Array with Constant Time Insertions and Deletions in Java

// Use of Circular Buffer
public class CircularBuffer {

    // Array to store elements
    private int[] buffer;
    private int front;
	private int rear;
	private int size;

    // Constructor to initialize the CircularBuffer with a
    // given capacity
    public CircularBuffer(int capacity)
    {
        // Initialize the buffer
        // array with the
        // specified capacity
        buffer = new int[capacity];

        // Initialize front to -1 (indicating an
        // empty buffer)
        front = -1;

        // Initialize rear to -1 (indicating an
        // empty buffer)
        rear = -1;

        // Initialize size to 0 (indicating an
        // empty buffer)
        size = 0;
    }

    // Method to check if the buffer is empty
    public boolean isEmpty()
    {
        return size == 0;
    }

    // Method to check if the buffer is full
    public boolean isFull()
    {
        return size == buffer.length;
    }

    // Method to insert an element at the start of the
    // buffer
    public void insertAtStart(int value)
    {
        // Check if the buffer is full
        if (isFull()) {
            System.out.println("Buffer is full");
            return;
        }

        // If buffer is empty, set front
        // and rear to 0
        if (isEmpty()) {
            front = 0;
            rear = 0;
        }

        // Otherwise, calculate the new front index
        // using modulo arithmetic
        else {
            front = (front - 1 + buffer.length)
                    % buffer.length;
        }

        buffer[front] = value;
        size++;
    }

    // Method to insert an element at the end of the buffer
    public void insertAtEnd(int value)
    {
        // Check if the buffer is full
        if (isFull()) {
            System.out.println("Buffer is full");
            return;
        }

        // If buffer is empty, set front
        // and rear to 0
        if (isEmpty()) {
            front = 0;
            rear = 0;
        }

        // Otherwise, calculate the new rear index
        // using modulo arithmetic
        else {
            rear = (rear + 1) % buffer.length;
        }

        // Insert the value at the rear
        buffer[rear] = value;

        // Increment the size
        size++;
    }

    // Method to delete an element from the start of the
    // buffer
    public void deleteFromStart()
    {
        if (isEmpty()) { // Check if the buffer is empty
            System.out.println("Buffer is empty");
            return;
        }

        // If buffer has only one element,
        // reset front and rear
        if (size == 1) {
            front = -1;
            rear = -1;
        }
        // Otherwise, calculate the new front index
        // using modulo arithmetic
        else {
            front = (front + 1) % buffer.length;
        }

        // Decrement the size
        size--;
    }

    // Method to delete an element from the end of the
    // buffer
    public void deleteFromEnd()
    {
        // Check if the buffer is empty
        if (isEmpty()) {
            System.out.println("Buffer is empty");
            return;
        }

        // If buffer has only one element,
        // reset front and rear
        if (size == 1) {
            front = -1;
            rear = -1;
        }

        // Otherwise, calculate the new rear index
        // using modulo arithmetic
        else {
            rear = (rear - 1 + buffer.length)
                   % buffer.length;
        }
      	
        size--;
    }

    // Method to display the contents of the buffer
    public void display()
    {
        // Check if the buffer is empty
        if (isEmpty()) {
            System.out.println("Circular Buffer is empty.");
            return;
        }

        System.out.print("Circular Buffer: ");
        int count = 0;
        int index = front;

      	// Iterate over the buffer
        // and print its elements
        while (count < size) {
            System.out.print(buffer[index] + " ");
            index = (index + 1) % buffer.length;
            count++;
        }
        System.out.println();
    }

    public static void main(String[] args)
    {
        CircularBuffer c = new CircularBuffer(5);

        c.insertAtEnd(1);
        c.insertAtEnd(2);
        c.insertAtEnd(3);

        // Output: Circular Buffer: 1 2 3
        c.display();

        c.deleteFromStart();

        // Output: Circular Buffer: 2 3
        c.display();

        c.insertAtStart(4);
        c.insertAtEnd(5);

        // Output: Circular Buffer: 4 2 3 5
        c.display();

        c.deleteFromEnd();

        // Output: Circular Buffer: 4 2 3
        c.display();
    }
}