用继承集中管理代码

Java 面向对象编程入门

Sani Yusuf

Lead Software Engineering Content Developer

处理多个类

  // Toyota class
  class Toyota {
      public String model;
      public String color;
      public String licensePlate;  
  }

  // Honda class
  class Honda {
      public String model;
      public String color;
      public String licensePlate;       
  }

  // Mercedes class
  class Mercedes {
      public String model;
      public String color;
      public String licensePlate;        
  }

处理类时常见代码重复

继承的威力

继承可消除重复代码
可将共享代码集中在一处
其他类用 extends 继承

  // Car class
  class Car {
     // All public properties 
     // are inherited
     public String model;
     public String color;
     public String licensePlate;  
 }

  // Toyota inheriting from Car class
  class Toyota extends Car {

  }

  // Honda inheriting from Car class
  class Honda extends Car {

  }

  // Mercedes inheriting from Car class
  class Mercedes extends Car {

  }

基类简介

基类包含共享代码
Car 类是基类示例


  class Car {
     public String model;
     public String color;
     public String licensePlate;  
 }

通过子类继承

子类是继承基类的类
Toyota 类是子类示例
子类继承基类的所有 public 属性和方法
super() 调用基类构造函数

  // Car Base Class
  class Car {
     public String model;
     public String color;
     public String licensePlate;  
 }

 // Toyota subclass
  class Toyota extends Car {


     // Toyota constructor
     public Toyota(){ 
       // super() calls 
       // baseclass constructor (Car)
       super();
     }
  }

创建继承实例

实例对象可使用来自基类的属性


  // Car class  
  class Car {
    public String color;   

    // Car constructor
    public Car(String color){
      this.color = color;
    }    
  }


  // Toyota subclass
  class Toyota extends Car {
     public Toyota(){
       super();
     }
  }

  // Main class 
  public class Main {
    public static void main(String[] args) {
        Toyota myToyota = new Toyota("Brown");
        // "color" property inherited from "Car"
        System.out.println(
          myToyota.color); // Brown
    }
  }

Passons à la pratique !

Java 面向对象编程入门