Java 8 – Find the First Element in a List

Introduction

Finding the first element in a list is a common operation in programming, often used when you need to retrieve the initial item in a collection for further processing. Java 8 introduced the Stream API, which provides a streamlined and efficient way to handle such operations. In this guide, we’ll explore how to find the first element in a list using Java 8 Streams, covering both primitive types and custom objects.

Table of Contents

• Problem Statement
• Solution Steps
• Java Program
  • Finding the First Element in a List of Integers
  • Finding the First Element in a List of Strings
  • Finding the First Element in a List of Custom Objects
• Advanced Considerations
• Conclusion

Problem Statement

The task is to create a Java program that:

• Accepts a list of elements.
• Finds the first element in the list.
• Outputs the first element.

Example 1:

• Input: List of integers [1, 3, 7, 0, 5]
• Output: 1

Example 2:

• Input: List of custom Student objects, retrieve the first Student in the list.
• Output: The first Student object.

Solution Steps

1. Input List: Start with a list of elements that can either be hardcoded or provided by the user.
2. Find First Element Using Streams: Use the findFirst() method to retrieve the first element in the list.
3. Display the Result: Print the first element.

Java Program

Finding the First Element in a List of Integers

import java.util.Arrays;
import java.util.List;
import java.util.Optional;

/**
 * Java 8 - Find the First Element in a List of Integers Using Streams
 * Author: https://www.rameshfadatare.com/
 */
public class FindFirstInList {

    public static void main(String[] args) {
        // Step 1: Take input list
        List<Integer> numbers = Arrays.asList(1, 3, 7, 0, 5);

        // Step 2: Find the first element in the list using streams
        Optional<Integer> firstNumber = numbers.stream()
                                               .findFirst();

        // Step 3: Display the result
        firstNumber.ifPresent(num -> System.out.println("First element: " + num));
    }
}

Output

First element: 1

Explanation

• The stream() method is used to create a stream from the list of integers.
• The findFirst() method retrieves the first element in the stream.
• The result is an Optional<Integer>, which is used to safely print the first element.
• The output shows that the first element in the list is 1.

Finding the First Element in a List of Strings

import java.util.Arrays;
import java.util.List;
import java.util.Optional;

/**
 * Java 8 - Find the First Element in a List of Strings Using Streams
 * Author: https://www.rameshfadatare.com/
 */
public class FindFirstStringInList {

    public static void main(String[] args) {
        // Step 1: Take input list
        List<String> fruits = Arrays.asList("apple", "banana", "orange");

        // Step 2: Find the first element in the list using streams
        Optional<String> firstFruit = fruits.stream()
                                            .findFirst();

        // Step 3: Display the result
        firstFruit.ifPresent(fruit -> System.out.println("First fruit: " + fruit));
    }
}

Output

First fruit: apple

Explanation

• The stream() method is used to create a stream from the list of strings.
• The findFirst() method retrieves the first element in the stream.
• The result is an Optional<String>, which is used to safely print the first element.
• The output shows that the first element in the list is "apple".

Finding the First Element in a List of Custom Objects

import java.util.Arrays;
import java.util.List;
import java.util.Optional;

/**
 * Java 8 - Find the First Element in a List of Custom Objects Using Streams
 * Author: https://www.rameshfadatare.com/
 */
public class FindFirstCustomObjectInList {

    public static void main(String[] args) {
        // Step 1: Take input list of custom objects
        List<Student> students = Arrays.asList(
                new Student("Raj", 25),
                new Student("Anita", 30),
                new Student("Vikram", 22)
        );

        // Step 2: Find the first element in the list using streams
        Optional<Student> firstStudent = students.stream()
                                                 .findFirst();

        // Step 3: Display the result
        firstStudent.ifPresent(student -> 
            System.out.println("First student: " + student.getName() + ", Age: " + student.getAge())
        );
    }
}

// Custom class Student
class Student {
    private String name;
    private int age;

    public Student(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }
}

Output

First student: Raj, Age: 25

Explanation

• The list of Student objects is processed to retrieve the first element.
• The findFirst() method is used to get the first Student in the stream.
• The result is an Optional<Student>, which is used to safely print the details of the first Student.
• The output shows that the first Student in the list is "Raj" who is 25 years old.

Advanced Considerations

• Handling Empty Lists: The findFirst() method returns an Optional, which is a safe way to handle cases where the list might be empty. If the list is empty, the Optional will be empty, and you can handle this case appropriately.

• Performance Considerations: Using findFirst() on a stream is efficient and performs well for most lists. If the list is very large and you only need the first element, this method ensures you don’t process the entire list unnecessarily.

• Parallel Streams: While findFirst() works predictably with sequential streams, using it with parallel streams can lead to non-deterministic results depending on how the stream is split and processed. For parallel streams, the result might be the first element in the encounter order, but this isn’t guaranteed.

Conclusion

This guide provides methods for finding the first element in a list using Java 8 Streams, covering both simple lists like integers and strings, as well as more complex lists like custom objects. Java 8 Streams offer a powerful and concise way to perform this operation, making your code more readable and maintainable. Depending on your specific use case, you can easily apply the techniques demonstrated in this guide to retrieve the first element from a list.