list,set,map,数组间的相互转换

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");
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));
5.map的相关操作。

1.Map map = new HashMap();
2.map.put( "1" , "a" );
3.map.put( '2' , 'b' );
4.map.put( '3' , 'c' );
5.System.out.println(map);
6. // 输出所有的键
7.System.out.println(map.keySet());
8. // 输出所有的值
9.System.out.println(map.values());
10.// 将map的值转化为List
11.List list = new ArrayList(map.values());
12.System.out.println(list);
13.// 将map的值转化为Set
14.Set set = new HashSet(map.values());
15.System.out.println(set);
6.list转数组

1.List list = Arrays.asList( "a" , "b" );
2.System.out.println(list);
3.
4.String[] arr = (String[])list.toArray( new String[list.size()]);
5.System.out.println(Arrays.toString(arr));