Why are there "two abstract methods" in the functional interface comparator?

In these two days, I found that Comparator There is “ Two abstract methods ”, namely compare and equals. This makes me very confused , Isn't a functional interface only an abstract method ？（ The specific methods 、default Methods are not included ）

Until we see @FunctionalInterface Of JDK Documentation Comments To solve my doubts .

• If the abstract method declared in an interface overrides the superclass Object Any one of the classes public Method , Then these abstract methods will not be included in the number of abstract methods of the interface . Because the implementation of any interface will be from its parent class Object Or get implementations of these methods elsewhere .

  • The interface also inherits Object, So define in the interface equals The method is essentially right Object Rewriting of （ Abstract rewrites concrete ）.
  • If a class inherits its parent class at the same time , And implement the interface , And they have the same name method , Use Superclass priority

  

/** * @Author: posper * @Date: 2022/07/20 15:49 */
public class Test {
    
	public static void main(String[] args) {
    
		Animal dog = new Dog();
		//  Superclass priority , So what is called here is the parent class  Animal  Medium  run()  Method 
		dog.run();
	}
}

//  verification “ Super class priority principle ”, see  main()  in  dog.run()  Method .
class Dog extends Animal implements Run {
    
	int age;
	String name;
}

//  Interface 
@FunctionalInterface
interface Run {
    
	void run();

	//  Here's an analogy  Comparator  Medium  equals,`@FunctionalInterface`  It will not be regarded as an abstract method 
	@Override
	boolean equals(Object o);
}

//  Parent class 
class Animal {
    
	public void run() {
    
		System.out.println(" call Animal Of run() Method ");
	}
}

//  verification “ Abstract rewrites concrete ”
abstract class Cat extends Animal {
    
	//  Abstract rewrites concrete methods , Yes, but it doesn't feel necessary ...
	@Override
	public abstract void run();
}

Running results ：