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As a result, code that depends on the remainder operation to always return a positive result is erroneous.

Noncompliant Code Example

This noncompliant code example uses the integer hashKey as an index into the hash array. 

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A negative hash key produces a negative result from the remainder operator, causing the lookup() method to throw java.lang.ArrayIndexOutOfBoundsException.

Compliant Solution

This compliant solution calls the imod() method that always returns a positive remainder:

// Method imod() gives nonnegative result
private int SIZE = 16;
public int[] hash = new int[SIZE];

private int imod(int i, int j) {
  int temp = i % j;
  return (temp < 0) ? -temp : temp; // Unary - will succeed without overflow  
                                    // because temp cannot be Integer.MIN_VALUE
}
	
public int lookup(int hashKey) {
  return hash[imod(hashKey, SIZE)];
}

Applicability

Incorrectly assuming a positive remainder from a remainder operation can result in erroneous code.

Bibliography

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