1、Unsafe知识点整理

2、代码：

package com.javabasic.unsafe;

import java.lang.reflect.Field;

import sun.misc.Unsafe;

/**
 * Unsafe如何使用
 * 
 * 1、使用Unsafe.getUnsafe();获取对象会报错
 * Exception in thread "main" java.lang.ExceptionInInitializerError
Caused by: java.lang.SecurityException: Unsafe
    at sun.misc.Unsafe.getUnsafe(Unsafe.java:90)
    at com.javabasic.unsafe.UnsafeTest1.<clinit>(UnsafeTest1.java:13)
 * 2、插卡源码，只要通过反射获取成员变量theUnsafe即可
 * @author win7
 *
 */
public class UnsafeTest2 {
    
    //获取Unsafe实例对象
    static final Unsafe unsafe;
    
    //变量
    private volatile long state=0;
    
    //记录变量state在类UnsafeTest1中的偏移量
    static final long stateOffset;
    
    static {
        //获取state变量在类UnsafeTest1中的偏移值
        try {
            //使用反射获取Unsafe的成员变量theUnsafe
            Field field = Unsafe.class.getDeclaredField("theUnsafe");
            field.setAccessible(true);
            unsafe = (Unsafe)field.get(null);
            stateOffset = unsafe.objectFieldOffset(UnsafeTest2.class.getDeclaredField("state"));
        } catch (Exception e) {
            System.out.println(e.getLocalizedMessage());
            throw new Error(e);
        }
    }
    
    public static void main(String[] args) {
        UnsafeTest2 unsafeTest1 = new UnsafeTest2();
        boolean compareAndSwapInt = unsafe.compareAndSwapInt(unsafeTest1, stateOffset, 0, 1);
        System.out.println(compareAndSwapInt);
    }

}

3、eclipse中使用Unsafe编译报错

只需要去掉编译校验即可。