Stack implemented by resizing array

public class ResizingArrayStackOfStrings{
    private String[] s;
    private int N;
    public ResizingArrayStackOfStrings(){
        s=new String[1];
        N=0;
    }
    public boolean isEmpty(){
        return N==0;
    }
    public void push(String item){
        if(N==s.length){
            resize(2*s.length);
        }
        s[N++]=item;
    }
    public String pop(){
        if(!isEmpty()){
            String item=s[--N];
            s[N]=null;   //avoid loitering
            if(N<=1/4*s.length){
                resize(1/2*s.length);
            }
            return item;
        }
        else{
            return "the stack is empty";
        }
    }
    public void resize(int size){
        String[] copy=new String[size];
        for(int i=0;i<N;++i){
            copy[i]=s[i]; 
        }
            s=copy;           
    }  
    public int length(){
        return s.length;
    }
}