list,set,map,数组之间的相互转换详细解析

1.list转set
Set set = new HashSet(new ArrayList()); 

2.set转list
List list = new ArrayList(new HashSet());

3.数组转为list
List stooges = Arrays.asList("Larry", "Moe", "Curly");
或者
String[] arr = {"1", "2"};
List list = Arrays.asList(arr);

4.数组转为set
int[] a = { 1, 2, 3 };
Set set = new HashSet(Arrays.asList(a));

5.map的相关操作。
Map map = new HashMap();
map.put("1", "a");
map.put('2', 'b');
map.put('3', 'c');
System.out.println(map);
// 输出所有的值
System.out.println(map.keySet());
// 输出所有的键
System.out.println(map.values());
// 将map的值转化为List
List list = new ArrayList(map.values());
System.out.println(list);
// 将map的值转化为Set
Set set = new HashSet(map.values());
System.out.println(set);

6.list转数组
List list = Arrays.asList("a","b");
String[] arr = (String[])list.toArray(new String[list.size()]);
System.out.println(Arrays.toString(arr));

//1.数组转换为list，map 
String[] arr = {"123","456","789","123"}; 
List<String> list = Arrays.asList(arr); 
//数组转换为map,一维数组时，奇数为key,偶数为value,奇数个元素，最后一个舍掉 
//.二维数组当做两个一维数组 
Map map = MapUtils.putAll(new HashMap(), arr); 

String[][] ss = {{"a","b","e"},{"c","d","f"}}; 
MapUtils.debugPrint(System.out,arr,map); 
MapUtils.putAll(map, arr); 
MapUtils.debugPrint(System.out,arr,map); 
MapUtils.putAll(map, ss); 
MapUtils.verbosePrint(System.out,arr,MapUtils.invertMap(map)); 

//list 转换为arr 
List<String> ls = new ArrayList<String>(); 
ls.add("wch"); 
ls.add("name"); 
String[] as = (String[]) ls.toArray(); 

/**
 * List<Map<Object,Object>> to 二维数组
 * @param list
 * @param keyLength - Map中的key个数
 * @return
 */
public static Object[][] list2array(List<Map<Object,Object>> list,int keyLength){
    Object[][] array = new Object[list.size()][keyLength];
    for(int i=0;i<list.size();i++){
        array[i] = list.get(i).values().toArray();
    }
    return array;
}