Java基础|如何查看Java native 方法的实现 Java基础|计算机原理

openJDK上有完整的JDK源代码，JDK源代码由C++、Java、C、汇编这四种语言组成。JVM主体是C++写的，JNI部分是C，工具类是Java写的，JVM里混有汇编代码。路径：openjdk-7-fcs-src-b147\jdk\src\share\native\java\lang\System.c 找到这个
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1 2 3 4 5 6 /* Only register the performance-critical methods */ static JNINativeMethod methods[] = { { "currentTimeMillis" , "()J" ,( void *)&JVM_CurrentTimeMillis}, { "nanoTime" , "()J" ,( void *)&JVM_NanoTime}, { "arraycopy" , "(" OBJ "I" OBJ "II)V" , ( void *)&JVM_ArrayCopy}, };

方法的实现应该在JVM部分，路径openjdk-7-fcs-src-b147\hotspot\src\share，不同的操作系统实现不一样，应该是在对应的操作系统的包下，我在windows目录下找到了纳秒的实现
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1 2 3 4 5 6 7 8 9 10 11 12 jlong os::javaTimeNanos() { if (!has_performance_count) { return javaTimeMillis() * NANOS_PER_MILLISEC; // the best we can do. } else { LARGE_INTEGER current_count; QueryPerformanceCounter(¤t_count); double current = as_long(current_count); double freq = performance_frequency; jlong time = (jlong)((current/freq) * NANOS_PER_SEC); return time ; } }