Java集合复习Collection添加一组元素

Posted 2020-10-12 vector11248

 1 import java.util.*;
 2 class Snow{}
 3 class Powder extends Snow{}
 4 class Crusty extends Snow{}
 5 class Slush extends Snow{}
 6 
 7 class Light extends Powder {}
 8 class Heavy extends Powder {}
 9 
10 
11 public class AddingGroups {
12 
13     public static void main(String[] args) {
14 
15         Collection<Integer> collection = new ArrayList<Integer>(Arrays.asList(1,2,3));
16         Integer[] moreInts = {4,5,6};
17         //Arrays.asList 顾名思义，传进去一个数组，搞出来一个List。数组转换为List
18         collection.addAll(Arrays.asList(moreInts));
19         Collections.addAll(collection, 7);//可变参数列表
20         
21         /* Arrays.asList()的底层实现是用数组，因此不能调整尺寸。所以运行时会出现UnsupportedOperationException
22         List list = Arrays.asList(1,2,3);
23         list.add(4);
24         System.out.println(list);
25         */
26         System.out.println(collection);
27         
28         List<Snow> snow1 = Arrays.asList(new Powder(),new Slush(),new Crusty());
29         
30         List<Snow> snow2 = Arrays.asList(new Light(),new Heavy());
31         
32 //        Collections.addAll(snow2);
33         
34         List<Snow> snow3 = new ArrayList<Snow>();
35         
36         Collections.addAll(snow3, new Light(),new Heavy());
37         
38         //显式类型参数说明
39         List<Snow> snow4 = Arrays.<Snow>asList(new Light(),new Heavy());
40         
41         
42     }
43 
44 }