如何通过引用获取对象的大小？

import java.lang.instrument.Instrumentation;

public class ObjectSizeFetcher {
    private static Instrumentation instrumentation;

    public static void premain(String agentArgs, Instrumentation inst) {
        instrumentation = inst;
    }

    public static long getObjectSize(Object obj) {
        if (instrumentation == null) {
            throw new IllegalStateException("Instrumentation not initialized");
        }
        return instrumentation.getObjectSize(obj);
    }
}

public class Main {
    public static void main(String[] args) {
        Object obj = new Object();
        long size = ObjectSizeFetcher.getObjectSize(obj);
        System.out.println("Object size: " + size + " bytes");
    }
}