Java 數組轉List 以及 List去重,過濾排序分頁 等方法彙總

一、數組轉List

1、Arrays.asList()

List<String> list= new ArrayList<>(Arrays.asList(array));

2、Collections.addAll()

List<String> list = new ArrayList<>(array.length);
Collections.addAll(list,array);

3、List.of()   

Java9新增方法，定義在List接口內，並且爲靜態方法，故可以由類名直接調用

List<String> list = List.of(array);

二、List 去重方法總結

 public static void main(String[] args) {
        List<String> list = new ArrayList<String>();
        list.add("kelly");
        list.add("yzz");
        list.add("hhh");
        list.add("kelly");
        list.add("yzz");
        System.out.println("list"+list);

        //方法一:使用java8新特性stream進行List去重
        List newList = (List) list.stream().distinct().collect(Collectors.toList());
        System.out.println("java8新特性stream去重："+ newList);

        //方法二:set集合判斷去重,不打亂順序
        Set set =new HashSet<>();
        List newList1 = new ArrayList();
        for(String str : list){
            if(set.add(str)){
                newList1.add(str);
            }
        }
        System.out.println("list"+list);
        System.out.println("set集合判斷去重："+newList1);

        //方法三 :遍歷後判斷賦給另一個list集合
        List newList2 = new ArrayList();
        for (String str : list) {
            if(!newList2.contains(str)){
                newList2.add(str);
            }
        }
        System.out.println("list"+list);
        System.out.println("賦值新list去重:"+newList2);

        // 方法四:set和list轉換去重
        Set set2 = new HashSet();
        List newList3 = new ArrayList();
        set2.addAll(list);
        newList3.addAll(set2);
        System.out.println("list"+list);
        System.out.println("set和list轉換去重:" + newList3);

    }

打印結果

list[kelly, yzz, hhh, kelly, yzz]
java8新特性stream去重：[kelly, yzz, hhh]
list[kelly, yzz, hhh, kelly, yzz]
set集合判斷去重：[kelly, yzz, hhh]
list[kelly, yzz, hhh, kelly, yzz]
賦值新list去重:[kelly, yzz, hhh]
list[kelly, yzz, hhh, kelly, yzz]
set和list轉換去重:[yzz, hhh, kelly]

三、List 過濾排序分頁

    public static void main(String[] args) {
        Integer page =1;
        Integer size = 10;
        User user1 = new User("kelly","12345",2);
        User user2 = new User("yzz","26489",1);
        User user3 = new User("meet","25369",1);
        User user4 = new User("yu","120368",2);
        User user5 = new User(null,"120368",null);
        List<User> list = new ArrayList<User>();
        list.add(user1);
        list.add(user2);
        list.add(user3);
        list.add(user4);
        list.add(user5);
        System.out.println("list"+list);

        List list1= list.stream().filter(user-> user.getUsername()==null).collect(Collectors.toList());
        System.out.println("用Stream類過濾username爲空的元素");
        System.out.println(list1);
        List list2= list.stream().filter(user-> user.getUsername()!=null)
                .sorted(Comparator.comparing(User::getUsername))
                .collect(Collectors.toList());
        System.out.println("對username不爲空的元素按照username進行排序");
        System.out.println(list2);
       //然後把兩個結果集合並
        List<User> listAll = new ArrayList<User>();
        listAll.addAll(list1);
        listAll.addAll(list2);
        List<User> collect = listAll.stream().skip((page - 1) * size).limit(size).collect(Collectors.toList());
        System.out.println("通過skip()和limit組合來分頁");
        System.out.println(collect);
    }