List、Set、Map、数组互转

1.list转set

Set set = new HashSet(new ArrayList());

2.set转list

List list = new ArrayList(new HashSet());

3.数组转为list

List stooges = Arrays.asList("Larry", "Moe", "Curly");  

4.数组转为set (数组先转为list，再从list转为set)

Set set = new HashSet(Arrays.asList(new String[]{"1","2","3"}));

5.list转数组

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

6.map的相关操作

Map map = new HashMap();      
map.put("1", "a");      
map.put('2', 'b');      
map.put('3', 'c');      
System.out.println(map);      
// 输出所有的值      
System.out.println(map.keySet());      
// 输出所有的键      
System.out.println(map.values());      
// 将map的值转化为List      
List list = new ArrayList(map.values());      
System.out.println(list);      
// 将map的值转化为Set      
Set set = new HashSet(map.values());      
System.out.println(set);