刚学Java不久的时候，接到一个电面，然后问了一些java的知识，比如说Java的编码，Unicode等，但是最让我蛋疼的是怎么吗map转为set，那个时候对集合用的很少，对集合不是特别了解，map还知道，set就蒙了，然后转为set更蒙了，觉得应该有API提供吧，但是不知道怎么说。后来我一直下来再查这个问题，查到了，但是没有实践过，今天我就来一发代码。
List转Set
Set set = new HashSet(new ArrayList());
Set转List
List list = new ArrayList(new HashSet());
数组转为List
List arr = Arrays.asList("1", "2", "3");
//或者
String[] arr = {"1", "2"};
List list = Arrays.asList(arr);
数组转为Set
int[] arr = { 1, 2, 3 }; Set set = new HashSet(Arrays.asList(arr));
Map的值转化为List
List list = new ArrayList(map.values());
Map的值转化为Set
Set set = new HashSet(map.values());
List转数组
List list = Arrays.asList("a","b");
String[] arr = (String[])list.toArray(new String[list.size()]);
代码
public class listsetmao { private static List<String> arrayList; private static Map<String, String> hashMap; private static Set<String> hashSet; private static String[] arr = {"11oneone","22twotwo"}; public static void main(String[] args) { /* * //list转set initList(); Set<String> set = new * HashSet<String>(arrayList); * System.out.println("arrayList.toString()--->"+set.toString()); * System.out.println("set.toString()--->"+set.toString()); */ /* * //set转list initSet(); List<String> list = new * ArrayList<String>(hashSet); * System.out.println("hashSet.toString()--->"+hashSet.toString()); * System.out.println("list.toString()--->"+list.toString()); */ /* // 数组转为list List<String> list = Arrays.asList(arr); System.out.println("list.toString()--->"+list.toString()); */ /* //数组转set Set set = new HashSet<>(Arrays.asList(arr)); System.out.println("set.toString()--->"+set.toString()); */ /* //map的值转为list initMap(); List<String> list = new ArrayList<String>(hashMap.values()); System.out.println("list.toString()--->"+list.toString()); */ /* //map的值转为set initMap(); Set<String> set = new HashSet<String>(hashMap.values()); System.out.println("set.toString()--->"+set.toString()); */ /* //map的key转为set initMap(); Set<String> set = new HashSet<String>(hashMap.keySet()); System.out.println("set.toString()--->"+set.toString()); */ //list转数组 initList(); String[] arr1 = (String[])arrayList.toArray(new String[arrayList.size()]); System.out.println("Arrays.toString(arr1)--->"+Arrays.toString(arr1)); } public static void initList() { arrayList = new ArrayList<String>(); arrayList.add("1"); arrayList.add("2"); arrayList.add("3"); arrayList.add("4"); } public static void initMap() { hashMap = new HashMap<String, String>(); hashMap.put("one", "one1"); hashMap.put("two", "two2"); hashMap.put("three", "three3"); } public static void initSet() { hashSet = new HashSet<String>(); hashSet.add("1one"); hashSet.add("2two"); hashSet.add("3three"); hashSet.add("4four"); hashSet.add("5five"); } }
我是天王盖地虎的分割线
源代码：http://pan.baidu.com/s/1dD1Qx01
listsetmap.zip
本文转自我爱物联网博客园博客，原文链接：http://www.cnblogs.com/yydcdut/p/3825721.html如需转载请自行联系原作者
