Efficiently Removing Duplicates from Array , ArrayList and List of Employee using Java 8 Streams

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 Introduction:

In modern Java programming, streams are a powerful tool for working with collections in a concise and efficient way.

Removing Duplicates from Arrays using Java 8 Streams:

Suppose you have an array of integers with duplicates, and you want to create a new array containing only distinct values then follow below steps

1. Convert the array into a stream.
2. Use the distinct() method to eliminate duplicates.
3. Convert the stream back into an array using toArray().

import java.util.Arrays;

public class RemoveDuplicatesFromArray {
    public static void main(String[] args) {
        Integer[] array = {1, 2, 2, 3, 4, 4, 5};

        // Step 1: Convert the array into a stream.
        // Step 2: Use the `distinct()` method to eliminate duplicates.
        // Step 3: Convert the stream back into an array using `toArray()`.
        Integer[] distinctArray = Arrays.stream(array)
                .distinct()
                .toArray(Integer[]::new);

        System.out.println(Arrays.toString(distinctArray));
    }
}

Removing Duplicates from ArrayList using Java 8 Streams:

Suppose you have an ArrayList of strings with duplicates, and you want to create a new ArrayList with distinct values then follow below steps

1. Convert the ArrayList into a stream.
2. Use the distinct() method to remove duplicates.
3. Collect the distinct elements into a new ArrayList using Collectors.toList().

import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;

public class RemoveDuplicatesFromArrayList {
    public static void main(String[] args) {
        List<String> arrayList = new ArrayList<>();
        arrayList.add("apple");
        arrayList.add("banana");
        arrayList.add("apple");
        arrayList.add("cherry");
        arrayList.add("banana");

        // Step 1: Convert the ArrayList into a stream.
        // Step 2: Use the `distinct()` method to remove duplicates.
        // Step 3: Collect the distinct elements into a new ArrayList using `Collectors.toList()`.
        List<String> distinctList = arrayList.stream()
                .distinct()
                .collect(Collectors.toList());

        System.out.println(distinctList);
    }
}

1. Removing Duplicates from List<Employee> using Java 8 Streams:
2. We convert the List of Employee objects into a stream using stream().
3. We use the distinct() method to remove duplicates based on the equals() and hashCode() methods defined in the Employee class.
4. We collect the distinct Employee objects into a new List using Collectors.toList().
5. The resulting distinctEmployees list will contain only unique Employee objects, and you can iterate through it or perform further operations as needed.

import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;

public class RemoveDuplicatesFromEmployeeListWithStreams {
    public static void main(String[] args) {
        List<Employee> employeeList = new ArrayList<>();
        employeeList.add(new Employee(1, "Alice"));
        employeeList.add(new Employee(2, "Bob"));
        employeeList.add(new Employee(1, "Alice")); // Duplicate
        employeeList.add(new Employee(3, "Charlie"));
        employeeList.add(new Employee(2, "Bob")); // Duplicate

        // Step 1: Convert the List of employees into a stream.
        // Step 2: Use the distinct() method to remove duplicates based on equals() and hashCode().
        // Step 3: Collect the distinct elements into a new List using Collectors.toList().
        List<Employee> distinctEmployees = employeeList.stream()
                .distinct()
                .collect(Collectors.toList());

        // Print the distinct Employee objects.
        for (Employee employee : distinctEmployees) {
            System.out.println(employee.getId() + ": " + employee.getName());
        }
    }
}