2016/5/18学习记录

1.package

　当在同一个包里面的对象相互调用其他类里面的函数，可以直接使用。

　 Scanner是系统类库里面的，在java.util的包里。

　 String在Java.lang的包里。

　 package是组织代码的一种形式，类的外面package。

　如果不在自己的package里使用其他包里面的函数，用import来实现。

　 Clock.Display.java

　 CLock包里面的Clock.Display包里面的java.

　最终包的关系转化成为文件里面的目录关系　

2.一个继承的小例子

 1 package Pra;
 2 
 3 public class A {
 4     protected  void print(String s ){
 5         System.out.println(s);
 6     } 
 7     A(){
 8         print("AHello");
 9     }
10     public void f(){
11         print("A:GG");
12     }
13     public static void main(String[] args){
14         B b = new B(); b.f();
15         }
16 }
17 class B extends A{
18     B(){print("BHello");}
19     public void f(){print("B:GG");}
20     
21 }

出现了问题一直没有输出，因为之前classA前面没有public,使得main函数没有作用。

3.一个重写的例子

 1 package Pra;
 2 
 3 
 4 class Person {
 5     private String name = "";
 6     private String location = "";
 7     
 8     Person(String name)
 9     {
10         this.name = name ; 
11         this.location = "Beijing";
12     }
13     Person(String name,String location)
14     {
15         this.name = name;
16         this.location = location;
17     }
18     public String info(){
19         return "name: "+name+ "location: "+location;
20     }
21 }    
22 class Student extends Person{
23     private String school = "";
24     Student(String name,String school){
25         this(name,"Beijing",school);}
26     Student(String n,String l,String s){
27         super(n,l);
28         this.school=s;}
29     public String info(){
30         return super.info() + "School: "+school;
31      }
32 }
33 
34 class Teacher extends Person{
35     private String status = "";
36     Teacher(String name,String status) {
37         this(name,"shanghai",status);}
38     Teacher(String n,String l,String s){
39         super(n,l);
40         this.status=s;
41     }    
42     public String info(){
43         return super.info()+"status: "+status;
44     }
45     
46         
47         // TODO Auto-generated constructor stub
48     }
49 
50 public class Text{
51     public static void main(String[] args) {
52         // TODO Auto-generated method stub
53     Person a = new Person("fan","Shanghai"); System.out.println(a.info());
54     Person b = new Person("qf");b.info(); System.out.println(b.info());
55     Student c = new Student("fs", "tongji");  System.out.println(c.info());
56     Student d = new Student("a","shnaghai","asdbf");  System.out.println(d.info());
57     Teacher f = new Teacher("xie","but");System.out.println(f.info());
58     }
59 }

重写