Java中List，Set，数组的互相转换

Love The Way You Lie 2021-12-09 03:57 319阅读 0赞

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][Java_List_Set]

[Java_List_Set]: https://www.jianshu.com/p/717bc27141c4