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In the Java Hotspot VM (default since JDK 1.2), System.gc() does an explicit garbage collection. Sometimes these calls are buried deep within libraries and are hard to trace. To ignore the call in such cases, use the flag -XX:+DisableExplicitGC. To avoid long pauses while doing a full GC, a less demanding concurrent cycle can be invoked by specifying the flag -XX:ExplicitGCInvokedConcurrent.
One exception There are some exceptions to this rule may existrecommendation. The garbage collector can be explicitly called when the application goes through several phases like the initialization and the ready phase. The heap needs to be compacted between these phases. Given an uneventful period, System.gc() may be explicitly invoked in this case. Also, it may be invoked as a last resort in a catch block to recover from an OutOfMemoryError.
Risk Assessment
Misusing some garbage collection utilities can cause Denial Of Service (DoS) related issues and severe performance degradation.
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