import java.util.Arrays;

import java.util.HashMap;

import java.util.Map;

import java.util.Set;

/**

* @ClassName GenericDemo

* @Description GenericDemo use Wildcard，用在寫框架或是API較靈活通用，理解用法後對於讀源碼會有所幫助

* @Author kyocoolcool

* @Date 2019-08-13 00:06

* @Version 1.0

**/

public class GenericDemo {

public static void main(String[] args) {

Bag<Integer> bag = new Bag<>();

bag.data=20;

bag.getBag(1);

Bag<String> bag2 = new Bag<>();

bag2.getBag("hello");

bag2.data="apple";

Bag<Number> bag3 = new Bag<>();

bag3.data = 100;

bag3.getBag(10);

Bag<? extends Number> bag4 = new Bag<>();

/* 通用符 ? extends */

getUp(bag);

// getUp(bag2);//僅支援Number及其子類

getUp(bag3);

System.out.println("-------------");

/* 通用符 ? super */

getUp2(bag);

getUp2(bag3);

/* 泛型方法調用*/

String[] arrays={"AAA","BBBB","CCC","DDD"};

String[] fun = GenericDemo.fun(arrays, 1, 3);

System.out.println("--------------");

System.out.println(Arrays.toString(fun));

System.out.println("--------------");

/* Set裡的范型E，裡面放著Map，Map裡面放著Integer,String */

HashMap<Integer, String> map = new HashMap<>();

map.put(1, "apple");

map.put(2, "lemon");

Set<Map.Entry<Integer, String>> set = map.entrySet();

for (Map.Entry entry : set) {

System.out.println(entry.getKey()+"----"+entry.getValue());

}

}

/* ? extends 用法 */

public static void getUp(Bag<? extends Number> bag) {

System.out.println("data:"+bag.getBag());

}

/* ? super 用法 */

public static void getUp2(Bag<? super Integer> bag) {

System.out.println("data:"+bag.getBag());

}

/* 范型方法 */

public static <T> T[] fun(T[] array,int x,int y) {

T temp = array[x];

array[x] = array[y];

array[y] = temp;

return array;

}

}