How to get the last element of LinkedHashSet in Java?

Retrieving the last element from a LinkedHashSet in Java means retrieving the last element in its set. Although Java has no built-in method to help retrieve the last item in LinkedHashSets, there are several effective techniques that provide flexibility and convenience to efficiently retrieve this last element without breaking the insertion order - a must for Java developers issues effectively addressed in its application. By effectively applying these strategies into their software projects, they can achieve the best solution for this requirement

LinkedHashSet

LinkedHashSet is an efficient data structure in Java that combines the functions of HashSet and LinkedList data structures to maintain the uniqueness of elements while still retaining their order when inserted.

It is very fast when quickly accessing or changing elements due to the presence of constant time operations like insertion, deletion, retrieval and modification - uses hash tables for fast lookups, while doubly linked lists maintain order for maximum accessibility and efficiency.

This structure is ideal when elements need to be iterated in the order they were added, providing the best iteration order. The iteration order of LinkedHashSet also helps when maintaining the absence of duplicate elements while keeping the insertion order intact.

import java.util.LinkedHashSet;

// ...

LinkedHashSet<datatype> set = new LinkedHashSet<>();
</datatype>

method

Java allows several methods to find the last element from a LinkedHashSet, thus providing access to its last member. There are several ways to do this.

• Convert to ArrayList

• Iterate through LinkedHashSet

• Java 8 Streaming API

Method 1: Convert to ArrayList

ArrayList in Java is a dynamically allocated, resizable array-based implementation of the List interface that provides a flexible and efficient way to store and manipulate elements in a collection.

When elements are added or removed, automatically expand or contract as elements enter or leave. Internally, it maintains an array to store its elements, while supporting various methods of adding, removing, and accessing elements through indexing.

One way to retrieve the last element from a LinkedHashSet is to convert it to an ArrayList via its constructor, which accepts a Collection as an input parameter, and then access and extract its last member from it using its get() method.

algorithm

• Create an empty LinkedHashSet.

• Add elements to LinkedHashSet

• Convert a LinkedHashSet to an ArrayList by creating a new ArrayList using your data as a parameter in its constructor.

• Check the size of an ArrayList.

• If size exceeds zero:

  • Use the get() method of ArrayList and pass index(size-1) as a parameter to access its last element.

  • Now it’s time to take action on our final component.

• Handling the case of size = 0 (meaning the LinkedHashSet is empty) should depend on your specific requirements and considerations.

program

import java.util.ArrayList;
import java.util.LinkedHashSet;

public class LastElementExample {
   public static void main(String[] args) {
      LinkedHashSet<String> linkedSet = new LinkedHashSet<>();
      linkedSet.add("Apple");
      linkedSet.add("Banana");
      linkedSet.add("Orange");
      linkedSet.add("Mango");

      ArrayList<String> arrayList = new ArrayList<>(linkedSet);
      String lastElement = arrayList.get(arrayList.size() - 1);

      System.out.println("Last element: " + lastElement);
   }
}

Output

Last element: Mango

Method 2: Iterate by traversing LinkedHashSet

Java allows the user to iterate through a LinkedHashSet through multiple steps, from creating an empty LinkedHashSet to adding elements. After adding elements, you can use an iterator or a for-each loop to initialize the iteration - iterators can access their objects using the iterator() method inside LinkedHashSet, and for-each loops can use the hasNext() method to check if there are more multi-element

Each iteration, use the next() method to access and retrieve the current element, and update a variable with the value of that element; by the end of the iteration, the variable should contain the last element, and you can use the variable as needed for future operations or processing

algorithm

• Create an empty LinkedHashSet.

• Add elements to LinkedHashSet

• Use an iterator or for-each loop to traverse the LinkedHashSet:

• Use the iterator() method of LinkedHashSet to create an iterator.

• Use a while loop and the hasNext() method to identify if there are more elements.

• Use the next() method in a loop to retrieve the current element.

• Update the value of the current element into the appropriate variable during each iteration

• Once the iteration is complete, the variable will contain its last element.

program

import java.util.Iterator;
import java.util.LinkedHashSet;

public class LastElementExample {
   public static void main(String[] args) {
      LinkedHashSet<Integer> linkedSet = new LinkedHashSet<>();
      linkedSet.add(10);
      linkedSet.add(20);
      linkedSet.add(30);
      linkedSet.add(40);

      Integer lastElement = null;
      Iterator<Integer> iterator = linkedSet.iterator();
      while (iterator.hasNext()) {
         lastElement = iterator.next();
      }

      System.out.println("Last element: " + lastElement);
   }
}

Output

Last element: 40

Method 3: Java 8 Stream API

To get the last element from a LinkedHashSet using Java 8 Stream API, follow the steps below. Create an empty LinkedHashSet, add the elements, convert to a stream using the stream() method, the reduce() terminal operation using the lambda function to return the identity value can reduce the stream to a single element; in this case, the lambda always returns the representation of the current element the second parameter.

最后，当遇到空 LinkedHashSet 时使用 orElse() 方法，并为 orElse() 情况分配默认值（例如 null），然后包含该 LinkedHashSet 中的最后一个元素以进行进一步的处理操作或处理目的。

算法

• 创建一个空的 LinkedHashSet。

• 将元素添加到LinkedHashSet中

• 使用stream()方法将LinkedHashSet转换为Stream

• 利用reduce() 终端操作需要两个参数 - 一个始终返回其第二个参数作为其参数的无限 lambda 函数以及 BinaryOperators 的标识值。

• Reduce 将有效地将数组转换为完整的元素 - 例如，成为 LinkedHashSet 的一部分作为其最终元素。

程序

import java.util.LinkedHashSet;
import java.util.Optional;

public class LastElementExample {
   public static void main(String[] args) {
      LinkedHashSet<String> linkedSet = new LinkedHashSet<>();
      linkedSet.add("Carrot");
      linkedSet.add("Broccoli");
      linkedSet.add("Spinach");
      linkedSet.add("Tomato");

      Optional<String> lastElement = linkedSet.stream().reduce((first, second) -> second);

      if (lastElement.isPresent()) {
         System.out.println("Last vegetable: " + lastElement.get());
      } else {
         System.out.println("LinkedHashSet is empty.");
      }
   }
}

输出

Last vegetable: Tomato

结论

本教程强调了在Java中从LinkedHashSet中检索最后一个元素的有效方法，而不需要专门的方法来完成此任务。通过将其LinkedHashSet转换为ArrayList，并将其索引号作为最后一个元素的索引号进行访问。通过跟踪遇到的最后一个元素来搜索LinkedHashSet可以实现检索

此外，使用 Java 8 的 Stream API 及其归约操作提供了一个优雅的解决方案。这些方法提供了灵活性、效率并维护 LinkedHashSet 的插入顺序。通过转换为 ArrayList、迭代或使用 Java 的 Stream API API，Java 开发人员可以在各种情况下自信地从 LinkedHashSet 中提取最后一个元素。

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