Conversions and Promotions - The Java Language Specification - page 84

A widening primitive conversion from float to double that is not strictfp may lose information
about the overall magnitude of the converted value.
A widening 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 (§ 4.2.4 ) .
A widening conversion of a signed integer value to an integral type T simply sign-extends
the two's-complement representation of the integer value to fill the wider format.
A widening conversion of a char to an integral type T zero-extends the representation of the
char value to fill the wider format.
Despite the fact that loss of precision may occur, a widening primitive conversion never
results in a run-time exception (§ 11.1.1 ) .
Example 5.1.2-1. Widening Primitive Conversion
Click here to view code image
class Test {
public static void main(String[] args) {
int big = 1234567890;
float approx = big;
System.out.println(big - (int)approx);
}
}
This program prints:
-46
thus indicating that information was lost during the conversion from type int to type
float because values of type float are not precise to nine significant digits.
5.1.3. Narrowing Primitive Conversion
22 specific conversions on primitive types are called the narrowing primitive conversions :
• short to byte or char
• char to byte or short
• int to byte , short , or char
• long to byte , short , char , or int