Java中数组、List、Set互相转换

浅浅的花香味﹌ 2022-05-21 02:10 152阅读 0赞

# 数组转List #

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

*  1
 *  2

*  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
    
     *  1
     *  2
     *  3
 *  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
    
     *  1
     *  2
     *  3
     *  4
     *  5
     *  6

--------------------

# 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

*  1
 *  2
 *  3
 *  4

--------------------

# List转数组 #

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

*  1
 *  2
 *  3
 *  4

--------------------

# List转Set #

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

*  1
 *  2
 *  3
 *  4

--------------------

# Set转数组 #

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

*  1
 *  2
 *  3
 *  4

--------------------

# Set转List #

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

*  1
 *  2
 *  3
 *  4