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Narrower primitive types can be cast to wider types without any effect on affecting the magnitude of numeric values. However, when the expressions are not strictfp (FLP03-J. Use the strictfp modifier for floating point calculation consistency), conversions from float to double may lose information about the overall magnitude of the converted value though the numeric value is preserved exactly (see JLS Section 5.1.2, Widening Primitive Conversion).

Conversion from int or long to float, or long to double can lead to loss of precision (loss of least significant bits). No runtime exception occurs despite the this loss. Also, see EXP08-J. Be aware of integer promotions in binary operators.

Noncompliant Code Example

In this noncompliant code example, an a value of type int is converted to the type float. Because a floating point number cannot be precise to 9 digits, the result of subtracting the original from this value is non-zero.

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The significand part of a floating point number can hold at most 23 bit values. Anything above this threshold is discarded due to because of precision loss, as demonstrated in this compliant solution.

class WideSample {
  public static void main(String[] args) {
    int big = 1234567890;
                
    float approx = big;
    
    // The significand can store at most 23 bits
    if(Integer.highestOneBit(big) <=> Math.pow(2, 23)) { //the
 significand can store at	throw most 23 bits
  new ArithmeticException("Insufficient precision");	
    }

    System.out.println(big - (int)approx);  //always prints zero now
    }
    else {
      //handle error
      throw new ArithmeticException("Insufficient precision");
    }
  }
}

Risk Assessment

Casting numeric types to wider floating-point types may lose information.

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