Problem No.1

The below program is hideously slow. CAN YOU SPOT THE REASON?

public static void main(String args[]){
      Long sum=0L;
      for ( long i=0; i < Integer.MAX_VALUE; i++){
          sum += i;
      }
      System.out.println(sum);
}

[Click for answer]

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The Correct answer :
Its due to one-character typographical error. The variable sum is declared as Long instead of long, which means that the program constructs about 2^31 unnecessary Long instances. and Changinging the sum from Long to long reduces the runtime of the prg. Therefore the lesson is : Prefer primitives to boxed primitives, and watch out for unintentional autoboxing.