小编all*_*rog的帖子

我有一些BLE信标进入深度睡眠模式以节省电池政策.在Android SDK中,是否有可能直接连接(或简单地发现)这些信标并将其唤醒？我需要他们的存在和信号强度.

我希望在值发生变化时收到通知.我正在学习本教程 - > 核心蓝牙简介:构建心率监测器

我用这个蓝牙设备 - > IC卡读卡器(索尼产品)

- (void)viewDidLoad {
    [super viewDidLoad];
    _myCentralManager = [[CBCentralManager alloc] initWithDelegate:self queue:nil];
    [_myCentralManager scanForPeripheralsWithServices:nil options:nil];
    self.myCentralManager = _myCentralManager;
}

#pragma mark - CBCentralManagerDelegate

// method called whenever you have successfully connected to the BLE peripheral
- (void)centralManager:(CBCentralManager *)central didConnectPeripheral:(CBPeripheral *)peripheral
{
    [peripheral setDelegate:self];
    [peripheral discoverServices:nil];
    NSString *connected = [NSString stringWithFormat:@"Connected: %@", peripheral.state == CBPeripheralStateConnected ? @"YES" : @"NO"];
    NSLog(@"%@", connected);
}

// CBCentralManagerDelegate - This is called with the CBPeripheral class as its …

我试图创建一个五个线程,因此如果一个线程在一个对象上调用synchronized方法(在这种情况下是objsyn),那么所有其他线程应该等到线程完成对象.因此输出应该按顺序从线程1到线程5.但输出结果不合时宜.

    class synctest extends Thread
    {
        public synchronized  void  display()
        {
            try{Thread.sleep(5000*((long)(Math.random())));}
            catch(Exception e){}

            System.out.println("From synchornized thread    "+ Thread.currentThread().getName());   
        } 
        public synchronized void run()
        {
            synctest objsyn = new synctest();
            objsyn.display();
        }
        public static void main(String args[])
        {
            synctest objsy = new synctest();
            Thread t1 = new Thread(objsy,"Thread 1");
            Thread t2 = new Thread(objsy,"Thread 2");
            Thread t3 = new Thread(objsy,"Thread 3");
            Thread t4 = new Thread(objsy,"Thread 4");
            Thread t5 = new Thread(objsy,"Thread 5");
            t1.start();
            t2.start();
            t3.start();
            t4.start();
            t5.start();
        }
        }

我正在尝试编写一个返回计算机MAC地址字符串的静态方法(函数本身在这里找到:http://www.mkyong.com/java/how-to-get-mac-address-in-java /).我遇到return了静态功能方面的问题.我得到的错误是missing return statement.我该如何解决这个问题？

static String returnMacAddress(){
        InetAddress ip;
        try{
            ip = InetAddress.getLocalHost();

            NetworkInterface network = NetworkInterface.getByInetAddress(ip);
            byte[] mac = network.getHardwareAddress();

            System.out.print("Current MAC address: ");

            StringBuilder stringBuilder = new StringBuilder();
            for(int i = 0; i < mac.length; i++){
                stringBuilder.append(String.format("%02X%s", mac[i], (i < mac.length - 1) ? "-" : ""));
            }
            return stringBuilder.toString();
        }catch(UnknownHostException e){
            e.printStackTrace();
        } catch(SocketException e){
            e.printStackTrace();
        }
    }

当我们在类中实现接口时,我们需要确保该接口定义的所有方法都出现在类的源代码中.那么为什么这段代码很容易编译？

interface A {
    void f();
}
class X {
    public void f() {}
}
class Y extends X implements A {
}

据我所知,有一些条件可能无法在子类上实现纯虚方法,但可以在没有它的情况下调用子类,从而导致构建错误.

我无法模拟这个.有人对如何实现这一点有任何见解吗？我已经完成了一些搜索,但一直无法进行任何搜索.

我有以下列表:

[1,2,3]
[1]
[1,2,3,4]

从上面,我想生成一个包含以下内容的列表:

[[1,1,1],[1,1,2],[1,1,3],[1,1,4],
[2,1,1], [2,1,2], [2,1,3], [2,1,4],
[3,1,2], [3,1,3],[3,1,4]]

这个过程叫什么？

生成一个pyial列表的阶乘？

是否有内置库可以执行此操作？