list,set,map,数组间的相互转换

  1.list转set 

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

 2.set转list

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

  3.数组转为list

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

此时stooges中有有三个元素。 

 4.数组转为set

int[] a = { 1, 2, 3 };  

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

 5.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);  

 6.list转数组

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));