Java中数组、List、Set互相转换

数组转List

String[] staffs = new String[]{
     "Tom", "Bob", "Jane"};
List staffsList = Arrays.asList(staffs);

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需要注意的是， Arrays.asList() 返回一个受指定数组决定的固定大小的列表。所以不能做 add 、 remove 等操作，否则会报错。
```
List staffsList = Arrays.asList(staffs);
staffsList.add("Mary"); // UnsupportedOperationException
staffsList.remove(0); // UnsupportedOperationException
```
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如果想再做增删操作呢？将数组中的元素一个一个添加到列表，这样列表的长度就不固定了，可以进行增删操作。

List staffsList = new ArrayList<String>();
for(String temp: staffs){
  staffsList.add(temp);
}
staffsList.add("Mary"); // ok
staffsList.remove(0); // ok

数组转Set

String[] staffs = new String[]{
     "Tom", "Bob", "Jane"};
Set<String> staffsSet = new HashSet<>(Arrays.asList(staffs));
staffsSet.add("Mary"); // ok
staffsSet.remove("Tom"); // ok

List转数组

String[] staffs = new String[]{
     "Tom", "Bob", "Jane"};
List staffsList = Arrays.asList(staffs);
Object[] result = staffsList.toArray();

List转Set

String[] staffs = new String[]{
     "Tom", "Bob", "Jane"};
List staffsList = Arrays.asList(staffs);
Set result = new HashSet(staffsList);

Set转数组

String[] staffs = new String[]{
     "Tom", "Bob", "Jane"};
Set<String> staffsSet = new HashSet<>(Arrays.asList(staffs));
Object[] result = staffsSet.toArray();

Set转List

String[] staffs = new String[]{
     "Tom", "Bob", "Jane"};
Set<String> staffsSet = new HashSet<>(Arrays.asList(staffs));
List<String> result = new ArrayList<>(staffsSet);