Java 基础

笔记:

/**1.定义一个PairTest泛型类, 测试泛型 类 Pair的用法
 * class Pair<T>{
 *     private T first;
 *     private T second;
 *     ............(方法get/set 全部自动生成)
 *     }
 * 2.泛型方法的使用; 创建一个泛型方法: 格式: [public...访问修订符] [static][final]  <T> void classname(T x){ ... }
 * 3.类型通配符为'?',仅可以用来声明变量!不可以声明类!  void showClassName(Status<?>ob)  ;默认上界是 Number
 */

测试代码:

public class Test泛型 {
    public static void main(String[] args){
            //1.定义一个PairTest类, 测试泛型类Pair的用法
        Pair<String> pair=new Pair<String>("Hello","Java");
        System.out.print("first = "+pair.getFirst());
        System.out.println(", second = "+pair.getSecond());
        System.out.println("-----------------------------");
            //2.泛型方法的使用; 创建一个泛型方法;
        GenericMethod gm = new GenericMethod();
        gm.showClassName("c");
        gm.showClassName(1);
        gm.showClassName('a');
        gm.showClassName(gm);
            //3.通配类型参数;
        Integer inums[]={1,2,3,4,5};
        Status<Integer> iobj=new Status<>(inums);

        Double dnums[]={1.1,2.2,3.3,4.4,5.5};
        Status<Double> dobj=new Status<>(dnums);
        iobj.showClassName(iobj);
        iobj.showClassName(dobj);  //将void showClassName(Status<T>ob) 改为:void showClassName(Status<?>ob)
    }
}
class Pair<T>{
    private T first;
    private T second;
    public Pair() {
        this.first = null;
        this.second = null;
    }
    public Pair(T first, T second) {
        this.first = first;
        this.second = second;
    }

    public T getFirst() {
        return first;
    }
    public void setFirst(T first) {
        this.first = first;
    }
    public T getSecond() {
        return second;
    }
    public void setSecond(T second) {
        this.second = second;
    }
}
class GenericMethod{
    public <T> void showClassName(T x){
        System.out.println(x+"'s classname: "+x.getClass().getName());
    }
}
class Status<T extends Number>{
    T[] nums;
    public Status(T[] nums) {
        this.nums = nums;
    }
    void showClassName(Status<?>ob){
        System.out.println("[3] classname: "+ob.getClass().getName());
    }
}

测试结果:

first = Hello, second = Java
-----------------------------
c's classname: java.lang.String
1's classname: java.lang.Integer
a's classname: java.lang.Character
任务168.GenericMethod@3567135c's classname: 任务168.GenericMethod
[3] classname: 任务168.Status
[3] classname: 任务168.Status