$ cat Foo.java
    interface Foo {
        private String jimbo() {
            return "yup";
        }
    }

    $ javap -c -private Foo
    Compiled from "Foo.java"
    interface Foo {
      private java.lang.String jimbo();
        Code:
           0: ldc           #1                  // String yup
           2: areturn
    }

and

    interface Bar {
      default boolean isAwesome() {
        return true;
      }
    }