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Java 集合轉換(數組、List、Set、Map相互轉換)
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");
// 將Map Key 轉化爲List
List<String> mapKeyList = new ArrayList<String>(map.keySet());
System.out.println("mapKeyList:" + mapKeyList);
// 將Map Key 轉化爲List
List<String> mapValuesList = new ArrayList<String>(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");
// 將Map 的鍵轉化爲Set
Set<String> mapKeySet = map.keySet();
System.out.println("mapKeySet:" + mapKeySet);
// 將Map 的值轉化爲Set
Set<String> mapValuesSet = new HashSet<String>(map.values());
System.out.println("mapValuesSet:" + mapValuesSet);
}
private static void testArray2Set() {
String[] arr = { "AA", "BB", "DD", "CC", "BB" };
// 數組-->Set
Set<String> set = new HashSet<String>(Arrays.asList(arr));
System.out.println(set);
}
private static void testSet2Array() {
Set<String> set = new HashSet<String>();
set.add("AA");
set.add("BB");
set.add("CC");
String[] arr = new String[set.size()];
// Set-->數組
set.toArray(arr);
System.out.println(Arrays.toString(arr));
}
private static void testList2Set() {
List<String> list = new ArrayList<String>();
list.add("ABC");
list.add("EFG");
list.add("LMN");
list.add("LMN");
// List-->Set
Set<String> listSet = new HashSet<String>(list);
System.out.println(listSet);
}
private static void testSet2List() {
Set<String> set = new HashSet<String>();
set.add("AA");
set.add("BB");
set.add("CC");
// Set --> List
List<String> setList = new ArrayList<String>(set);
System.out.println(setList);
}
private static void testList2Array() {
// List-->數組
List<String> list = new ArrayList<String>();
list.add("AA");
list.add("BB");
list.add("CC");
Object[] objects = list.toArray();// 返回Object數組
System.out.println("objects:" + Arrays.toString(objects));
String[] arr = new String[list.size()];
list.toArray(arr);// 將轉化後的數組放入已經創建好的對象中
System.out.println("strings1:" + Arrays.toString(arr));
}
private static void testArray2List() {
// 數組-->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);
}
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