java 继承时候类的执行顺序问题

java 继承时候类的执行顺序问题

子类在继承父类后，创建子类对象会首先调用父类的构造函数，先执行父类的构造函数，然后再执行子类的构造函数，如下所示：

 1 class Father{  
 2     public Father(){  
 3         System.out.println("I am father");  
 4     }  
 5 }  
 6 public class Child extends Father{  
 7     public Child(){   
 8         System.out.println("I am child");  
 9     }  
10     public static void main(String[] args) {  
11         Father f=new Father();  
12         Child c=new Child();  
13     }  
14 }

当父类有带参数的构造函数时，子类默认是调用不带参数的构造函数，如下所示：

 1 class Father{  
 2     public Father(){  
 3         System.out.println("I am father");  
 4     }  
 5     public Father(String name){  
 6         System.out.println("I am father,My name is "+name);  
 7     }  
 8 }  
 9 public class Child extends Father{  
10     public Child(){   
11         System.out.println("I am child");  
12     }  
13     public static void main(String[] args) {  
14         Father f=new Father("Apache");  
15         Child c=new Child();  
16     }  
17 }

若想子类调用父类带参数的构造函数，需要用super()函数申明，如下：

 1 class Father{  
 2     public Father(){  
 3         System.out.println("I am father");  
 4     }  
 5     public Father(String name){  
 6         System.out.println("I am father,My name is "+name);  
 7     }  
 8 }  
 9 public class Child extends Father{  
10     public Child(){   
11         super("Apache");  
12         System.out.println("I am child");  
13     }  
14     public static void main(String[] args) {  
15         Father f=new Father("Apache");  
16         Child c=new Child();  
17     }  
18 }

 

posted @ 2017-09-03 22:09  赵大侠1  阅读(653)  评论(0)  编辑  收藏  举报