如何在java中获取对象的内存位置？ [英] How can I get the memory location of a object in java?

问题描述

我想知道JVM分配给放置在系统内存中的对象的位置。

I want to know the location that JVM allocates to objects being placed in the system memory.

推荐答案

这是你的意思可能不想这样做。

This is something you probably don't want to do.

如果真的想要这样做，这样的代码可能会有所帮助：

If you really want to do this, something like this code might help:

package test;

import java.lang.reflect.Field;

import sun.misc.Unsafe;

public class Addresser
{
    private static Unsafe unsafe;

    static
    {
        try
        {
            Field field = Unsafe.class.getDeclaredField("theUnsafe");
            field.setAccessible(true);
            unsafe = (Unsafe)field.get(null);
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
    }

    public static long addressOf(Object o)
    throws Exception
    {
        Object[] array = new Object[] {o};

        long baseOffset = unsafe.arrayBaseOffset(Object[].class);
        int addressSize = unsafe.addressSize();
        long objectAddress;
        switch (addressSize)
        {
            case 4:
                objectAddress = unsafe.getInt(array, baseOffset);
                break;
            case 8:
                objectAddress = unsafe.getLong(array, baseOffset);
                break;
            default:
                throw new Error("unsupported address size: " + addressSize);
        }       

        return(objectAddress);
    }


    public static void main(String... args)
    throws Exception
    {   
        Object mine = "Hi there".toCharArray();
        long address = addressOf(mine);
        System.out.println("Addess: " + address);

        //Verify address works - should see the characters in the array in the output
        printBytes(address, 27);

    }

    public static void printBytes(long objectAddress, int num)
    {
        for (long i = 0; i < num; i++)
        {
            int cur = unsafe.getByte(objectAddress + i);
            System.out.print((char)cur);
        }
        System.out.println();
    }
}

但是

• 无法在JVM或甚至不同版本中移植


• 对象可以随时因GC而移动，并且无法跨GC同步，因此结果可能不会有意义


• 没有在所有体系结构，endianess等测试可能会使这无处不在

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