List、Array、Set相互转换

1、list 转换为Array

List<String> list = new ArrayList<>();
     list.add("AAAA");
     list.add("BBBB");
     list.add("CCCC");
     list.add("DDDD");
     System.out.println(list);//输出 [AAAA, BBBB, CCCC, DDDD]

     String [] array = list.toArray(new String[list.size()]);

2、Array转换为List

String[] countries = {
    
    "AAAA", "BBBB", "CCCC", "DDDD"};
    List list = Arrays.asList(countries);
    
    System.out.println(list);//输出[AAAA, BBBB, CCCC, DDDD]

3、Array转换为Set

String [] countries = {
    
    “AAAA”, “BBBB”, “CCCC”, “DDDD”};
Set<String> set = new HashSet<String>(Arrays.asList(countries));

System.out.println(set);//输出[AAAA, BBBB, CCCC, DDDD]
注：如果Array中存在相同的值，Set中只会存在一个