java中List、Array、Map、Set等集合相互转

 

1.List转换为Array

List<String> list = new ArrayList<>();

list.add("AAAA");

list.add("BBBB");

list.add("CCCC");

list.add("DDDD");

String [] array = list.toArray(new String[list.size()]);

2.

Array转换为List

String[] countries = {"AAAA", "BBBB", "CCCC", "DDDD"};

List list = Arrays.asList(countries);

3.

Map的Key值转换为List

Map<Integer,String> map = new HashMap<>();

map.put(1,"AAAA");

map.put(2,"BBBB");

map.put(3,"CCCC");

map.put(4,"DDDD");

List<Integer> list = new ArrayList<Integer>(map.keySet());

4.

Map的Value值转换为List

Map<Integer,String> map = new HashMap<>();

map.put(1,"AAAA");

map.put(2,"BBBB");

map.put(3,"CCCC");

map.put(4,"DDDD");

List<String> list = new ArrayList<String>(map.values());

5.

Array转换为Set

String [] countries = {"AAAA", "BBBB", "CCCC", "DDDD"};

Set<String> set = new HashSet<String>(Arrays.asList(countries));

注：如果Array中存在相同的值，Set中只会存在一个

6.

Map的Key值转换为Set

Map<Integer,String> map = new HashMap<>();

map.put(1,"AAAA");

map.put(2,"BBBB");

map.put(3,"CCCC");

map.put(4,"DDDD");

Set<Integer> set = new HashSet<>(map.keySet());

7.

Map的Value值转换为Set

Map<Integer,String> map = new HashMap<>();

map.put(1,"AAAA");

map.put(2,"BBBB");

map.put(3,"CCCC");

map.put(4,"DDDD");

Set<String> set = new HashSet<String>(map.values());