System.gc () Introduction

System.gc () for the garbage collector, calling the garbage collector will reclaim unused

System.gc () were recovered criteria:

　　Recycling object is not pointing to any variable up

JDK implementation

public static void gc() {
    Runtime.getRuntime().gc();
}

Call the gc method of class Runtime

public native void gc();

Runtime class gc method is a native method, only the code into the JVM to see its true realization

JVM implementation

JNIEXPORT void JNICALL
Java_java_lang_Runtime_gc(JNIEnv *env, jobject this)
{
    JVM_GC();
}

Direct call JVM_GC () method, implemented in the jvm.cpp

This look down, you will find, System.gc () triggers a Full GC

Full GC takes longer, a greater impact on the application, generally do not recommend the use of System.gc ()

In the case of using an external heap memory, the external memory heap if not enough space application, jdk will trigger a System.gc (), to recover

Suggest:

　　Do not use a function gc

　　Keep the code robust (unused variable is set to null), so that virtual machines to manage memory