Queue.java

/*
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 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package Queue;

 import java.util.Arrays;

/**
 *
 * @author DELL
 * @param <T>
 */
public class Queue<T> implements QueueInterface<T> {
    
    private  T[] array;
    public int head = 0;
    public int tail = 0;
    public int tracker = 0;

    //WHAT DOES THIS DO, WHAT ARE GENERICS
    
    public Queue() {
   
        this.array = (T[]) new Object[10];
    }

    @Override
    public void enqueue(T t) {
        
        //if it is not full
        if(isFull() == false){
            
            //if tail is more than the head but less than the length of the array or its the start of the array
            if((tail > head && tail < array.length) || (tail == 0 && head == 0)){ 
                //add value to tail
                array[tail] = t;
                tail++;
            }
            //if it has reached the end of the array
            else if(tail >= array.length && head > 0){
                tail = 0;
                array[tail] = t;
                tail++;
            }
            
        }
    else{
        //if it is full, increase size of array
        T[] temp = (T[]) new Object[(array.length)*2];

        //loops through array to add the old vx1alues
        //if it started from 0
        if(tail > head){
        
            //copy everything as is
            System.arraycopy(array, 0, temp, 0, array.length);
            array = temp;
            
        }
        else{
            
            int lastIndex = 0;

            for(int i = head ; i < array.length ; i++){
                temp[i] = array[i];
                i++;
                lastIndex = i;
            }
            
            for(int j = 0 ; j < head ; j++){
                lastIndex++;
                temp[lastIndex] = array[j];
                tail = lastIndex++;
            }
            
            array = temp;
            array[tail] = t;
            tail++;
        }
        }
    }
       

    @Override
    public T dequeue() {
        
        //check if it is empty
        if(tracker == 0){
            System.out.println("Sorry, this queue is empty!");
            return null;
        }
        else{
            //if head+1 is more than the length of array
            if(head++ > array.length && tail < head){
                int oldhead = head;
                head = 0;
                tracker--;
                return array[oldhead];
            }
            else{
        //find head remove head
        //then move head to be equal to the next
        //tracker -1
            int oldhead = head;
            head++;
            tracker--;
            return array[oldhead];
            
            }
           
        }
        
        
    }

    @Override
    public T peek() {
        
        return array[head];
    }

    @Override
    public boolean empty() {
        
        return tracker == 0;
 
    }
    
    @Override
    public boolean isFull(){
        
        return tracker != 0 && tail == head;
    }

}

    

queueinterface.java

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package Queue;

/**
 *
 * @author DELL
 * @param <T>
 */
public interface QueueInterface <T> {
    //adds object to the queue, doesnt return anything
    void enqueue(T t);

    //removes head of queue
    T dequeue();

    //checks what object is on top of queue
    T peek();
    //checks if queue is empty, returns boolean
    boolean empty();
    
    boolean isFull();
    
}