把下面的类编译好放到ObjectSizeFetcherAgent.jar中

import java.lang.instrument.Instrumentation; public class ObjectSizeFetcher { private static Instrumentation instrumentation; public static void premain(String args, Instrumentation inst) { instrumentation = inst; } public static long getObjectSize(Object o) { return instrumentation.getObjectSize(o); } }

在MANIFEST.MF中加入：

Premain-Class: ObjectSizeFetcher

然后写个test类

public class C { private int x; private int y; public static void main(String [] args) { System.out.println(ObjectSizeFetcher.getObjectSize(new C())); } }

在命令行中这样执行：

java -javaagent:ObjectSizeFetcherAgent.jar C