java中 List去重的五種方式

 日常開發中經常會使用到list，那么如何更高效的對list進行去重，讓代碼看起來更優雅則需要在實際開發中不斷的優化。推薦還是使用第二種方式，代碼更簡潔一些。
本文的五種去重方式分別是：
1.使用LinkedHashSet刪除arraylist中的重復數據
2.使用java8新特性stream的distinct 進行List去重
3.利用HashSet不能添加重復數據的特性 由於HashSet不能保證添加順序，所以只能作為判斷條件保證順序：
4.利用List的contains方法循環遍歷,重新排序,只添加一次數據,避免重復：
5.雙重for循環去重

1.使用LinkedHashSet刪除arraylist中的重復數據

LinkedHashSet是在一個ArrayList刪除重復數據的最佳方法。LinkedHashSet在內部完成兩件事：

刪除重復數據
保持添加到其中的數據的順序

Java示例使用LinkedHashSet刪除arraylist中的重復項。在給定的示例中，numbersList是包含整數的arraylist，其中一些是重復的數字。

例如1,3和5.我們將列表添加到LinkedHashSet，然后將內容返回到列表中。結果arraylist沒有重復的整數。

import java.util.ArrayList;
import java.util.Arrays;
import java.util.LinkedHashSet;
public class ArrayListExample
{
 public static void main(String[] args)
<span class="token punctuation">{</span>

    ArrayList<span class="token operator">&lt;</span>Integer<span class="token operator">&gt;</span> numbersList <span class="token operator">=</span> <span class="token keyword">new</span> ArrayList<span class="token operator">&lt;</span><span class="token operator">&gt;</span><span class="token punctuation">(</span>Arrays<span class="token punctuation">.</span><span class="token function">asList</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">,</span> <span class="token number">4</span><span class="token punctuation">,</span> <span class="token number">5</span><span class="token punctuation">,</span> <span class="token number">6</span><span class="token punctuation">,</span> <span class="token number">6</span><span class="token punctuation">,</span> <span class="token number">6</span><span class="token punctuation">,</span> <span class="token number">7</span><span class="token punctuation">,</span> <span class="token number">8</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

    System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>numbersList<span class="token punctuation">)</span><span class="token punctuation">;</span>

    LinkedHashSet<span class="token operator">&lt;</span>Integer<span class="token operator">&gt;</span> hashSet <span class="token operator">=</span> <span class="token keyword">new</span> LinkedHashSet<span class="token operator">&lt;</span><span class="token operator">&gt;</span><span class="token punctuation">(</span>numbersList<span class="token punctuation">)</span><span class="token punctuation">;</span>

    ArrayList<span class="token operator">&lt;</span>Integer<span class="token operator">&gt;</span> listWithoutDuplicates <span class="token operator">=</span> <span class="token keyword">new</span> ArrayList<span class="token operator">&lt;</span><span class="token operator">&gt;</span><span class="token punctuation">(</span>hashSet<span class="token punctuation">)</span><span class="token punctuation">;</span>

    System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>listWithoutDuplicates<span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token punctuation">}</span>

}

輸出結果

[1, 1, 2, 3, 3, 3, 4, 5, 6, 6, 6, 7, 8]
[1, 2, 3, 4, 5, 6, 7, 8]

2.使用java8新特性stream進行List去重

要從arraylist中刪除重復項，我們也可以使用java 8 stream api。使用steam的distinct()方法返回一個由不同數據組成的流，通過對象的equals（）方法進行比較。

收集所有區域數據List使用Collectors.toList()。

Java程序，用於在不使用Set的情況下從java中的arraylist中刪除重復項。

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
public class ArrayListExample
 {
 public static void main(String[] args)
<span class="token punctuation">{</span>

    <span class="token builtin">ArrayList</span><span class="token operator">&lt;</span><span class="token builtin">Integer</span><span class="token operator">&gt;</span> numbersList <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ArrayList</span><span class="token operator">&lt;</span><span class="token operator">&gt;</span><span class="token punctuation">(</span><span class="token builtin">Arrays</span><span class="token punctuation">.</span><span class="token function">asList</span><span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">,</span> <span class="token number">4</span><span class="token punctuation">,</span> <span class="token number">5</span><span class="token punctuation">,</span> <span class="token number">6</span><span class="token punctuation">,</span> <span class="token number">6</span><span class="token punctuation">,</span> <span class="token number">6</span><span class="token punctuation">,</span> <span class="token number">7</span><span class="token punctuation">,</span> <span class="token number">8</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token builtin">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>numbersList<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token builtin">List</span><span class="token operator">&lt;</span><span class="token builtin">Integer</span><span class="token operator">&gt;</span> listWithoutDuplicates <span class="token operator">=</span> numbersList<span class="token punctuation">.</span><span class="token function">stream</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">distinct</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">collect</span><span class="token punctuation">(</span><span class="token builtin">Collectors</span><span class="token punctuation">.</span><span class="token function">toList</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

    <span class="token builtin">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>listWithoutDuplicates<span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token punctuation">}</span>

}

輸出結果

[1, 1, 2, 3, 3, 3, 4, 5, 6, 6, 6, 7, 8]
[1, 2, 3, 4, 5, 6, 7, 8]

3.利用HashSet不能添加重復數據的特性由於HashSet不能保證添加順序，所以只能作為判斷條件保證順序：

private static void removeDuplicate(List<String> list) {
    HashSet<String> set = new HashSet<String>(list.size());
    List<String> result = new ArrayList<String>(list.size());
    for (String str : list) {
        if (set.add(str)) {
            result.add(str);
        }
    }
    list.clear();
    list.addAll(result);
}

4.利用List的contains方法循環遍歷,重新排序,只添加一次數據,避免重復：

private static void removeDuplicate(List<String> list) {
    List<String> result = new ArrayList<String>(list.size());
    for (String str : list) {
        if (!result.contains(str)) {
            result.add(str);
        }
    }
    list.clear();
    list.addAll(result);
}

5.雙重for循環去重

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)); 
 } 
}

java中 List去重的五種方式

1.使用LinkedHashSet刪除arraylist中的重復數據

2.使用java8新特性stream進行List去重

3.利用HashSet不能添加重復數據的特性 由於HashSet不能保證添加順序，所以只能作為判斷條件保證順序：

4.利用List的contains方法循環遍歷,重新排序,只添加一次數據,避免重復：

免責聲明！

3.利用HashSet不能添加重復數據的特性由於HashSet不能保證添加順序，所以只能作為判斷條件保證順序：