ooday02笔记

1. 继承：

   - 作用：代码复用

   - 通过extends实现继承

   - 超类/基类/父类：共有的属性和行为

     派生类/子类：特有的属性和行为

   - 派生类可以访问：超类的+派生类的，超类不能访问派生类的

   - 一个超类可以有多个派生类，一个派生类只能有一个超类---------单一继承

   - 具有传递性

   - java规定：构造派生类之前必须先构造超类

     - 在派生类的构造方法中若没有调用超类的构造方法，则默认super()调用超类的无参构造方法

     - 在派生类的构造方法中若自己调用了超类的构造方法，则不再默认提供

       > 注意：super()调用超类构造方法，必须位于派生类构造方法中的第1行

       ```java
       public class Person {
           String name;
           int age;
           String address;
           Person(String name,int age,String address){
               this.name = name;
               this.age = age;
               this.address = address;
           }
       
           void eat(){
               System.out.println(name+"正在吃饭...");
           }
           void sleep(){
               System.out.println(name+"正在睡觉...");
           }
           void sayHi(){
               System.out.println("大家好，我叫"+name+"，今年"+age+"岁了，家住"+address);
           }
       }
       
       public class Student extends Person{
           String className;
           String stuId;
           Student(String name,int age,String address,String className,String stuId){
               super(name,age,address); //传递的是name/age/address的值
               this.className = className;
               this.stuId = stuId;
           }
       
           void study(){
               System.out.println(name+"正在学习...");
           }
       }
       
       public class Teacher extends Person{
           double salary;
           Teacher(String name,int age,String address,double salary){
               super(name,age,address);
               this.salary = salary;
           }
       
           void teach(){
               System.out.println(name+"正在讲课...");
           }
       }
       
       public class Doctor extends Person {
           String title;
           Doctor(String name,int age,String address,String title){
               super(name,age,address);
               this.title = title;
           }
           void cut(){
               System.out.println(name+"正在做手术...");
           }
       }
       
       public class ExtendsTest {
           public static void main(String[] args) {
               Student zs = new Student("张三",25,"廊坊","jsd2302","001");
               zs.eat();
               zs.sleep();
               zs.sayHi();
               zs.study();
       
               Teacher ls = new Teacher("李四",35,"佳木斯",6000.0);
               ls.eat();
               ls.sleep();
               ls.sayHi();
               ls.teach();
       
               Doctor ww = new Doctor("王五",46,"山东","主任医师");
               ww.eat();
               ww.sleep();
               ww.sayHi();
               ww.cut();
           }
       }
       ```

2. super：指代当前对象的超类对象

   - super.成员变量名-------------------------访问超类的成员变量

     > 当超类成员变量和派生类成员变量同名时，super指超类的，this指派生类的
     >
     > 若没有同名现象，则写super和this是一样的

   - super.方法名()------------------------------调用超类的方法

   - super()----------------------------------------调用超类的构造方法

     ```java
     public class SuperDemo {
         public static void main(String[] args) {
             Boo o = new Boo();
         }
     }
     
     
     //在派生类的构造方法中若自己调用了超类的构造方法，则不再默认提供
     class Coo{
         Coo(int a){
         }
     }
     class Doo extends Coo{
         Doo(){
             super(5);
         }
         /*
         //如下代码为默认的
         Doo(){
             super();
         }
          */
     }
     
     class Aoo{
         Aoo(){
             System.out.println("超类构造方法");
         }
     }
     class Boo extends Aoo{
         Boo(){
             super(); //默认的，调用超类的无参构造方法
             System.out.println("派生类构造方法");
         }
     }
     ```

3. 方法的重写(override/overriding)：重新写、覆盖

   - 发生在父子类中，方法名相同，参数列表相同

   - 重写方法被调用时，看对象的类型---------------new谁就调谁的，这是规定

     ```java
     class 餐馆{
         void 做餐(){ 做中餐 }
     }
     //1)我还是想做中餐----------------------不需要重写
     class Aoo extends 餐馆{
     }
     //2)我想改做西餐------------------------需要重写
     class Boo extends 餐馆{
         void 做餐(){ 做西餐 }
     }
     //3)我想在中餐基础之上加入西餐------------需要重写(先super中餐，再加入西餐)
     class Coo extends 餐馆{
         void 做餐(){
             super.做餐();
             做西餐
         }
     }
     ```

