1.list轉set
Set set = new HashSet(new ArrayList()); 

2.set轉list
List list = new ArrayList(new HashSet());

3.數組轉為list
List stooges = Arrays.asList("Larry", "Moe", "Curly");
或者
String[] arr = {"1", "2"};
List list = Arrays.asList(arr);

4.數組轉為set
int[] a = { 1, 2, 3 };
Set set = new HashSet(Arrays.asList(a));

5.map的相關操作。
Map map = new HashMap();
map.put("1", "a");
map.put('2', 'b');
map.put('3', 'c');
System.out.println(map);
// 輸出所有的值
System.out.println(map.keySet());
// 輸出所有的鍵
System.out.println(map.values());
// 將map的值轉化為List
List list = new ArrayList(map.values());
System.out.println(list);
// 將map的值轉化為Set
Set set = new HashSet(map.values());
System.out.println(set);

6.list轉數組
List list = Arrays.asList("a","b");
String[] arr = (String[])list.toArray(new String[list.size()]);
System.out.println(Arrays.toString(arr));