The currently-specified behavior of resolution is that a private class method takes priority over an interface method. (This is a problem -- see JDK-8021581.)

When default methods are involved, this rule is not being followed, and there are some inconsistencies.

Example 1 is the expected behavior for all 3 cases.

There may be some similar inconsistencies when package-access methods are involved.

-----
Example 1 (no default):

public class A {
 private void m() { System.out.println("A.m"); }
 public static void main(String... args) { B b = new C(); b.m(); }
}

public interface I {
 public void m();
}

public abstract class B extends A implements I {
}

public class C extends B {
 public void m() { System.out.println("C.m"); }
}

public class Test {
 public static void main(String... args) { B b = new C(); b.m(); }
}

java Test
Exception in thread "main" java.lang.IllegalAccessError: tried to access method A.m()V from class Test

java A
A.m

-----
Example 2 (default, overridden):

public class A {
 private void m() { System.out.println("A.m"); }
 public static void main(String... args) { B b = new C(); b.m(); }
}

public interface I {
 public default void m() { System.out.println("I.m"); }
}

public abstract class B extends A implements I {
}

public class C extends B {
  public void m() { System.out.println("C.m"); }
}

public class Test {
 public static void main(String... args) { B b = new C(); b.m(); }
}

java Test
C.m

java A
C.m

-----
Example 3 (default, not overridden):

public class A {
 private void m() { System.out.println("A.m"); }
 public static void main(String... args) { B b = new C(); b.m(); }
}

public interface I {
 public default void m() { System.out.println("I.m"); }
}

public abstract class B extends A implements I {
}

public class C extends B {
}

public class Test {
 public static void main(String... args) { B b = new C(); b.m(); }
}

java Test
Exception in thread "main" java.lang.IllegalAccessError: tried to access method A.m()V from class B

java A
Exception in thread "main" java.lang.IllegalAccessError: tried to access method A.m()V from class B