FULL PRODUCT VERSION :
java version "1.8.0_31"
Java(TM) SE Runtime Environment (build 1.8.0_31-b13)
Java HotSpot(TM) 64-Bit Server VM (build 25.31-b07, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows [Version 6.3.9600]

A DESCRIPTION OF THE PROBLEM :
In the package java.util.stream, the classes DoubleStream, LongStream, IntStream all provide a "sum()" method. However, it may be impossible to retrieve the exact sum with these methods:
IntStream and LongStream are subject to overflow & may thus even return a negative result
DoubleStream provides a reasonable result, but is inherently not precise when the result gets too big

In my opinion, the javadoc of the sum-related methods should be updated:
for IntStream:
* refer to the method "summaryStatistics()", since the getSum() of IntSummaryStatistics returns long (instead of "int" from the sum() of IntStream, so overflow is already much more unlikely)

for IntStream/LongStream:
* warn about overflow

for IntStream/LongStream/DoubleStream:
* an example of how to do an exact summing reduction
for IntStream/LongStream: stream.boxed().map(BigInteger::valueOf).reduce(BigInteger.ZERO, BigInteger::add);
for DoubleStream: stream.boxed().map(BigDecimal::valueOf).reduce(BigDecimal.ZERO, BigDecimal::add);

* a warning about the trade-off between robustness & performance: there's no use in doing an exact reduction if you know for a fact that overflow cannot occur



REPRODUCIBILITY :
This bug can be reproduced always.