Java程序从集合中删除所有重复的条目

我们知道HashSet只包含唯一的元素，即不允许有重复的条目，由于我们的目的是将重复的条目从集合中移除，所以为了从集合中移除所有重复的条目，我们将使用HashSet。HashSet类实现了Set接口，由一个哈希表支持，而哈希表实际上是一个HashMap实例。该类还为基本操作提供了恒定的时间性能，如添加、删除、包含和大小，假定哈希函数在桶中正确地分散了元素。HashSet通常被用来检查一个元素是否存在于一个列表中。

注意: 因为我们使用的是HashSet，所以插入的顺序不会被保留，每次我们运行代码的时候都会得到一些不同的输出（元素的顺序会不同）。因此，如果我们想在插入时保留元素的顺序，那么我们应该使用LinkedHashSet。

基本上有两种方法来删除集合中的重复条目。

1.使用哈希集
2.使用LinkHashSet

现在让我们来看看使用java程序的实现，通过使用这两种方法逐一删除重复的条目：-

1.使用HashSet

// Java Program to remove the duplicate entries from
// collection using HashSet
  
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashSet;
  
class GFG {
    public static void main(String[] args)
    {
        // making the collection object
        Collection<String> collection = new ArrayList<>();
  
        // adding the elements to the collection
        collection.add("Geeks");
        collection.add("For");
        collection.add("Geeks");
        collection.add("Internship");
        collection.add("Internship");
        collection.add("2021");
        collection.add("2021");
  
        // Displaying the collection elements
        System.out.println(
            "Displaying the initial collection\n");
        System.out.println(collection);
  
        // HashSEt for deleting duplicate entries
        // in the collection by passing collection
        // in the constructor of the HashSet
        HashSet<String> hashSet = new HashSet<>(collection);
  
        // Displaying the HashSet
        System.out.println("\nDisplaying the HashSet\n");
        System.out.println(hashSet);
  
        // clearing all the elements of the collection
        collection.clear();
  
        // adding all the elements back
        // to the collection from HashSet
        collection.addAll(hashSet);
  
        // Displaying the collection
        System.out.println(
            "\nDisplaying the collection after deleting duplicates entries\n");
        System.out.println(collection);
    }
}

输出:

Displaying the initial collection

[Geeks, For, Geeks, Internship, Internship, 2021, 2021]

Displaying the HashSet

[Geeks, For, 2021, Internship]

Displaying the collection after deleting duplicates entries

[Geeks, For, 2021, Internship]

2.使用LinkedHashSet

// Java Program to remove the duplicate entries from
// collection using LinkedHashSet
  
import java.util.ArrayList;
import java.util.Collection;
import java.util.LinkedHashSet;
  
class GFG {
    public static void main(String[] args)
    {
        // making the collection object
        Collection<String> collection = new ArrayList<>();
  
        // adding the elements to the collection
        collection.add("Geeks");
        collection.add("For");
        collection.add("Geeks");
        collection.add("Internship");
        collection.add("Internship");
        collection.add("2021");
        collection.add("2021");
  
        // Displaying the collection elements
        System.out.println(
            "Displaying the initial collection\n");
        System.out.println(collection);
  
        // LinkedHashSet for deleting duplicate entries
        // in the collection by passing collection
        // in the constructor of the HashSet
        LinkedHashSet<String> hashSet
            = new LinkedHashSet<>(collection);
  
        // Displaying the HashSet
        System.out.println("\nDisplaying the HashSet\n");
        System.out.println(hashSet);
  
        // clearing all the elements of the collection
        collection.clear();
  
        // adding all the elements back
        // to the collection from HashSet
        collection.addAll(hashSet);
  
        // Displaying the collection
        System.out.println(
            "\nDisplaying the collection after deleting duplicates entries\n");
        System.out.println(collection);
    }
}

输出:

Displaying the initial collection 

[Geeks, For, Geeks, Internship, Internship, 2021, 2021] 

Displaying the HashSet 

[Geeks, For, Internship, 2021] 

Displaying the collection after deleting duplicates entries 

[Geeks, For, Internship, 2021]