java String List Array Map Set 字符串和集合互转

数组 Array 转 List

String[] ss = { "JJ", "KK" };
List<String> list1 = Arrays.asList(ss);
List<String> list2 = Arrays.asList("AAA", "BBB");
System.out.println(list1);
System.out.println(list2);

List 转数组 Array

List<String> list = new ArrayList<>();
list.add("AA");
list.add("BB");
list.add("CC");
//List --> Array
String[] arr = new String[list.size()];
list.toArray(arr);
System.out.println("arr:" + Arrays.toString(arr));
String[] str = list.toArray(new String[] {});
System.out.println("str:" + Arrays.toString(str));

Set 转 List

Set<String> set = new HashSet<>();
set.add("AA");
set.add("BB");
set.add("CC");
//Set --> List
List<String> setList = new ArrayList<>(set);
System.out.println(setList);

List 转 Set

List<String> list = new ArrayList<>();
list.add("ABC");
list.add("EFG");
list.add("LMN");
//List-->Set
Set<String> listSet = new HashSet<>(list);
System.out.println(listSet);

Set 转 数组 Array

Set<String> set = new HashSet<>();
set.add("AA");
set.add("BB");
set.add("CC");

String[] arr = new String[set.size()];
//Set-->数组
set.toArray(arr);
System.out.println(Arrays.toString(arr));

数组 Array 转 Set

String[] arr = {"AA", "BB", "DD", "CC", "BB"};
//数组-->Set
Set<String> set = new HashSet<>(Arrays.asList(arr));
System.out.println(set);

Map 转 List

Map<String, String> map = new HashMap<>();
map.put("A", "ABC");
map.put("K", "KK");
map.put("L", "LV");

// 将Map Key 转化为List
List<String> mapKeyList = new ArrayList<>(map.keySet());
System.out.println("mapKeyList:" + mapKeyList);

// 将Map value 转化为List
List<String> mapValuesList = new ArrayList<>(map.values());
System.out.println("mapValuesList:" + mapValuesList);

Map 转 Set

Map<String, String> map = new HashMap<>();
map.put("A", "ABC");
map.put("K", "KK");
map.put("L", "LV");

// 将Map 的键转化为Set
Set<String> mapKeySet = map.keySet();
System.out.println("mapKeySet:" + mapKeySet);

// 将Map 的值转化为Set
Set<String> mapValuesSet = new HashSet<>(map.values());
System.out.println("mapValuesSet:" + mapValuesSet);

数组 Array 转 String

Array转String
//方法1：
//需要引入Apache common包中的个commons-lang.jar包：
String[] ary = { "1", "2" };
String str = StringUtils.join(ary, ",");
System.out.println(str);

List 转 String

List<String> list = new ArrayList<>();
list.add("a");
list.add("b");
list.add("c");

 StringJoiner result = new StringJoiner(",");
 for (String s : list) {
     result.add(s);
 }
 System.out.println(result.toString());

String 转数组 Array

String str = "1,2,3,4,"; //最后的逗号不用截取 print {"1","2","3","4"}
String[] array = str.split(",");
System.out.println(Arrays.toString(array));