Java: 数组、列表和集合的互相转换

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。。。

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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：

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3. List 转 Set

 String[] city = {"Nanjing","Shanghai","Beijing"};
 List<String> cityList = Arrays.asList(city);

 Set listToSet = new HashSet(cityList);

　　

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4. Set 转 List

List list = new ArrayList(set);

　　

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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));

　　

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6. Set 转 Array

String[] city = {"Nanjing","Shanghai","Beijing"};
Set set = new HashSet(Arrays.asList(city));
Object[] setToArray = set.toArray();