Five methods of de duplication in Java list

preface

Weight removal is essential for many occasions. I wrote this article because in a previous picture, I performed distinct and order by de duplication in the database and found that it affected the efficiency, so I did de duplication in the background first; Therefore, this article has been recorded for reference:

Num1: List de duplication using stream, a new feature of java8

public static void main(String[] args) {
    List list = new ArrayList();
    list.add(10);
    list.add(11);
    list.add(14);
    list.add(10);
    list.add(19);
    list.add(12);
    System.out.println("初始化集合为："+list);
    List newList = (List) list.stream().distinct().collect(Collectors.toList());
    System.out.println("java8新特性stream去重后集合为:"+newList);
  }

The result is:

Num2: double for loop de duplication

public static void main(String[] args) {
    List list = new ArrayList();
    list.add(10);
    list.add(11);
    list.add(14);
    list.add(10);
    list.add(19);
    list.add(12);
    System.out.println("初始化集合为："+list);
    for (int i = 0; i < list.size(); i++) {
      for (int j = 0; j < list.size(); j++) {
        if(i!=j&&list.get(i)==list.get(j)) {
          list.remove(list.get(j));
        }
      }
    }
    System.out.println("去重过后新集合为:"+list);
  }

The result is:

Num3: set the judgment to remove the duplicate without disturbing the order

public static void main(String[] args) {
    List list = new ArrayList();
    list.add(10);
    list.add(11);
    list.add(14);
    list.add(10);
    list.add(19);
    list.add(12);
    System.out.println("初始化集合为："+list);
    Set set1 = new HashSet();
    List newList = new ArrayList();
    for (Object integer : list) {
      if(set1.add(integer)) {
        newList.add(integer);
      }
    }
    System.out.println("set集合判断去重:"+newList);
  }

The result is:

Num4: assign to another list set after traversal

public static void main(String[] args) {
    List list = new ArrayList();
    list.add(10);
    list.add(11);
    list.add(14);
    list.add(10);
    list.add(19);
    list.add(12);
    System.out.println("初始化集合为："+list);
    List newList2 = new ArrayList();
    for (Object integer : list) {
      if(!newList2.contains(integer)){
        newList2.add(integer);
      }
    }
    System.out.println("去重后新集合为："+newList2);
  }

The result is:

Num5: set and list conversion de duplication

public static void main(String[] args) {
    List list = new ArrayList();
    list.add(10);
    list.add(11);
    list.add(14);
    list.add(10);
    list.add(19);
    list.add(12);
    System.out.println("初始化集合为："+list);
    Set set2 = new HashSet();
    List newList3 = new ArrayList();
    set2.addAll(list);
    newList3.addAll(set2);
    System.out.println("set和list转换去重:"+newList3);
  }

The result is:

The above is the whole content of this article. I hope it will help you in your study, and I hope you will support us a lot.