add a bridge method for the method foohere:

public class Outer {

  class SuperClass {
    public void foo() { }
  }

  public class SubClass extends SuperClass { }
}

The method is foocompiled as publicin a type SuperClass. However, a method SubClassredefines a method as a bridge to the same method. I wonder why this bridge is needed.

Answer 1

Rationally adding this bridge method is the cornerstone of the Java reflection API, which calls IllegalAccessExceptionwithout adding the bridge method. The error is described here in the Oracle bug tracker :

Reflective challenge

Subclass.class.getMethod("foo").invoke(new Subclass())

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