Object-oriented abstraction (abstract)

Object-oriented abstraction (abstract)

An overview of abstract classes

• A: Overview of abstract classes
  
  • abstraction is incomprehensible
• B: abstract class features
  
  • a: Abstract classes and abstract methods must be modified with the abstract keyword
    
    • abstract class class name{}
    • public abstract void eat();
  • b: An abstract class does not necessarily have an abstract method, and a class with an abstract method must be an abstract class or an interface
  • c: Abstract classes cannot be instantiated So, how can abstract classes be instantiated?
    
    • In a polymorphic manner, instantiated by a concrete subclass. In fact, this is also a kind of polymorphism, abstract class polymorphism.
  • d: subclass of abstract class
    
    • Either an abstract class
    • Either override all abstract methods in abstract class
• C: Case Demonstration
  
  • Abstract class features

Features of abstract class members

• A: Member characteristics of abstract classes
  
  • a: member variable: either a variable or a constant. Can abstract modify member variables? Cannot modify member variables
  • b: Construction method: Yes.
    
    • Initialization for subclasses to access parent class data.
  • c: member method: can be either abstract or non-abstract.
• B: Case Demonstration
  
  • Member characteristics of abstract classes
• C: Member method characteristics of abstract classes:
  
  • a: An abstract method enforces something that subclasses do.
  • b: Non-abstract method subclass inheritance, improve code reuse.

Sunflower Collection of Abstract Classes

public class Test_葵花宝典 {

public static void main(String[] args) {
    岳不群  小岳子 = new 岳不群();
    小岳子.自宫();

}

}
abstract class 葵花宝典{  //可以了理解为 葵花宝典是抽象的武功
public abstract void 自宫();  //想要练成葵花宝典  必须自宫，由于自宫方法很多所以用到抽象方法
}

class 岳不群 extends 葵花宝典{
public void 自宫(){
    System.out.println("用牙签");
}   
}

class 林平之 extends 葵花宝典{
public void 自宫(){
    System.out.println("用指甲刀");
}
}

abstract cat and dog

• Specific things: cats, dogs

  • Commonalities: name, age, meals
  • Cat's Trait: Catches mice
  • Dog Traits: Housekeeping

  public class Text_2{

  public static void main(String[] args) {
  
  Cat c = new Cat("加菲",8);
  System.out.println(c.getName()+ "..." + c.getAge());
  c.eat();
  c.catchMousr();
  
  Dog d = new Dog("八公",30);
  System.out.println(d.getName() + "..." + d.getAge());
  d.eat();
  d.lookHome();
  }
  }
  
  abstract class Animal{
  private String name;
  private int age;
  
  
  public Animal(){}
  
  public Animal(String name,int age){
      this.name = name;
      this.age = age;
  }
  public void setName(String name){ //设置姓名
      this.name =name;
  }
  public String getName(){   // 获取姓名
      return name;
  }
  public void setAge(int age){ //设置年龄
      this.age = age;
  }
  public int getAge(){  //获取年龄
      return age;
  }
  public abstract void eat(); // 吃饭      由于不同的动物的吃饭方法不同，所以这里定义吃饭这个方法为abstract方法，因此，Animal类亦应该定义为abstract类
  }
  
  
      class Cat extends Animal{
      public Cat(){}
  
      public Cat(String name,int age){
      super(name,age);
  }
  
  public void eat(){                                  //猫的吃饭法方法
      System.out.println("猫吃鱼");
  }
  public void catchMousr(){                    //猫的抓老鼠方法
      System.out.println("抓老鼠");
  }
  
  
  class Dog extends Animal{             
  public Dog(){}
  public Dog(String name,int age){
          super(name,age);
  }
  
  public void eat(){                                         //狗的吃饭法方法
      System.out.println("狗吃肉");
      }
  public void lookHome(){                              //狗的看家方法
  System.out.println("看家");
      }
      }