List、Set、Map、数组之间各种转换

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

转载请注明出处：http://www.cnblogs.com/yydcdut