Map 转 List
/**
* Map 转 List
*/
@Test
public void testMap2List(){
Map<Integer, String> rankMap = new HashMap();
rankMap.put(1, "Java");
rankMap.put(2, "C++");
rankMap.put(3, "Python");
rankMap.put(4, "Php");
List<String> rankList = new ArrayList<>(rankMap.values());
System.out.println(rankList); // [Java, C++, Python, Php]
}
Map 转 Set
/**
* Map 转 Set
*/
@Test
public void testMap2Set(){
Map<Integer, String> rankMap = new HashMap();
rankMap.put(1, "Java");
rankMap.put(2, "C++");
rankMap.put(3, "Python");
rankMap.put(4, "Php");
Set languages = new HashSet(rankMap.values());
System.out.println(languages); // [Java, C++, Php, Python]
}
Array 转 List
/**
* Array 转 List
*/
@Test
public void testArray2List(){
String[] arr = { "Java", "C++", "Php", "Python" };
List<String> list = Arrays.asList(arr);
System.out.println(list); // [Java, C++, Php, Python]
List<String> list2 = Arrays.asList("Dart", "Flutter");
System.out.println(list2); // [Dart, Flutter]
}
Array 转 Set
/**
* Array 转 Set
*/
@Test
public void testArray2Set(){
String[] arr = { "Java", "C++", "Php", "Python" };
Set<String> set = new HashSet(Arrays.asList(arr));
System.out.println(set); // [Java, C++, Php, Python]
}
Set 转 Array
/**
* Set 转 Array
*/
@Test
public void testSet2Array(){
Set<String> set = new HashSet();
set.add("Java");
set.add("Python");
String[] arr = set.toArray(new String[set.size()]);
System.out.println(arr[1]); // Python
}
List 转 Array
/**
* List 转 Array
*/
@Test
public void testList2Array(){
List<String> list = new ArrayList<>();
list.add("Java");
list.add("Python");
String[] strs = list.toArray(new String[0]);
System.out.println(strs[1]); // Python
// 不能直接 List<Integer> 转成 int[] 数组
List<Integer> list2 = new ArrayList<>();
list2.add(1); list2.add(2);
Integer[] nums = list2.toArray(new Integer[0]);
System.out.println(nums[1]); // 2
}
