疯狂java学习笔记之面向对象(七) - super关键字

 1 class Fruit{
 2     private String color;
 3     private double weight;
 4     
 5     public Fruit(){}
 6     public Fruit(String color , double weight){
 7         this.color = color;
 8         this.weight = weight;
 9     }
10 
11     public void info(){
12         System.out.println("这是一个水果哦!");
13         System.out.println("水果颜色是:" + color + ",重量为:" + weight);
14     }
15 }
16 
17 
18 public class Apple extends Fruit{
19     public void info(){
20         System.out.println("这是个苹果!");
21     }
22 
23     public void test(){
24         System.out.println("~~Apple test 方法");
25         //this.info(); - 通过this. 调用info默认总是调用本类中定义的info()方法
26         super.info();  //- 通过super. 限定后强制调用父类中的info()方法
27     }
28 
29     public static void main(String[] args){
30         Apple a = new Apple();
31         a.test();
32     }
33 }

 1 class Demo{
 2     int count = 2;
 3 }
 4 
 5 public class TestDemo extends Demo{
 6     int count = 10;
 7     public void test(){
 8         //默认count(即count前不加this./super.)时,其前面默认省略了this
 9         //若一定要使用父类的count Field必须在其前面加上super.
10         System.out.println("test方法访问当前类的count为:" + this.count);
11         System.out.println("test方法访问父类的count为:" + super.count);
12     }
13 
14     public static void main(String[] args){
15         TestDemo t = new TestDemo();
16         t.test();
17     }
18 }

 1 class Person{
 2     protected String name;
 3     protected int age;
 4     protected String sex;
 5 
 6     //程序员定义了有参构造器,因此系统不会再为该类生成无参构造器
 7     public Person(String name , int age , String sex){
 8         this.name = name;
 9         this.age = age;
10         this.sex = sex;
11     }
12 
13     //假如不定义方法,直接在main方法中调用name/age/sex 参数编译时会报错"staic方法不能引用非static变量"
14     public void info(){
15         System.out.println("老师的名字叫:" + name + ",年龄为:" + age + ",性别为:" + sex);
16     }
17 }
18 
19 public class Teacher extends Person{
20     private String sex;
21 
22     //若不指定构造器,默认会去调用父类的无参构造器,但父类又没有无参构造器则报错
23     public Teacher(String name , int age , String sex){
24         super(name,age,sex);
25     }
26     
27     
28     public static void main(String[] args){
29         Teacher tt = new Teacher("haha",30,"male");
30         tt.info();
31     }
32 }