JAVA Automatic Conversions

Automatic Conversions Java Internals

As per Java language specs ------

 Widening primitive conversions do not lose information about the overall magnitude of a numeric value. Indeed, conversions widening from an integral type to another integral type do not lose any information at all; the numeric value is preserved exactly. Conversions widening from float to double in strictfp expressions also preserve the numeric value exactly; however, such conversions that are not strictfp may lose information about the overall magnitude of the converted value.



    Conversion of an int or a long value to float, or of a long value to double, may result in loss of precision-that is, the result may lose some of the least significant bits of the value. In this case, the resulting floating-point value will be a correctly rounded version of the integer value, using IEEE 754 round-to-nearest mode 

In other words even though you may lose information, you know that the value will still be in the overall range of the target type.



 Widening Primitive Conversion

    The following 19 specific conversions on primitive types are called the widening primitive conversions:

        byte to short, int, long, float, or double
        short to int, long, float, or double
        char to int, long, float, or double
        int to long, float, or double
        long to float or double
        float to double

    Widening primitive conversions do not lose information about the overall magnitude of a numeric value.



    Conversion of an int or a long value to float, or of a long value to double, may result in loss of precision-that is, the result may lose some of the least significant bits of the value. In this case, the resulting floating-point value will be a correctly rounded version of the integer value

To put it another way, the JLS(Java language specification) distinguishes between a loss of magnitude and a loss of precision.

int to byte for example is a (potential) loss of magnitude because you can't store 500 in a byte.

long to float is a potential loss of precision but not magnitude because the value range for floats is larger than that for longs.

So the rule is:

    Loss of magnitude: explicit cast required;
    Loss of precision: no cast required.

• Whatsapp
• Tweet
• Share
• Share
• Share
• Share

Sign up here with your email