泛型的上下限定义

class Info<T>{
    private T var;
    public T getVar(){
        return var;
    }
    public void setVar(T var){
        this.var=var;
    }
    public String toString(){
        return this.var.toString();
    }
}
public class GenericsDemo17 {
public static void main(String[] args) {
    Info<Integer> i1=new Info<Integer>();
    Info<Float> i2=new Info<Float>();
    Info<String> i3=new Info<String>();
    i1.setVar(30);
    i2.setVar(30.1f);
    i3.setVar("vonkenmo");
    fun1(i1);
    fun1(i2);
//    fun1(i3);
    fun2(i3);   
}
public static void fun1(Info<? extends Number> i3){
    System.out.println(i3+",");
}
public static void fun2(Info<? super String> i3){
    System.out.println(i3+",");
}
}