Java 集合转换(数组、List、Set、Map相互转换)

public static void main(String[] args) {

  testList2Array();
  testArray2List();
  testSet2List();
  testList2Set();
  testSet2Array();
  testArray2Set();
  testMap2Set();
  testMap2List();
}

private static void testMap2List() {

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

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

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

}

private static void testMap2Set() {

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

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

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

private static void testArray2Set() {

  String[] arr = { "AA", "BB", "DD", "CC", "BB" };

  // 数组-->Set
  Set set = new HashSet(Arrays.asList(arr));
  System.out.println(set);
}

private static void testSet2Array() {
  Set 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));
}

private static void testList2Set() {

  List list = new ArrayList();
  list.add("ABC");
  list.add("EFG");
  list.add("LMN");
  list.add("LMN");

  // List-->Set
  Set listSet = new HashSet(list);
  System.out.println(listSet);
}

private static void testSet2List() {

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

  // Set --> List
  List setList = new ArrayList(set);
  System.out.println(setList);
}

private static void testList2Array() {
  // List-->数组
  List list = new ArrayList();
  list.add("AA");
  list.add("BB");
  list.add("CC");
  Object[] objects = list.toArray();// 返回Object数组
  System.out.println("objects:" + Arrays.toString(objects));

  String[] arr = new String[list.size()];
  list.toArray(arr);// 将转化后的数组放入已经创建好的对象中
  System.out.println("strings1:" + Arrays.toString(arr));
}

private static void testArray2List() {
  // 数组-->List
  String[] ss = { "JJ", "KK" };
  List list1 = Arrays.asList(ss);
  List list2 = Arrays.asList("AAA", "BBB");
  System.out.println(list1);
  System.out.println(list2);
}