泛型作用：
泛型：集合类添加对象不用强转
反射机制：将泛型固定的类的所有方法和成员全部显示出来
核心代码：
ArrayList<Ls> ff=new ArrayList()<Ls>;
Ls ls1=new Ls("薯片",5f);
ff.add(ls1);
Ls cls=ff.get(0);//这里不再需要强转
代码实例：
说明：这是非泛型的代码，集合类中调用对象时需要强转
import java.util.*;
public class L4_6
{
public static void main(String[] args)
{
//Hashtable ff=new Hashtable();
ArrayList ff=new ArrayList();
Ls ls1=new Ls("薯片",5f);
ff.add(ls1);
Ls cls=(Ls)ff.get(0);
Yl hyl=(Yl)ff.get(0);//这样显然是不对的
}
}
class Ls
{
private String mingcheng;
private float jiage;
Ls(String mingcheng,float jiage)
{
this.mingcheng=mingcheng;
this.jiage=jiage;
}
}
class Yl
{
private String mingcheng;
private float jiage;
private String yanse;
Yl(String mingcheng,float jiage,String yanse)
{
this.mingcheng=mingcheng;
this.jiage=jiage;
this.yanse=yanse;
}
}