Java关于List集合去重方案详细介绍

// 遍历后判断赋给另一个List集合，保持原来顺序
public static void ridRepeat1(List<String> list) {
    System.out.println("list = [" + list + "]");
    List<String> listNew = new ArrayList<String>();
    for (String str : list) {
        if (!listNew.contains(str)) {
            listNew.add(str);
        }
    }
    System.out.println("listNew = [" + listNew + "]");
}

// Set集合去重，保持原来顺序
public static void ridRepeat2(List<String> list) {
    System.out.println("list = [" + list + "]");
    List<String> listNew = new ArrayList<String>();
    Set set = new HashSet();
    for (String str : list) {
        if (set.add(str)) {
            listNew.add(str);
        }
    }
    System.out.println("listNew = [" + listNew + "]");
}

// Set去重     由于Set(HashSet)的无序性，不会保持原来顺序
public static void ridRepeat3(List<String> list) {
    System.out.println("list = [" + list + "]");
    Set set = new HashSet();
    List<String> listNew = new ArrayList<String>();
    set.addAll(list);
    listNew.addAll(set);
    System.out.println("listNew = [" + listNew + "]");
}

// Set通过HashSet去重（将ridRepeat3方法缩减为一行） 无序
public static void ridRepeat4(List<String> list) {
    System.out.println("list = [" + list + "]");
    List<String> listNew = new ArrayList<String>(new HashSet(list));
    System.out.println("listNew = [" + listNew + "]");
}

// Set通过TreeSet去重   会按字典顺序重排序
public static void ridRepeat5(List<String> list) {
    System.out.println("list = [" + list + "]");
    List<String> listNew = new ArrayList<String>(new TreeSet<String>(list));
    System.out.println("listNew = [" + listNew + "]");
}

// Set通过LinkedHashSet去重  保持原来顺序
public static void ridRepeat6(List<String> list) {
    System.out.println("list = [" + list + "]");
    List<String> listNew = new ArrayList<String>(new LinkedHashSet<String>(list));
    System.out.println("listNew = [" + listNew + "]");
}

  //利用java8的stream去重
  List uniqueList = list.stream().distinct().collect(Collectors.toList());
  System.out.println(uniqueList.toString());

// 根据name属性去重
List<User> uniqueNameList = userList
        .stream()
        .collect(collectingAndThen(
                toCollection(() -> new TreeSet<>(comparing(User::getName))), ArrayList::new)
        );

System.out.println("根据name去重后集合元素：" + uniqueNameList.toString());

// 根据name,age属性去重
List<User> uniqueNameAndAgeList = userList
        .stream()
        .collect(collectingAndThen(
                toCollection(() -> new TreeSet<>(comparing(o -> o.getName() + ";" + o.getAge()))), ArrayList::new)
        );

System.out.println("根据name,age去重后集合元素：" + uniqueNameAndAgeList.toString());

//重写equals方法
 @Override
    public boolean equals(Object obj) {
        User user = (User) obj;
        return name.equals(user.getName()) && (age==user.getAge());
    }

//重写hashCode方法
    @Override
    public int hashCode() {
        String str = name + age;
        return str.hashCode();
    }