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Why do I have NullPointerException in my sort implementation?

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梦谈多话
梦谈多话 2021-01-29 07:21

I\'m working on my assignment and I am suppose to create a sort method for my array. However, I\'m getting a null pointer error in my sort method and I\'m not sure why. This is

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  • 心在旅途
    心在旅途 (楼主)
    2021-01-29 08:10

    The cause of NPE is that you store null in your array. The implementation of ComparableTimSort does not check for null. 

     private static void binarySort(Object[] a, int lo, int hi, int start) {
 214         assert lo <= start && start <= hi;
 215         if (start == lo)
 216             start++;
 217         for ( ; start < hi; start++) {
 218             @SuppressWarnings("unchecked")
 219             Comparable pivot = (Comparable) a[start];
 220 
 221             // Set left (and right) to the index where a[start] (pivot) belongs
 222             int left = lo;
 223             int right = start;
 224             assert left <= right;
 225             /*
 226              * Invariants:
 227              *   pivot >= all in [lo, left).
 228              *   pivot <  all in [right, start).
 229              */
 230             while (left < right) {
 231                 int mid = (left + right) >>> 1;
 232                 if (pivot.compareTo(a[mid]) < 0)
 233                     right = mid;
 234                 else
 235                     left = mid + 1;
 236             }
 237             assert left == right;
 238 



    You must assure that null value is not stored in your array. 
    


    To do that you must assert that argument passed in method add is not null and create a copy of your container before sorting to valid size. 
    


    public Object[] sorted() {

    Object[] toSort = Arrays.copyOf(getSetArray(),getSize());
    Arrays.sort(toSort);
    return toSort;
}

    
    
    
             
    
                                                        
    
            
            
    
              
                
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