Queue implemented by resizing array

public class ResizingArrayQueueOfStrings{
    private String[] s;
    private int tail,head,size;
    public ResizingArrayQueueOfStrings(){
        tail=0;
        head=0;
        size=0;
        s=new String[1];
    }
    public boolean isEmpty(){
        return size==0;
    }
    public int sizeOfQueue(){
        return size;
    }
    public int lengthOfArray(){
        return s.length;
    }
    public void resize(int capacity){
        String[] copy=new String[capacity];
        for(int i=head,j=0;i<size+head;++i){
            copy[j]=s[i%s.length];
            j++;
        }
        head=0;
        tail=size;
        s=copy;
    }
    public void enqueue(String item){
        if(size==s.length){
            resize(2*s.length);           
        }
        s[tail++]=item; 
        tail=tail%s.length;
        size++;
    }
    public String dequeue(){
        if(!isEmpty()){
            String item=s[head];
            s[head++]=null;
            head=head%s.length;
            size--;
            if(size<=s.length/4){
                resize(s.length/2);
            }
            return item;
        } 
        else{
            return "Queue is empty!";
        }
    }
}