需要用到根據gpsTime double類型對List進行去重；
嘗試了倆種辦法，就像知道耗時與性能；

1. 法一：

// 根據gpsTime去重
imagePostList = imagePostList.stream().collect(collectingAndThen(toCollection(() -> new TreeSet<>(comparing(n -> n.getGpsTime()))), ArrayList::new));

2. 法二：

// List遍歷的同時刪除元素需要用Iterator迭代元素，否則會報錯
Set<Double> gpsTimeSet = new HashSet<>();
// 刪除重復的元素
Iterator<ImagePost> iterator = imagePostList.iterator();
while (iterator.hasNext()) {ImagePost imagePost = iterator.next();if (gpsTimeSet.contains(imagePost.getGpsTime())) {log.error("duplicate: id: {}, name: {}, gpsTime: {}", imagePost.getId(), imagePost.getName(), imagePost.getGpsTime());iterator.remove();} else {gpsTimeSet.add(imagePost.getGpsTime());}
}

3. 結果

少量數據發現是 Iterator遍歷刪除效率更高

那么數據量很大的情況下呢？

很明顯，數據量大的時候，還是用Iterator迭代的同時刪除重復元素效率更高一些；
多次運行，效果一致，仍然是Iterator更高效

4. 源代碼

import java.util.*;import static java.util.Comparator.comparing;
import static java.util.stream.Collectors.collectingAndThen;
import static java.util.stream.Collectors.toCollection;/************************************** Class Name: TestRemoveDuplicateGpsTime* Description:〈測試去重gpsTime效率〉* @create 2020/10/16* @since 1.0.0************************************/
public class TestRemoveDuplicateGpsTime {public static void main(String[] args) {TestRemoveDuplicateGpsTime test = new TestRemoveDuplicateGpsTime();test.testEfficency();}public void testEfficency() {List<ImagePost> imagePostList = new ArrayList<>();initImagePost(imagePostList);long time1 = System.currentTimeMillis();// 根據gpsTime去重imagePostList = imagePostList.stream().collect(collectingAndThen(toCollection(() -> new TreeSet<>(comparing(n -> n.getGpsTime()))), ArrayList::new));long time2 = System.currentTimeMillis();System.out.println("當前程序耗時：" + (time2 - time1) + "ms");System.out.println("after GpsTime去重size: " + imagePostList.size());System.out.println("-----------------------------------------------");imagePostList.clear();initImagePost(imagePostList);time1 = System.currentTimeMillis();removeDuplicate(imagePostList);time2 = System.currentTimeMillis();System.out.println("當前程序耗時：" + (time2 - time1) + "ms");}public void removeDuplicate(List<ImagePost> imagePostList) {Set<Double> gpsTimeSet = new HashSet<>();// 刪除重復的元素Iterator<ImagePost> iterator = imagePostList.iterator();while (iterator.hasNext()) {ImagePost imagePost = iterator.next();if (gpsTimeSet.contains(imagePost.getGpsTime())) {System.out.println("duplicate: id: " + imagePost.getId() + ",gpsTime: " + imagePost.getGpsTime());iterator.remove();} else {gpsTimeSet.add(imagePost.getGpsTime());}}System.out.println("after removeDuplicate, count: " + imagePostList.size());}public void initImagePost(List<ImagePost> imagePostList) {imagePostList.add(new ImagePost(1, 11472.15475));imagePostList.add(new ImagePost(2, 11476.1));imagePostList.add(new ImagePost(3, 11475.2));imagePostList.add(new ImagePost(4, 11332.1));imagePostList.add(new ImagePost(5, 11433.5));imagePostList.add(new ImagePost(6, 11472.15475));imagePostList.add(new ImagePost(7, 11476.1));imagePostList.add(new ImagePost(8, 11987.32));}class ImagePost {Integer id;double gpsTime;public ImagePost(Integer id, double gpsTime) {this.id = id;this.gpsTime = gpsTime;}public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public double getGpsTime() {return gpsTime;}public void setGpsTime(double gpsTime) {this.gpsTime = gpsTime;}}
}

參考：

-https://www.cnblogs.com/qq1141100952com/p/11197120.html

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