     ```java
     public class Person {
         String name;
         int age;
         String address;
         Person(String name,int age,String address){
             this.name = name;
             this.age = age;
             this.address = address;
         }
     
         void eat(){
             System.out.println(name+"正在吃饭...");
         }
         void sleep(){
             System.out.println(name+"正在睡觉...");
         }
         void sayHi(){
             System.out.println("大家好，我叫"+name+"，今年"+age+"岁了，家住"+address);
         }
     }
     
     public class Student extends Person{
         String className;
         String stuId;
         Student(String name,int age,String address,String className,String stuId){
             super(name,age,address); //传递的是name/age/address的值
             this.className = className;
             this.stuId = stuId;
         }
     
         void study(){
             System.out.println(name+"正在学习...");
         }
         
         void sayHi(){
             System.out.println("大家好，我叫"+name+"，今年"+age+"岁了，家住"+address+"，所在班级为:"+className+"，学号为："+stuId);
         }
     }
     
     public class Teacher extends Person{
         double salary;
         Teacher(String name,int age,String address,double salary){
             super(name,age,address);
             this.salary = salary;
         }
     
         void teach(){
             System.out.println(name+"正在讲课...");
         }
         
         void sayHi(){
             System.out.println("大家好，我叫"+name+"，今年"+age+"岁了，家住"+address+"，工资为:"+salary);
         }
     }
     
     public class Doctor extends Person {
         String title;
         Doctor(String name,int age,String address,String title){
             super(name,age,address);
             this.title = title;
         }
         void cut(){
             System.out.println(name+"正在做手术...");
         }
     }
     
     public class ExtendsTest {
         public static void main(String[] args) {
             Student zs = new Student("张三",25,"廊坊","jsd2302","001");
             zs.eat();
             zs.sleep();
             zs.sayHi();
             zs.study();
     
             Teacher ls = new Teacher("李四",35,"佳木斯",6000.0);
             ls.eat();
             ls.sleep();
             ls.sayHi();
             ls.teach();
     
             Doctor ww = new Doctor("王五",46,"山东","主任医师");
             ww.eat();
             ww.sleep();
             ww.sayHi();
             ww.cut();
         }
     }
     ```

4. 综合练习：

   ```java
   public class Animal {
       String name;
       int age;
       String color;
       Animal(String name,int age,String color){
           this.name = name;
           this.age = age;
           this.color = color;
       }
       void drink(){
           System.out.println(color+"色的"+age+"岁的"+name+"正在喝水...");
       }
       void eat(){ //---------------明天继续改造
           System.out.println(color+"色的"+age+"岁的"+name+"正在吃饭...");
       }
   }
   
   public class Dog extends Animal {
       Dog(String name,int age,String color){
           super(name,age,color);
       }
       void lookHome(){
           System.out.println(color+"色的"+age+"岁的狗狗"+name+"正在看家...");
       }
       void eat(){
           System.out.println(color+"色的"+age+"岁的狗狗"+name+"正在吃肯头...");
       }
   }
   
   public class Chick extends Animal {
       Chick(String name,int age,String color){
           super(name,age,color);
       }
       void layEggs(){
           System.out.println(color+"色的"+age+"岁的小鸡"+name+"正在下蛋...");
       }
       void eat(){
           System.out.println(color+"色的"+age+"岁的小鸡"+name+"正在吃小米...");
       }
   }
   
   public class Fish extends Animal {
       Fish(String name,int age,String color){
           super(name,age,color);
       }
       void eat(){
           System.out.println(color+"色的"+age+"岁的小鱼"+name+"正在吃小虾...");
       }
   }
   
   public class Test {
       public static void main(String[] args) {
           Dog dog1 = new Dog("小黑",2,"黑");
           dog1.eat();
           dog1.drink();
           dog1.lookHome();
   
           Dog dog2 = new Dog("小白",1,"白");
           dog2.eat();
           dog2.drink();
           dog2.lookHome();
   
           Dog dog3 = new Dog("小强",2,"黑白");
           dog3.eat();
           dog3.drink();
           dog3.lookHome();
   
           Chick chick = new Chick("花花",1,"棕");
           chick.eat();
           chick.drink();
           chick.layEggs();
   
           Fish fish = new Fish("金金",2,"金");
           fish.eat();
           fish.drink();
       }
   }
   ```
   
   

## 补充：

1. 泛化：从程序设计角度而言叫泛化，从代码实现角度而言叫继承，泛化就是继承

2. 继承要符合is(是)的关系

3. 继承的是超类的成员变量和普通方法，不包括超类的构造方法，超类的构造方法是被派生类通过super()来调用的，而不是继承的

   ```java
   class Aoo{
       int a;
       Aoo(){
       }
       void show(){
       }
   }
   class Boo extends Aoo{
       继承了Aoo类的a+show()，并没有继承Aoo类的构造方法
   }