phplongstring技巧_java unsafe用法解析intlongstring

这里列举一个实例：

实例中列举了int、long、string三种字段的用法。

个中可以看出int占用了4字节，而long占用了8字节，这与java基本类型占用字节数是同等的

1字节： byte , boolean2字节： short , char4字节： int , float8字节： long , double

import sun.misc.Unsafe;import java.lang.reflect.Field;class Car { int intParam = 3; long longParam =5L; String strParam;}public class UnsafeTest { 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 void main(String[] args) throws Exception { Class clazz = Car.class; //获取所有声明字段 Field[] fields = clazz.getDeclaredFields(); System.out.println("开始测试偏移量。
"); //一个实例存在于内存，不同的属性占用不同的内存空间，偏移量便是这个属性所在空间的内存地址 for(Field f : fields){ //获取属性偏移量，可以通过这个偏移量给属性设值 System.out.println(f.getName()+" : "+unsafe.objectFieldOffset(f)); } System.out.println("--------------------------------"); Car car = new Car(); Field intParam = clazz.getDeclaredField("intParam"); int a = (Integer) intParam.get(car); System.out.println("intParam原始值："+a); long intParamOffset = unsafe.objectFieldOffset(intParam); System.out.println("intParam实例变量修正前偏移量："+intParamOffset); //intParam实例变量偏移量是offset 原始值是3，我们要改成10 System.out.println(unsafe.compareAndSwapInt(car, intParamOffset, 3, 10)); System.out.println("intParam改变之后的值："+car.intParam); long intParamOffsetAfter = unsafe.objectFieldOffset(intParam); System.out.println("intParam改变之后偏移量是："+intParamOffsetAfter); System.out.println("------------改为10后，再次调用,返回false--------------------"); System.out.println(unsafe.compareAndSwapInt(car, intParamOffset, 3, 10)); System.out.println("------------开始修正long--------------------"); Field longParam = clazz.getDeclaredField("longParam"); long longInit = (Long) longParam.get(car); System.out.println("longParam原始值："+longInit); long longParamOffset = unsafe.objectFieldOffset(longParam); System.out.println("longParam实例变量的偏移量是："+longParamOffset); System.out.println(unsafe.compareAndSwapLong(car, longParamOffset, 5L, 111L)); System.out.println("longParam改变之后的值："+car.longParam); System.out.println("------------开始修正string--------------------"); Field strParam = clazz.getDeclaredField("strParam"); String str = (String) strParam.get(car); System.out.println("strParam原始值："+str); long strParamOffset = unsafe.objectFieldOffset(strParam); System.out.println("strParam实例变量的偏移量是："+strParamOffset); System.out.println(unsafe.compareAndSwapObject(car, strParamOffset, null, "5")); System.out.println("strParam改变之后的值："+car.strParam); }}

运行结果