1. List转数组

   通过toArray()推荐

   //1. 通过 toArray()
       List<String> list = new ArrayList<>();
       for (int i = 0; i < 10; i++) {
           list.add("value" + i);
       }
       String[] arrays = list.toArray(new String[0]);
       System.out.println(Arrays.toString(arrays));
   }
   

   jdk1.8 stream

   public static void main(String[] args) {
           //2. jdk1.8 stream
           List<String> list = new ArrayList<>();
           for (int i = 0; i < 10; i++) {
               list.add("value" + i);
           }
           String[] arrays = list.stream().toArray(String[]::new);
           System.out.println(Arrays.toString(arrays));
       }
   

2. 数组转List

   Arrays.asList()

   public static void main(String[] args) {
       /*
        * 此种方法生成的List不可进行add和remove操作
        * 因为它是一个定长的List集合，跟数组长度一致
        */
       String[] array = new String[]{"value1", "value2", "value3"};
       List<String> stringList = Arrays.asList(array);
       System.out.println(stringList.toString());
   }
   

   通过Collections.addAll(list, arrays)

   public static void main(String[] args) {
           //2.通过Collections.addAll(list, arrays);
           List<String> stringList=new ArrayList<>();
           String[] array=new String[]{"value1","value2","value3"};
           Collections.addAll(stringList, array);
           System.out.println(stringList.toString());
       }
   

   jdk1.8 通过Stream

   public static void main(String[] args) {
           //3. jdk1.8 通过Stream
           String[] arrays = new String[]{"value1", "value2", "value3"};
           List<String> listStrings = Stream
                   .of(arrays)
                   .collect(Collectors.toList());
           System.out.println(listStrings.toString());
       }
   

3. Set转数组

   通过 toArray()

   private static void setToArray1() {
           Set<String> set = new HashSet<>();
           set.add("value1");
           set.add("value2");
           set.add("value3");
           //Set-->数组
           String[] array=set.toArray(new String[0]);
           System.out.println(Arrays.toString(array));
       }
   

   通过Stream jdk1.8

   private static void setToArray2() {
           Set<String> set = new HashSet<>();
           set.add("value1");
           set.add("value2");
           set.add("value3");
           //Set-->数组
           String[] array= set.stream().toArray(String[]::new);
           System.out.println(Arrays.toString(array));
       }
   

4. 数组转Set

   通过先转List之后引入Set

   //数组-->Set
       private static void arrayToSet() {
           String[] array = {"value1","value2","value3"};
           Set<String> set = new HashSet<>(Arrays.asList(array));
           System.out.println(set);
       }
   

   jdk1.8之后通过Stream

   private static void arrayToSet2() {
           String[] array = {"value1","value2","value3"};
           Set<String> set = Stream.of(array).collect(Collectors.toSet());
           System.out.println(set);
       }
   

5. Set转List

   普遍使用

   //set为null会报错
       private static void setToList() {
           Set<String> set = new HashSet<>();
           set.add("value1");
           set.add("value2");
           set.add("value3");
           set=null;
           List<String> list=new ArrayList<>(set);
           System.out.println(list.toString());
       }
   

   jdk1.8通过Stream

   //效率低不推荐
       private static void setToList2() {
          Set<String> set = new HashSet<>();
           set.add("value1");
           set.add("value2");
           set.add("value3");
           List list=Stream.of(set.toArray(new String[0])).collect(Collectors.toList());
           System.out.println(list.toString());
       }
   

6. List转Set

   //list为null会报错
       private static void listToSet() {
           List<String> list = new ArrayList<>();
           list.add("value1");
           list.add("value2");
           list.add("value3");
           Set<String> set=new HashSet<>(list);
           System.out.println(set.toString());
       }
   

本文转载自简书文章：Java中List，Set，数组的互相转换