JAVA class and object ------ inheritance, java ------ inheritance

JAVA class and object ------ inheritance, java ------ inheritance

Understanding: inheritance can be understood as an object's process of obtaining attributes. If Class A is the parent class of Class B, and Class B is the parent class of class C, we also say that C is A subclass of Class A, and class C is inherited from Class. In java, class inheritance is a single inheritance, that is, a subclass can only have one parent class.

Keywords: extends and implements.

The use of these two keywords determines whether an object is a IS-A (a) relationship with another object.

Example:

// A.javapublic class A {    private int i;    protected int j;     public void func() {     }} // B.javapublic class B extends A {}

Note: In the preceding example, B is inherited by A, and B is A subclass of. As A subclass, B's instance has all the member variables of A, but has no access permission to private member B, which guarantees the encapsulation of.

 

IS-A relationships: one object is another object category! We can determine the Mammal IS-A Animal by using the instanceof operator.

class Animal{}class Dog extends Animal{}class Cat extends Animal{}class Pig extends Animal{}public class AnimalTest{    public static void main(String args[]){        Dog dog=new Dog();        Cat cat=new Cat();        Pig pig=new Pig();        System.out.println(dog instanceof Animal);        System.out.println(cat instanceof Animal);        System.out.println(pig instanceof Animal);    }}

 

Let's take a look.ImplementsHow the keyword is used to represent the IS-A relationship.

ImplementsKeywords cannot be used in this case when the class inheritance interface is used.Extends.

interface Animal{}class Mammal implements Animal{}class Dog implements Animal{}public class AnimalTestTwo {   public static void main(String args[]){      Mammal m = new Mammal();      Dog d = new Dog();      System.out.println(m instanceof Animal);      System.out.println(d instanceof Animal);   }} 

 

 

Java only supports single inheritance (inheriting basic classes and abstract classes), but we can use interfaces (implementing multiple inheritance interfaces). The script structure is as follows:

Public class Apple extends Fruit implements Fruit1, Fruit2 {}
Generally, we use the extends keyword to inherit basic classes and abstract classes, and use the implements keyword to inherit interface classes.