Java ArrayDeque contains() Method

The ArrayDeque class in Java provides the contains(Object o) method to check if a specific element is present in the deque.

Table of Contents

1. Introduction
2. contains Method Syntax
3. Examples
   • Checking if an Element is Present in the ArrayDeque
   • Handling an Element Not Present in the ArrayDeque
4. Real-World Use Case
   • Use Case: Task Management System
5. Conclusion

Introduction

The ArrayDeque.contains(Object o) method is used to determine whether a specific element is present in the ArrayDeque. This method is useful when you need to verify the presence of an element without removing it from the deque.

contains Method Syntax

The syntax for the contains method is as follows:

public boolean contains(Object o)

• The method takes a single parameter o of type Object, which is the element to check for presence.
• The method returns a boolean value: true if the element is present in the deque, false otherwise.

Examples

Checking if an Element is Present in the ArrayDeque

The contains method can be used to check if a specific element is present in an ArrayDeque.

Example

import java.util.ArrayDeque;

public class ArrayDequeContainsExample {
    public static void main(String[] args) {
        // Creating an ArrayDeque of Strings
        ArrayDeque<String> tasks = new ArrayDeque<>();

        // Adding elements to the ArrayDeque
        tasks.add("Complete project report");
        tasks.add("Email client updates");
        tasks.add("Prepare presentation");

        // Checking if specific elements are present in the ArrayDeque
        boolean containsEmailUpdate = tasks.contains("Email client updates");
        boolean containsTeamMeeting = tasks.contains("Team meeting");

        // Printing the results
        System.out.println("ArrayDeque contains 'Email client updates': " + containsEmailUpdate);
        System.out.println("ArrayDeque contains 'Team meeting': " + containsTeamMeeting);
    }
}

Output:

ArrayDeque contains 'Email client updates': true
ArrayDeque contains 'Team meeting': false

Handling an Element Not Present in the ArrayDeque

When the element is not present in the ArrayDeque, the contains method returns false.

Example

import java.util.ArrayDeque;

public class ElementNotPresentExample {
    public static void main(String[] args) {
        // Creating an ArrayDeque of Strings
        ArrayDeque<String> tasks = new ArrayDeque<>();

        // Adding elements to the ArrayDeque
        tasks.add("Complete project report");
        tasks.add("Email client updates");

        // Checking for an element not present in the ArrayDeque
        boolean containsNonExistentTask = tasks.contains("Non-existent task");

        // Printing the result
        System.out.println("ArrayDeque contains 'Non-existent task': " + containsNonExistentTask);
    }
}

Output:

ArrayDeque contains 'Non-existent task': false

Real-World Use Case

Use Case: Task Management System

In a task management system, you may need to check if a specific task is already in the deque before adding it to avoid duplication. The contains method can help achieve this functionality.

Example

import java.util.ArrayDeque;

public class TaskManagementSystem {
    public static void main(String[] args) {
        // Creating an ArrayDeque to store tasks
        ArrayDeque<Task> tasks = new ArrayDeque<>();

        // Adding initial tasks
        tasks.add(new Task("Complete project report", 2));
        tasks.add(new Task("Email client updates", 1));

        // Checking if a task is already in the deque
        Task newTask = new Task("Complete project report", 2);
        if (tasks.contains(newTask)) {
            System.out.println("Task already exists in the deque: " + newTask);
        } else {
            tasks.add(newTask);
            System.out.println("Task added to the deque: " + newTask);
        }
    }
}

class Task {
    private String description;
    private int priority;

    public Task(String description, int priority) {
        this.description = description;
        this.priority = priority;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        Task task = (Task) o;

        if (priority != task.priority) return false;
        return description != null ? description.equals(task.description) : task.description == null;
    }

    @Override
    public int hashCode() {
        int result = description != null ? description.hashCode() : 0;
        result = 31 * result + priority;
        return result;
    }

    @Override
    public String toString() {
        return description + " (Priority: " + priority + ")";
    }
}

Output:

Task already exists in the deque: Complete project report (Priority: 2)

Conclusion

The ArrayDeque.contains(Object o) method in Java is used for checking the presence of an element in a deque without removing it. Understanding how to use this method can help manage and verify elements in the deque effectively, especially in applications like task management systems where avoiding duplication of tasks is essential.