Queue Example in Java

Introduction

Queue is a classic Java console program that demonstrates the concept with complete source code and sample output. Classic data structures such as stack, queue and linked list implemented in Java.

This tutorial walks through the program line by line, explains how the logic works, and highlights best practices you can apply in your own code.

Definition

In each of the cases, the customer or object at the front of the line was the first one to enter, while at the end of the line is the last to have entered. Every time a customer finishes paying for their items (or a person steps off the escalator, or the machine part is removed from the assembly line, etc.) that object leaves the queue from the front. This represents the queue ?dequeue? function. Every time another object or customer enters the line to wait, they join the end of the line and represent the ?enqueue? function. The queue ?size? function would return the length of the line, and the ?empty? function would return true only if there was nothing in the line.

Queue Example Program

import java.io.IOException;
import java.util.LinkedList;
import java.util.Queue;

public class QueueExample {

    public static void main(String arg[]) throws IOException {
        Queue q = new LinkedList();
        
        // Add in Queue
        q.add(23);
        q.add(33);
        System.out.println(q);
        System.out.println("Queue Element :"+q.element());
        // Offer In Queue 
        q.offer(34);
        q.offer(98);
        q.offer(77);

        System.out.println(q);
        System.out.println("Queue Element :"+q.element());
        q.poll();
        System.out.println("Queue Element :"+q.element());
        System.out.println("After poll : " + q);
    }
}

Sample Output

[23, 33]
Queue Element :23
[23, 33, 34, 98, 77]
Queue Element :23
Queue Element :33
After poll : [33, 34, 98, 77]

When to use

Use this queue example when learning or revising core Java syntax.

How it works

1. Execution begins in the main method — the JVM calls this method when you run the class.

2. import java.io.IOException; imports a class used later in the program.

3. import java.util.LinkedList; imports a class used later in the program.

4. import java.util.Queue; imports a class used later in the program.

5. Queue q = new LinkedList(); updates a variable used in the calculation or output.

6. A println / print call writes text to the console — part of the sample output below.

7. A println / print call writes text to the console — part of the sample output below.

8. A println / print call writes text to the console — part of the sample output below.

Best Practices

• Use meaningful variable and class names that describe their purpose.
• Compile and run the program locally — modify values to see how output changes.
• Read compiler errors carefully; they usually point to the exact line to fix.

Common Mistakes

• Copying code without understanding each line — practice by changing one statement at a time.
• Mismatching the public class name and the .java filename.
• Forgetting semicolons at the end of statements.