Learn about the Java LinkedList's `peek()` method. This tutorial covers its syntax, parameters, return value, and provides practical examples.

This reference explains LinkedList peek() method - Syntax and Examples through its syntax, examples and boundaries. Use the linked course lessons when the surrounding Java concepts are unfamiliar.

Java LinkedList peek() method

The peek() method in Java's LinkedList class allows you to examine the first element of the list without removing it. Think of it as a quick glance at what’s at the front, similar to looking at the next card in a deck before deciding whether to play it.

public E peek()

The peek() method retrieves, but does not remove, the first element of this list. It returns null if the list is empty.

The peek() method returns the first element of the list (the head) or null if the list is empty.

This example demonstrates what happens when you try to peek at a list that contains no elements.

import java.util.LinkedList;

public class PeekExample1 {
    public static void main(String[] args) {
        LinkedList<String> myList = new LinkedList<>();

        String firstElement = myList.peek();

        System.out.println("First element: " + firstElement); // Output will be null
    }
}

First element: null

In this case, because the list myList is empty, peek() returns null. This is important to handle in your code – always check for null before trying to use the returned value.

This example shows how to peek at the first element of a list that does contain elements.

import java.util.LinkedList;

public class PeekExample2 {
    public static void main(String[] args) {
        LinkedList<Integer> myList = new LinkedList<>();
        myList.add(10);
        myList.add(20);
        myList.add(30);

        Integer firstElement = myList.peek();

        System.out.println("First element: " + firstElement); // Output will be 10
    }
}

First element: 10

Here, the list contains three integers. The peek() method returns 10, which is the first element added to the list. Crucially, the list itself remains unchanged – the '10' hasn’t been removed.

This example demonstrates peeking at a list containing strings.

import java.util.LinkedList;

public class PeekExample3 {
    public static void main(String[] args) {
        LinkedList<String> myList = new LinkedList<>();
        myList.add("apple");
        myList.add("banana");
        myList.add("cherry");

        String firstElement = myList.peek();

        System.out.println("First element: " + firstElement); // Output will be apple
    }
}

First element: apple

This example works similarly to the previous one, but using strings instead of integers. peek() retrieves “apple” without modifying the list.

Check the example’s types, inputs and documented behavior before copying it into an application. Some APIs require external libraries, files or platform services; consult their setup notes.

Related explanations: Java Data Types - Primitive and Non-Primitive, Java Class - Blueprint of Objects, Exceptions in Java Introduction.

Supporting documentation: Official Java learning guide.