VarHandle使用

Varhandle 为java9新加功能，用来代替 Unsafe 供开发者使用。直接上代码：

变量定义

    private int plainStr;    //普通变量
    private static int staticStr;    //静态变量
    private int reflectStr;    //通过反射生成句柄的变量
    private int[] arrayStr = new int[]{100, 200, 300};    //数组变量

VarHandle 获取

    private static final VarHandle plainVar;    //普通变量句柄
    private static final VarHandle staticVar;    //静态变量句柄
    private static final VarHandle reflectVar;    //反射字段句柄
    private static final VarHandle arrayVar;    //数组句柄
    static
    {
        try
        {
            MethodHandles.Lookup lookup = MethodHandles.lookup();
            plainVar = lookup.findVarHandle(VarHandleTest.class, "plainStr", int.class);
            staticVar = lookup.findStaticVarHandle(VarHandleTest.class, "staticStr", int.class);
            reflectVar = lookup.unreflectVarHandle(VarHandleTest.class.getDeclaredField("reflectStr"));
            arrayVar = MethodHandles.arrayElementVarHandle(int[].class);
        } catch (ReflectiveOperationException e)
        {
            throw new ExceptionInInitializerError(e);
        }
    }

VarHandle 使用

    public void testVarHandle()
    {
        VarHandleTest test = new VarHandleTest();
        int plainAdd01 = (int)plainVar.getAndAdd(test, 1); //CAS
        int plainAdd02 = (int)plainVar.get(test); //non-volatile
        int staticAdd01 = (int)staticVar.getAndAdd(10); //CAS
        int staticAdd02 = (int)staticVar.get(); //non-volatile
        reflectVar.compareAndSet(test, 0, 5); //CAS
        int reflectSet = (int)reflectVar.get(test); //non-volatile
        arrayVar.compareAndSet(test.arrayStr,0,100,10000); //CAS
        arrayVar.compareAndSet(test.arrayStr,1,200,20000); //CAS

        System.out.println("plainVar01 : " + plainAdd01 +", plainVar02 : " + plainAdd02);
        System.out.println("staticVar01 : " + staticAdd01 +", staticVar02 : " + staticAdd02);
        System.out.println("reflectVar : " + reflectSet);
        System.out.println("arrayVar : " + Arrays.toString(test.arrayStr));
    }

程序运行输出

plainVar01 : 0, plainVar02 : 1
staticVar01 : 0, staticVar02 : 10
reflectVar : 5
arrayVar : [10000, 20000, 300]