algorithm - Java-Randomized Queue Iterator Causes Invalid Range Exception -

i have implementation of randomized queue in java. although enqueue, dequeue , sample operations work fine, iterator causes invalid range exception thrown every time in shuffle method.

i not understand why since random number generation in shuffle() method bound size of queue. here code:

private int n=0; private item[] queue; public randomizedqueue(){    queue= (item[]) new object[8]; }                // construct empty randomized queue public boolean isempty(){    return n==0; }                 // queue empty? public int size(){    return n; }// return number of items on queue private void resize(int capacity){     item[] copy=(item[]) new object[capacity];     for(int i=0;i<n;i++){         copy[i]=queue[i];     }     queue=copy; }  private class queueiterator implements iterator<item>{     int i=0;     public queueiterator(){         if(n>0){             shuffle();         }     }     @override     public boolean hasnext() {         return i<n;     }      @override     public item next() {         item item=queue[i];         i++;         return item;     }      @override     public void remove() {         throw new java.lang.unsupportedoperationexception("remove not supported");     }  }  public void enqueue(item item){     if(item==null){         throw new java.lang.nullpointerexception("can't insert null items");      }      if(n==queue.length){         resize(2*queue.length);     }     queue[n++]=item; }           // add item public item dequeue(){     if(isempty()){         throw new java.util.nosuchelementexception("queue empty");     }     int i=stdrandom.uniform(0, n);     item item=queue[i];     exchange(i,n-1);     n=n-1;     queue[n]=null;     return item; }                    // remove , return random item public item sample(){     if(isempty()){         throw new java.util.nosuchelementexception("queue empty");     }     int i=stdrandom.uniform(0,n);     return queue[i]; }                     // return (but not remove) random item public iterator<item> iterator(){    return new queueiterator(); }         // return independent iterator on items in random order private void exchange( int i, int j){     item swap=queue[i];     queue[i]=queue[j];     queue[j]=swap; }  private void shuffle(){     for(int i=0;i<n;i++){         int j=stdrandom.uniform(0, i);         exchange(i,j);     } } 

in method shuffle():

private void shuffle(){     for(int i=0;i<n;i++){         int j=stdrandom.uniform(0, i);         exchange(i,j);     } } 

in first iteration, when call stdrandom.uniform(0, 0), throws exception because second argument must strictly greater first. should change for loop minimum value i 1.

from documentation:

uniform

public static int uniform(int a, int b)

returns integer uniformly in [a, b).

throws:

illegalargumentexception - if b <= a

illegalargumentexception - if b - >= integer.max_value