Sometimes it is desired to obtain consistent results from floating point operations, across different JVMs and platforms. This guarantee is imposed by the strictfp modifier. On the downside, it is more likely that intermediate operations will overflow or underflow when strictfp is used because the platform specific floating point behavior is disregarded. These issues are This issue is unavoidable when portability is the main concern. The strictfp modifier can be used with a class, method or interface.
Usage | Strictness Behavior |
|---|---|
Class | All code in the class including (instance, variable, static initializers) initializers, code in nested classes |
Method | All code within the method is subject to strictness constraints |
Interface | All code in the class that implements the interface is also strict |
An expression is strict if any of the contained containing classes, methods and or interfaces is defined declared to be a strictfp. Constant expressions containing floating point operations are also evaluated strictly. All compile-time constant expressions are by default, strictfp.
Notably, the strict behavior cannot be inherited by a subclass that extends a strictfp superclass. An overriding method may independently choose to be strictfp when the overridden method is not or vice versa.
Noncompliant Code Example
This noncompliant code example does not enforce the strictfp constraints. Double.MAX_VALUE is being multiplied by 1.1 and reduced back by dividing by 1.1 according to the evaluation order. JVM implementations are not required to report an overflow resulting from the initial multiplication, although they can chose may choose to treat this case as strictfp. The ability to use extended exponent ranges to represent intermediate values is as a result implementation defined.
| Code Block | ||
|---|---|---|
| ||
class Strictfp {
public static void main(String[] args) {
double d = Double.MAX_VALUE;
System.out.println("This value \"" + ((d * 1.1) / 1.1) + "\" cannot be represented as double.");
}
}
|
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To be compliant, use the strictfp modifier within an expression (class, method or interface) to guarantee that intermediate results do not vary due to because of implementation defined compiler optimizations or by design. This code snippet is guaranteed to return positive INFINITY due to because of the intermediate overflow condition.
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