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

package Pra;

public class A {
    protected  void print(String s ){
        System.out.println(s);
    } 
    A(){
        print("AHello");
    }
    public void f(){
        print("A:GG");
    }
    public static void main(String[] args){
        B b = new B(); b.f();
        }
}
class B extends A{
    B(){print("BHello");}
    public void f(){print("B:GG");}
    
}    

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

package Pra;


class Person {
    private String name = "";
    private String location = "";
    
    Person(String name)
    {
        this.name = name ; 
        this.location = "Beijing";
    }
    Person(String name,String location)
    {
        this.name = name;
        this.location = location;
    }
    public String info(){
        return "name: "+name+ "location: "+location;
    }
}    
class Student extends Person{
    private String school = "";
    Student(String name,String school){
        this(name,"Beijing",school);}
    Student(String n,String l,String s){
        super(n,l);
        this.school=s;}
    public String info(){
        return super.info() + "School: "+school;
     }
}

class Teacher extends Person{
    private String status = "";
    Teacher(String name,String status) {
        this(name,"shanghai",status);}
    Teacher(String n,String l,String s){
        super(n,l);
        this.status=s;
    }    
    public String info(){
        return super.info()+"status: "+status;
    }
    
        
        // TODO Auto-generated constructor stub
    }

public class Text{
    public static void main(String[] args) {
        // TODO Auto-generated method stub
    Person a = new Person("fan","Shanghai"); System.out.println(a.info());
    Person b = new Person("qf");b.info(); System.out.println(b.info());
    Student c = new Student("fs", "tongji");  System.out.println(c.info());
    Student d = new Student("a","shnaghai","asdbf");  System.out.println(d.info());
    Teacher f = new Teacher("xie","but");System.out.println(f.info());
    }
}