Possible Duplicate:
Where to find source code for java.lang native methods?
Where can I find Java’s native method implementations of JDK 1.6 Windows platform?
Possible Duplicate:
Where to find source code for java.lang native methods?
Where can I find Java’s native method implementations of JDK 1.6 Windows platform?
Here is how Googles Dalvik VM implements it, I can't imagine the windows or any other version to be much different.
241 /*
242 * static long currentTimeMillis()
243 *
244 * Current time, in miliseconds. This doesn't need to be internal to the
245 * VM, but we're already handling java.lang.System here.
246 */
247 static void Dalvik_java_lang_System_currentTimeMillis(const u4* args,
248 JValue* pResult)
249 {
250 struct timeval tv;
251
252 UNUSED_PARAMETER(args);
253
254 gettimeofday(&tv, (struct timezone *) NULL);
255 long long when = tv.tv_sec * 1000LL + tv.tv_usec / 1000;
256
257 RETURN_LONG(when);
258 }
That depends on which VM you are using. The sources of the Sun / Oracle JDKs can be found here: