Overview of default methods conflicts.

• super class with interface conflict

  • base class

    class CustomClass extends SuperClass implements Interface1 {}
    

  • super class

    class SuperClass {
        public String get() {
            return "SuperClass";
        }
    }
    

  • interface

    interface Interface1 {
        default String get() {
            return "Interface1";
        }
    }
    

  then if you call method get() on an instance of CustomClass it will be called method from SuperClass:

  assertThat(new CustomClass().get(), is("SuperClass"));
  

  Note that If we narrow scope of get() method in superclass

  class SuperClass {
      String get() {
          return "SuperClass";
      }
  }
  

  we obtain compile time error under

  class CustomClass extends SuperClass implements Interface1 {}
  

• interface with other interface conflict - compile time error