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How to Implement a Custom Comparator for a LinkedHashSet in Java?

In Java, we cannot directly implement a custom comparator for a LinkedHashSet. But sometimes we need a requirement of custom comparator for example custom sorting. So, we can use some alternative approaches to fulfill the requirements.

In this article, we will be using a class for creating the custom comparator and this class will implement the Comparable interface for a LinkedHashSet in Java.

Approach:

  • In the first step, we have created a class which is the type of Employee, and implemented a Comparable interface.
  • It accepts a value of Employee type in a constructor and accepts UserIDs.
  • Then Override compareTo method.
  • We also Override a toString method for printing the output.
  • Now we create the LinkedHashSet of type Employee and add Employee ID.
  • Then we add these LinkedHashSet values to an ArrayList.
  • So, we can use Collection.Sort which sorts the elements by User IDs.
  • Then we print the output.

Program to Implement a Custom Comparator for a LinkedHashSet in Java

Suppose we have a LinkedHashSet of Employee IDs and want to perform a custom sorting, for this follow the below implementation.

Java

import java.util.ArrayList;
import java.util.Collections;
import java.util.LinkedHashSet;
import java.util.List;
  
// We need to implement the Comparable interface for creating
// a custom comparator.
class Employee implements Comparable<Employee> {
  
    private int employeeId;
  
    public Employee(int id) {
        this.employeeId = id;
    }
  
    public int getId() {
        return this.employeeId;
    }
  
    // We override the toString method.
    public String toString() {
        return "Employee -> " + getId();
    }
  
    // Custom comparator
    public int compareTo(Employee otherEmployee) {
        return this.getId() - otherEmployee.getId();
    }
}
  
public class GFG {
    public static void main(String[] args) {
        LinkedHashSet<Employee> setOfEmployees = new LinkedHashSet<>();
        setOfEmployees.add(new Employee(3));
        setOfEmployees.add(new Employee(1));
        setOfEmployees.add(new Employee(2));
  
        // Convert the set to a list for sorting
        List<Employee> listUsers = new ArrayList<>(setOfEmployees);
  
        // Sort the list using the custom comparator
        Collections.sort(listUsers);
  
        // Print the sorted list
        System.out.println(listUsers);
    }
}

Output

[Employee -> 1, Employee -> 2, Employee -> 3]

Explanation of the Program:

  • In the above program, we have defined a class Employee that implements the Comparable interface. The compareTo method is implemented to compare Employee objects based on their employee IDs.
  • We create a LinkedHashSet named setOfEmployees to store Employee objects. Note that LinkedHashSet maintains insertion order.
  • We convert the LinkedHashSet to an ArrayList named listUsers to perform sorting. This is done to demonstrate sorting using the custom comparator.
  • We sort the listUsers using Collections.sort method, which uses the custom comparator defined in the Employee class.
  • Finally, we print the sorted list.

 


Reffered: https://www.geeksforgeeks.org

Java

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Category:
 Coding
Sub Category:
 Tutorial
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