ListQueue

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package QueueClassPractice;

/**
 *
 * @author acer
 */
public class ListQueue {
    Node f;
    Node r;
    int size;

    public ListQueue(){
        f=null;
        r=null;
        size=0;
    }


// The number of items in the queue
    public int size(){
        return size;
    }
// Returns true if the queue is empty
    public boolean isEmpty(){
        if(f==null)
            return true;
        return false;
    }
// Adds the new item on the back of the queue, throwing the
// QueueOverflowException if the queue is at maximum capacity. It
// does not throw an exception for an "unbounded" queue, which
// dynamically adjusts capacity as needed.
    public void enqueue(Object obj) throws QueueOverflowException{
        Node n=new Node(obj,null);
        if(f==null){

            f=n;
            r=n;
        }
        else{
            r.next=n;
            r=n;
        }
            size++;
    }
// Removes the item in the front of the queue, throwing the
// QueueUnderflowException if the queue is empty.
    public Object dequeue() throws QueueUnderflowException{
        Node rn=null;
        Object val=null;
        if(size==0)
            throw new QueueUnderflowException();
        else if(r==f){
            val=f.element;
            rn=f;
            r=null;
            f=null;
        }
        else{
            val=f.element;
            rn=f;
            f=f.next;
        }
        rn.element=null;
        rn.next=null;
        rn=null;
        size--;
        return val;
    }
// Peeks at the item in the front of the queue, throwing
// QueueUnderflowException if the queue is empty.
    public Object peek() throws QueueUnderflowException{
        if(size==0)
            throw new QueueUnderflowException();
        return f.element;
    }
// Returns a textual representation of items in the queue, in the
// format "[ x y z ]", where x and z are items in the front and
// back of the queue respectively.
    public String toString(){
        String str="";
        for(Node n=f;n!=null;n=n.next){
            str+=n.element+" ";
        }
        return "[ "+str+" ]";
    }
// Returns an array with items in the queue, with the item in the
// front of the queue in the first slot, and back in the last slot.
    public Object[] toArray(){
        Object[]temp=new Object[size()];
        int i=0;
        for(Node n=f;n!=null;n=n.next){
            temp[i]=n.element;
            i++;
        }
        return temp;
    }
// Searches for the given item in the queue, returning the
// offset from the front of the queue if item is found, or -1
// otherwise.
    public int search(Object obj){
        int count=0;
        for(Node n=f;n!=null;n=n.next){
            if(obj.equals(n.element)){
                return count;
            }
            count++;
        }
        return -1;
    }

}