List 去重
阿新 • • 發佈:2021-02-20
在日常工作中,需要對 List 進行去重的場景很多。對於我這樣一個菜鳥來說,可能能想到的最簡單粗暴的方法就是雙層迴圈去重,但是在看到這篇文章之後,果斷收藏了。
https://mp.weixin.qq.com/s/N1MRYswi8v1Lh6pdDz8upQ
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既然剛才說到了簡單粗暴的方法,那麼我們就先來看看這種暴力方法:
1.雙層迴圈
import java.util.*; public class ListDemo { private void removeRepeat(List<Integer> listInt) { List<Integer> list = new ArrayList<>(listInt); for (int i = 0; i < list.size(); i++) { for (int j = 0; j < list.size(); j++) { if (i != j && list.get(i).equals(list.get(j))) { list.remove(list.get(j)); } } } System.out.println("去重後的list = " + list); } public static void main(String[] args) { ListDemo listDemo = new ListDemo(); Integer[] array = {1,1,3,5,7,6,4,3,4,5,8,2}; List<Integer> listInt = Arrays.asList(array); System.out.println("去重前的list = " + listInt); listDemo.removeRepeat(listInt); } }
此方法不在乎原 List 中的資料的順序。
2.利用 List 的 contains 方法,遍歷迴圈,重新排序,只新增一次資料
import java.util.*; public class ListDemo { private void removeRepeat(List<Integer> listInt) { List<Integer> list = new ArrayList<>(listInt.size()); for (Integer i : listInt) { if (!list.contains(i)) { list.add(i); } } System.out.println("去重後的list = " + list); } public static void main(String[] args) { ListDemo listDemo = new ListDemo(); Integer[] array = {1,1,3,5,7,6,4,3,4,5,8,2}; List<Integer> listInt = Arrays.asList(array); System.out.println("去重前的list = " + listInt); listDemo.removeRepeat(listInt); } }
這種方法對於 String 型別的 List 同樣適用。
import java.util.*; public class ListDemo { private void removeRepeat(List<String> listStr) { List<String> list = new ArrayList<>(); for (String str : listStr) { if (!list.contains(str)) { list.add(str); } } System.out.println("去重後的list = " + list); } public static void main(String[] args) { ListDemo listDemo = new ListDemo(); String[] array = {"A","B","B","C","A","D","E","C","F","D","G"}; List<String> listStr = Arrays.asList(array); System.out.println("去重前的list = " + listStr); listDemo.removeRepeat(listStr); } }
3.使用 HashSet
利用 HashSet 不能新增重複資料的特性來對 List 進行去重
import java.util.*;
public class ListDemo {
private void removeRepeat(List<String> listStr) {
List<String> list = new ArrayList<>();
HashSet<String> set = new HashSet<>();
for (String str : listStr) {
if (set.add(str)) {
list.add(str);
}
}
System.out.println("去重後的list = " + list);
}
public static void main(String[] args) {
ListDemo listDemo = new ListDemo();
String[] array = {"A","B","B","C","A","D","E","C","F","D","G"};
List<String> listStr = Arrays.asList(array);
System.out.println("去重前的list = " + listStr);
listDemo.removeRepeat(listStr);
}
}
4.使用 java 8 新特性 stream 對 List 進行去重操作
public static void main(String[] args) {
String[] array = {"A","B","B","C","A","G","E","C","F","D","G"};
List<String> listStr = Arrays.asList(array);
System.out.println("去重前的list = " + listStr);
List<String> result = listStr.stream().distinct().collect(Collectors.toList());
System.out.println("去重後的list = " + result);
}
5.使用 LinkedHashSet 來對 List 進行去重操作
public static void main(String[] args) {
String[] array = {"A","B","B","C","A","G","E","C","F","D","G"};
List<String> listStr = Arrays.asList(array);
System.out.println("去重前的list = " + listStr);
LinkedHashSet<String> linkedHashSet = new LinkedHashSet<>(listStr);
List<String> result = new ArrayList<>(linkedHashSet);
System.out.println("去重後的list = " + result);
}
好了,以上就是對 List 去重的幾種方法。對於我來說,平時工作使用的都是 Java 語言,所以我更傾向於使用 Java 8 新特性的 Stream 去進行去重操作。