集合与数组的转换

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

 

int[] a = { 1, 2, 3 };
List list = Arrays.asList(a);

int[] a = { 1, 2, 3 };
List list = Arrays.asList(a);

 注意：此时list的长度为1

4.数组转为set

 

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

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

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));