list,set,map,數組間的相互轉換

         

JavaCC++C# 

1.list轉set

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

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

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

2.set轉list

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

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

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

3.數組轉爲list

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

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

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

此時stooges中有有三個元素。
4.數組轉爲set
int[] a = { 1, 2, 3 };  

Set set = new HashSet(Arrays.asList(a));

Set set = new HashSet(Arrays.asList(a));

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的值轉化爲List
List list = new ArrayList(map.values());
System.out.println(list);
// 將map的值轉化爲Set
Set set = new HashSet(map.values());
System.out.println(set);

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的值轉化爲List
List list = new ArrayList(map.values());
System.out.println(list);
// 將map的值轉化爲Set
Set set = new HashSet(map.values());
System.out.println(set);

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的值轉化爲List   
List list = new ArrayList(map.values());   
System.out.println(list);   
// 將map的值轉化爲Set   
Set set = new HashSet(map.values());   
System.out.println(set);  

6.list轉數組

List list = Arrays.asList("a","b");
System.out.println(list);

String[] arr = (String[])list.toArray(new String[list.size()]);
System.out.println(Arrays.toString(arr));

List list = Arrays.asList("a","b");
System.out.println(list);

String[] arr = (String[])list.toArray(new String[list.size()]);
System.out.println(Arrays.toString(arr));