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The Java Language Specification allows 64-bit long and double values to be treated as two 32-bit values. For example, a 64-bit write operation could be performed as two separate 32-bit operations.

Wiki MarkupAccording to the _Java Language Specification_, §17§17.7, "Non-Atomic Treatment of {{double}} and {{long}}" \ [[JLS 2005|AA. References#JLS 05]\]:

This behavior is implementation specific; Java virtual machines are free to perform writes to long and double values atomically or in two parts. For the purposes of the Java programming language memory model, a single write to a non-volatile long or double value is treated as two separate writes: one to each 32-bit half. This can result in a situation where a thread sees the first 32 bits of a 64-bit value from one write, and the second 32 bits from another write.

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Bibliography

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[[Goetz 2006AA. References#Goetz 06] ]	3.1.2, Non-atomic 64-Bit Operations
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[[JLS 2005AA. References#JLS 05]]	§17.7, Non-atomic Treatment of double and long ]]></ac:plain-text-body></ac:structured-macro>

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      07. Visibility and Atomicity (VNA)      08. Locking (LCK)