1. Array 转 List
String[] city = {"Nanjing","Shanghai","Beijing"};
List<String> cityList = Arrays.asList(city);
注意：数组转换得到的List大小固定，不能执行add、remove操作，否则会抛出以下异常：
cityList.add("Xiamen");
cityList.remove(2);
如果想控制List大小，只能将Array中的元素依此加入到List当中。。。
2. List 转 Array
Object[] cityArray = cityList.toArray();
for(Object x:cityArray)
System.out.println(x);
注意：因为 List 转换成 Array时，无法获知List内存储的是什么类型数据，所以采用Object类创建数组。运行结果如下：
3. List 转 Set
String[] city = {"Nanjing","Shanghai","Beijing"};
List<String> cityList = Arrays.asList(city);
Set listToSet = new HashSet(cityList);
4. Set 转 List
List list = new ArrayList(set);
5. Array 转 Set
注意：先把Array转换成List，再转换为Set
String[] city = {"Nanjing","Shanghai","Beijing"};
Set set = new HashSet(Arrays.asList(city));
6. Set 转 Array
String[] city = {"Nanjing","Shanghai","Beijing"};
Set set = new HashSet(Arrays.asList(city));
Object[] setToArray = set.toArray();
