I can't understand relationship between superclass, interface and child class if I use the same name methods in both interface and abstract class

Question

public interface Pet { // Pet Interface
    default void introduce() {
        System.out.println("Interface");
    } 
}

abstract public class Animal {
    public void introduce() {
        System.out.println("Animal class");
    }
}

public class Dog extends Animal implements Pet{}

Now when I called the introduce method on Dog, what actually happens?

Answer 1

default methods are always 'last in line'. If any method anywhere in the hierarchy of the chain of classes (so, here, 'Dog' at the top, then Animal, then Object - those are the classes involved in the hierarchy) matches, that always wins.

Only if zero methods are found in the entire class chain, and the interface chain contains exactly 1 method with a default implementation - then that one is chosen instead. If there are more than one, then your code won't compile (if you have class A implements B, C {} and both B and C have the same method defined and both have a default impl, then you can't compile A without explicitly writing that method into A.