List去重性能比较

/**
     * 使用两个for循环实现List去重(有序)
     *
     * @param list
     */
    public static List removeDuplicationBy2For(List<Temp> list) {
        for (int i = 0; i < list.size(); i++) {
            for (int j = i + 1; j < list.size(); j++) {
                if (list.get(i).equals(list.get(j))) {
                    list.remove(j);
                }
            }
        }
        return list;
    }

    /**
     * 使用List集合contains方法循环遍历(有序)
     *
     * @param list
     */
    public static List removeDuplicationByContains(List<Temp> list) {
        List<Temp> newList = new ArrayList<>();
        for (int i = 0; i < list.size(); i++) {
            boolean isContains = newList.contains(list.get(i));
            if (!isContains) {
                newList.add(list.get(i));
            }
        }
        list.clear();
        list.addAll(newList);
        return list;
    }

    /**
     * 使用HashSet实现List去重(无序)
     *
     * @param list
     */
    public static List removeDuplicationByHashSet(List<Temp> list) {
        HashSet set = new HashSet(list);
        //把List集合所有元素清空
        list.clear();
        //把HashSet对象添加至List集合
        list.addAll(set);
        return list;
    }

    /**
     * 使用TreeSet实现List去重(有序)
     *
     * @param list
     */
    public static List removeDuplicationByTreeSet(List<Temp> list) {
        TreeSet set = new TreeSet(list);
        //把List集合所有元素清空
        list.clear();
        //把HashSet对象添加至List集合
        list.addAll(set);
        return list;
    }

    /**
     * 使用java8新特性stream实现List去重(有序)
     *
     * @param list
     */
    public static List removeDuplicationByStream(List<Temp> list) {
        List newList = list.stream().distinct().collect(Collectors.toList());
        return newList;
    }

    @Test
    public void test() throws IOException {
        List<Temp> list1 = new ArrayList<>();
        List<Temp> list2 = new ArrayList<>();
        List<Temp> list3 = new ArrayList<>();
        List<Temp> list4 = new ArrayList<>();
        List<Temp> list5 = new ArrayList<>();
        Random random = new Random();
        for (int i = 0; i < 10_000; i++) {
            int value = random.nextInt(100);
            list1.add(Temp.builder().age(value).userName(UUID.randomUUID().toString()).build());
            list2.add(Temp.builder().age(value).userName(UUID.randomUUID().toString()).build());
            list3.add(Temp.builder().age(value).userName(UUID.randomUUID().toString()).build());
            list4.add(Temp.builder().age(value).userName(UUID.randomUUID().toString()).build());
            list5.add(Temp.builder().age(value).userName(UUID.randomUUID().toString()).build());
        }
        long startTime;
        long endTime;
        startTime = System.currentTimeMillis();
        removeDuplicationByHashSet(list1);
        endTime = System.currentTimeMillis();
        System.out.println("使用HashSet实现List去重时间:" + (endTime - startTime) + "毫秒");
        startTime = System.currentTimeMillis();
        removeDuplicationByTreeSet(list2);
        endTime = System.currentTimeMillis();
        System.out.println("使用TreeSet实现List去重时间:" + (endTime - startTime) + "毫秒");
        startTime = System.currentTimeMillis();
        removeDuplicationByStream(list3);
        endTime = System.currentTimeMillis();
        System.out.println("使用java8新特性stream实现List去重:" + (endTime - startTime) + "毫秒");
        startTime = System.currentTimeMillis();
        removeDuplicationBy2For(list4);
        endTime = System.currentTimeMillis();
        System.out.println("使用两个for循环实现List去重:" + (endTime - startTime) + "毫秒");
        startTime = System.currentTimeMillis();
        removeDuplicationByContains(list5);
        endTime = System.currentTimeMillis();
        System.out.println("使用List集合contains方法循环遍历:" + (endTime - startTime) + "毫秒");
    }
}

@Data
@Builder
class Temp implements Serializable, Comparable<Temp> {
    private String userName;
    private Integer age;

    @Override
    public int hashCode() {
        return this.userName.hashCode() + this.age.hashCode();
    }

    @Override
    public boolean equals(Object object) {
        if (!(object instanceof Temp)) {
            return false;
        }
        return this.userName.equalsIgnoreCase(((Temp) object).getUserName())
                && this.age.equals(((Temp) object).getAge());
    }

    @Override
    public int compareTo(@NotNull() Temp o) {
        if (o == null) {
            return -1;
        }
        if (this.age >= o.getAge()) {
            return 1;
        }
        return 0;
    }
}

注：HashSet与TreeSet性能最快，相差无几