this Key words and super What do the keywords stand for ? And their respective scenarios and roles .

this: References to the current object , It exists inside the ordinary member method

effect ：

• Used inside the normal member method of a class
• Use format as this. Member variables ,this. Member method
• this Reference representing the current object

super： Identification of the parent storage space （ Reference to the current parent object ）

Usage scenarios and differences

• Member variables ：

  • this. Variable Member variables in this class
  • super. Variable Member variables in the parent class

  class Animal {
  
  String name;
  public Animal() {
  
  }
  public Animal(String name) {
  
  this.name = name;
  }
  public void showName() {
  
  }
  }
  class Dog extends Animal {
  
  public Dog() {
  
  }
  public Dog(String name) {
  
  super(name);
  }
  public void showName() {
  
  System.out.println(super.name);
  }
  }
  

• Construction method ：

  • this(…) The construction method in this class
  • super(…) The construction method in the parent class

  class Animal {
  
  String name;
  int age;
  public Animal(String name) {
  
  this(name,1);
  }
  public Animal(String name,int age) {
  
  this.name = name;
  this.age=age;
  }
  public void showName() {
  
  }
  }
  class Dog extends Animal {
  
  public Dog(String name) {
  
  super(name);
  }
  public Dog(String name,int age) {
  
  super(name,age);
  }
  public void showName() {
  
  System.out.println(super.name);
  System.out.println(this.age);
  }
  }
  

• Member method ：

  • this. Method name () Member methods in this class
  • super. Method name () Member methods in the parent class

  class Animal {
  
  String name;
  int age;
  public Animal(String name) {
  
  this(name,1);
  }
  public Animal(String name,int age) {
  
  this.name = name;
  this.age=age;
  }
  public void showName() {
  
  System.out.println(" Parent class showName() Method ");
  }
  }
  class Dog extends Animal {
  
  public Dog(String name) {
  
  super(name);
  }
  public Dog(String name,int age) {
  
  super(name,age);
  }
  public void showName() {
  
  super.showName();
  System.out.println(super.name);
  this.showAge();
  }
  public void showAge() {
  
  System.out.println(this.age);
  }
  }
  

  this and super Description of the difference between

  1. When a member variable and a local variable have the same name , have access to this To distinguish between .
  2. this Can be used in constructors , Call other constructors （ It can only be defined in the first line , Initialization must be executed ）.super can Call the parent class directly 、 Method 、 Construction method . But when you call the constructor , You can’t use both at the same time .
  3. super() Call parent constructor from subclass ,this() Call other methods in the same class .
  4. this and super Cannot appear in a constructor at the same time .
  5. super() and this() Must be placed in the first line of the construction method .
  6. this and super Are all objects , So no more static Use in the environment .