给构造函数为private的类实例化，无视java安全机制

import java.lang.reflect.Field;

import sun.misc.Unsafe;







public class Test {

    public static void main(String[] args) throws Exception{



        Field f1 = Unsafe.class.getDeclaredField("theUnsafe");

        f1.setAccessible(true);

        Unsafe unsafe = (Unsafe) f1.get(null);

        User user = (User) unsafe.allocateInstance(User.class);

        Field f2 = user.getClass().getDeclaredField("name");

        long momoryAddress = unsafe.objectFieldOffset(f2);                    //获取堆外内存地址

        unsafe.putObject(user,unsafe.objectFieldOffset(f2), "xieyong");

        System.out.println(unsafe.getObject(user, momoryAddress));

    }

    

    static class User{

        private User(){

            

        }

        private String name;

        

    }

    

}

    

 原文地址：http://www.cnblogs.com/JimmyXie/p/3780285.html