继承

继承   是通过关键字 extends来实现的

语法：子类  extends 父类{

            //类定义部分

          }

下面来看一个例子：

 

package jicheng;

public class Pet {
   private int health;
   private String name;
   public Pet(){
       health=95;
   }
   public Pet(String name){
       this.name=name;
   }
public int getHealth() {
    return health;
}
public void setHealth(int health) {
    this.health = health;
}
public String getName() {
    return name;
}
public void setName(String name) {
    this.name = name;
}
/**
 * 输出宠物信息
 */
public void print(){
    System.out.println("宠物的自白：\n我的名字叫"+this.name+"我的健康值："+this.health);
}

   
   
}

 

package jicheng;

public class Doog extends Pet{
      private String strain;
      public Doog(String name, String strain){
          super(name);
          this.strain=strain;
      }
      public String getStrain(){
          return strain;
      }
}

package jicheng;

public class Penguin extends Pet{
    private String sex;
    public Penguin (String name,String sex){
        super(name);
        this.sex=sex;
        }
       public String getSex(){
           return sex;
    }
}

package jicheng;

public class MyPestText {
    public static void main(String[] args) {
        Pet pet=new Pet("贝贝");
        pet.print();
        Doog dog=new Doog("狗狗","藏獒");
        dog.print();
        Penguin pen=new Penguin("bala","雄");
        pen.print();
    }
}

子类重写父类的方法

package boke;

public class Pet {
       private int health;
       private String name;
       public Pet(){
           health=95;
           name="ss";
       }
       public Pet(String name){
           this.name=name;
       }
    public int getHealth() {
        return health;
    }
    public void setHealth(int health) {
        this.health = health;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    /**
     * 输出宠物信息
     */
    public void print(){
        System.out.println("宠物的自白：\n我的名字叫"+this.name+"我的健康值："+this.health);
    }

       
       
    }

package boke;

public class Dog extends Pet {
    /**
     * 狗狗类Pet的子类
     */
    public  String strain;
    /**
     * 有参构造方法
     */
    public Dog(String name ,String strain){
        //super(name);
        this.strain=strain;
    }
    public String getStrain(){
        return strain;
    }
    /**
     * 重写父类的方法
     */
    public void print(){
        super.print();
        System.out.println("我是一个"+this.strain);
    }
}

package boke;

public class Penguin extends Pet {
   private String sex;//性别
   public Penguin(String name,String sex){
       super(name);
       this.sex=sex;
   }
   public String getSex(){
       return sex;
   }
   /**
    * 重写父类的print方法
    */
   public void print(){
       super.print();
       System.out.println("性别是："+this.sex);
   }
}

package boke;

public class Test {
    public static void main(String[] args) {
        Pet pet=new Pet("贝贝");
        pet.print();
        Dog dog=new Dog("狗狗","藏獒");
        dog.print();
        Penguin pen=new Penguin("bala","雄");
        pen.print();
    }
}

继承关系中的构造方法

package boke;
public class Person {
      String name;
      public Person(){
          System.out.println("execue Person()");
      }
      public Person(String name){
          this.name=name;
          System.out.println("execue Person(name)");
      }
}

package boke;

public class Student extends Person{
      public String school;
     public Student(){
         System.out.println("execue Person(name)");
     }
     public Student(String name,String school){
         super(name);
         this.school=school;
     }
}

package boke;

public class PostGraduate  extends Student {
     String guide;
     public PostGraduate(){
         System.out.println("execue PostGraduate ");
     }
     public PostGraduate (String name,String school,String guide){
         super(name,school);
         this.guide=guide;
         System.out.println("execue  PostGraduate( name,School, guide) ");
     }
     
}

package boke;

public class Testi {
    public static void main(String[] args) {
        PostGraduate pg=null;
        pg=new PostGraduate();
        System.out.println();
        pg=new PostGraduate( "留","下","来");
    }
}