LinkedList contains() method - Syntax and Examples

Learn about the Java LinkedList's `contains()` method, its syntax, parameters, return value, and how to use it with practical examples.

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

The contains() method in Java's LinkedList class is a handy tool to check if a specific element exists within the list. Think of it like searching for something in a drawer – you want to quickly confirm if what you’re looking for is already there.

public boolean contains(Object o)

The contains() method returns a boolean value:

• true: If the list contains the specified element.
• false: If the list does not contain the specified element.

This example demonstrates how to use contains() to see if a specific string is present in a LinkedList of strings.

import java.util.LinkedList;

public class ContainsExample {
    public static void main(String[] args) {
        LinkedList<String> names = new LinkedList<>();
        names.add("Alice");
        names.add("Bob");
        names.add("Charlie");

        String searchName = "Bob";
        boolean containsBob = names.contains(searchName);

        System.out.println("Does the list contain '" + searchName + "'? " + containsBob);
    }
}

Does the list contain 'Bob'? true

Explanation: We create a LinkedList of strings. Then, we use contains() to check if it contains the string "Bob". Since "Bob" is present in the list, the method returns true.

This example shows how to use contains() with a LinkedList of integers.

import java.util.LinkedList;

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

        int searchNumber = 40;
        boolean containsForty = numbers.contains(searchNumber);

        System.out.println("Does the list contain " + searchNumber + '? ' + containsForty); 
    }
}

Does the list contain 40? false

Explanation: We create a LinkedList of integers. We then use contains() to check if it contains the integer 40. Since 40 is not in the list, the method returns false.

This example demonstrates how the LinkedList handles null values when using the contains() method

import java.util.LinkedList;

public class ContainsNullExample {
    public static void main(String[] args) {
        LinkedList<String> strings = new LinkedList<>();
        strings.add("Hello");
        strings.add(null);
        strings.add("World");

        boolean containsNull = strings.contains(null);

        System.out.println("Does the list contain null? " + containsNull); 
    }
}

Does the list contain null? true

Explanation: A LinkedList can contain null values, and contains(null) will return true if a null value is present in 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.