The new I/O (NIO) classes in java.nio allow the creation and use of direct buffers. These buffers tremendously increase throughput for repeated I/O activities. However, their creation and reclamation is more expensive than the creation and reclamation for of heap-based nondirect buffers because direct buffers are managed using OS-specific native code. This added management cost makes direct buffers a poor choice for single-use or infrequently used cases. Direct buffers are also not subject to outside the scope of Java's garbage collector, which can cause memory leaks. Frequent allocation of large direct buffers can cause an OutOfMemoryError.

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This noncompliant code example uses both a short-lived local object rarelyUsedBuffer and a long-lived heavily used object heavilyUsedBuffer. Both are allocated in nonheap memory, and ; neither is garbage collected.

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Applicability

Direct buffers are not subject to beyond the scope of Java's garbage collector, which can cause memory leaks if they are used injudiciously. In general, direct buffers should be allocated only when it can be shown that their use provides a significant gain in performance.

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