array
ArrayList
1 //声明25个元素的数组
2 int[] num = new int[25];
3 //初始化 长度3的字符窜数组
4 String[] str = {"a", "b", "c"};
5 //遍历
6 for (int i = 0; i < 25; i++) {
7 num[i] = i * 3;
8
9 }
10 for (int n : num) {
11 System.out.println(n);
12 }
13 //遍历
14 for (String s : str) {
15 System.out.printf("%s", s);
16 }
17
18ArrayList<String> list = new ArrayList<>();
19 list.add("abc");
20 list.add("dddd");
21
22 //for循环遍历
23 for (String s : list) {
24 System.out.println(s + "");
25 }
26
27 //迭代器遍历
28
29 Iterator<String> iterator = list.iterator();
30 while (iterator.hasNext()) {
31 System.out.println("迭代器遍历 " + iterator.next());
32 }
33
34 //索引遍历
35
36 for (int i = 0; i < list.size(); i++) {
37 System.out.println("索引遍历 key " + i + " value " + list.get(i));
38
39 }
40
41 //ArrayList 转为数组
42 String[] strings = list.toArray((new String[0])); //常用
43 String[] strings1 = new String[list.size()];//容易理解
44
45 //移除某个元素
46 list.remove(1);
47 list.clear();//清空数组
48
49 System.out.println(list);
50
1
2//创建map
3 HashMap<String, String> map = new HashMap<>();
4 map.put("test1", "wacx");
5 map.put("test2", "wwww");
6
7 //1 遍历
8 for (Map.Entry<String, String> entry : map.entrySet()) {
9
10 System.out.println("key = " + entry.getKey() + " value = " + entry.getValue());
11 }
12
13
14 // 2 分别遍历key value
15 for ( String key :map.keySet()) {
16 System.out.printf("key %s \n" ,key);
17 }
18
19 for (String value : map.values()) {
20 System.out.printf("值 %s \n",value);
21 }
22
23 //使用迭代器
24 Iterator<Map.Entry<String, String>> iterator = map.entrySet().iterator();
25
26 while (iterator.hasNext()) {
27 Map.Entry<String, String> next = iterator.next();
28 System.out.printf("key %s value %s \n",next.getKey(),next.getValue());
29 }
30
31
32