我在init（）方法中尝试了catch块。 但我想把它们扔向消费阶层。
但是，如果我删除try catch块并为该方法添加throws声明。 我必须为构造函数和getInstance方法添加它。
但是再次运行我的应用程序会让我在删除try catch块的地方出错。 我之前没有遇到过这些错误。 对于异常抛出的其他方法，没有在构造函数中调用，没有问题。
知道如何正确处理这个问题吗？提前谢谢。
我也已经看过这里：Singleton and Exception
但它没有帮助。
public class Communicator {
private static Communicator instance = null;
protected Communicator() {
init();
}
public static Communicator getInstance() {
if (instance == null) {
instance = new Communicator();
}
return instance;
}
public void init() {
// set up connections
}
}
好的，因为需要更多细节：这是完整的代码，没有额外的方法可以抛出异常=＆gt;
public class WindowsMidiCommunicator {
private MidiDevice.Info[] devices;
private MidiDevice outputDevice = null;
private Receiver recvr = null;
private MidiDevice inputDevice = null;
private Transmitter trans = null;
private DumpReceiver outputReceiverDump;
private Logger log;
private MessageQueue<Message> queue = null;
private static WindowsMidiCommunicator instance=null;
protected WindowsMidiCommunicator() {
init();
}
public static WindowsMidiCommunicator getInstance(){
if(instance==null){
instance=new WindowsMidiCommunicator();
}
return instance;
}
public void init() {
devices = MidiSystem.getMidiDeviceInfo();
outputReceiverDump = new DumpReceiver(System.out);
queue = new MessageQueue<Message>();
outputReceiverDump.setMessageQueue(queue);
Logger log = LogManager.getLogger(Saffiretest.class.getName());
for (MidiDevice.Info info : devices) {
if (info.getName().contains("Saffire")) {
MidiDevice device = null;
try {
device = MidiSystem.getMidiDevice(info);
} catch (MidiUnavailableException e1) {
log.error("MidiUnavailableException");
e1.printStackTrace();
}
if (!device.isOpen()) {
try {
device.open();
} catch (MidiUnavailableException e) {
log.error("MidiUnavailableException");
e.printStackTrace();
}
}
if (device instanceof Sequencer) {
log.info("Device is a Sequencer");
}
if (device instanceof Synthesizer) {
log.info("Device is a Synthesizer");
}
log.info("Max receivers:" + device.getMaxReceivers());
if (device.getMaxReceivers() == -1) {
outputDevice = device;
log.info(device.getDeviceInfo().getName()
+ "obtained as outputDevice");
}
if (device.getMaxTransmitters() == -1) {
inputDevice = device;
log.info(device.getDeviceInfo().getName()
+ "obtained as inputDevice");
}
log.info("Max transmitters:" + device.getMaxTransmitters());
log.info("Open receivers:");
List<Receiver> receivers = device.getReceivers();
for (Receiver r : receivers) {
log.info(r.toString());
}
try {
log.info("Default receiver: "
+ device.getReceiver().toString());
log.info("Open receivers now:");
receivers = device.getReceivers();
for (Receiver r : receivers) {
log.info(r.toString());
}
} catch (MidiUnavailableException e) {
log.info("No default receiver");
}
log.info("Open transmitters:");
List<Transmitter> transmitters = device.getTransmitters();
for (Transmitter t : transmitters) {
log.info(t.toString());
}
try {
log.info("Default transmitter: "
+ device.getTransmitter().toString());
log.info("Open transmitters now:");
transmitters = device.getTransmitters();
for (Transmitter t : transmitters) {
log.info(t.toString());
}
} catch (MidiUnavailableException e) {
log.error("No default transmitter");
}
}
}
try {
recvr = outputDevice.getReceiver();
} catch (MidiUnavailableException e) {
log.error("no receiver available");
e.printStackTrace();
}
try {
trans = inputDevice.getTransmitter();
trans.setReceiver(outputReceiverDump);
} catch (MidiUnavailableException e) {
log.error("no transmitter available");
e.printStackTrace();
}
}
现在当删除所有这些尝试catch块时，我最终将会这样：
protected WindowsMidiCommunicator() throws MidiUnavailableException {
init();
}
public static WindowsMidiCommunicator getInstance() throws MidiUnavailableException{
if(instance==null){
instance=new WindowsMidiCommunicator();
}
return instance;
}
public void init() throws MidiUnavailableException {
devices = MidiSystem.getMidiDeviceInfo();
outputReceiverDump = new DumpReceiver(System.out);
queue = new MessageQueue<Message>();
outputReceiverDump.setMessageQueue(queue);
Logger log = LogManager.getLogger(Saffiretest.class.getName());
for (MidiDevice.Info info : devices) {
if (info.getName().contains("Saffire")) {
MidiDevice device = null;
device = MidiSystem.getMidiDevice(info);
if (!device.isOpen()) {
device.open();
}
if (device instanceof Sequencer) {
log.info("Device is a Sequencer");
}
if (device instanceof Synthesizer) {
log.info("Device is a Synthesizer");
}
log.info("Max receivers:" + device.getMaxReceivers());
if (device.getMaxReceivers() == -1) {
outputDevice = device;
log.info(device.getDeviceInfo().getName()
+ "obtained as outputDevice");
}
if (device.getMaxTransmitters() == -1) {
inputDevice = device;
log.info(device.getDeviceInfo().getName()
+ "obtained as inputDevice");
}
log.info("Max transmitters:" + device.getMaxTransmitters());
log.info("Open receivers:");
List<Receiver> receivers = device.getReceivers();
for (Receiver r : receivers) {
log.info(r.toString());
}
log.info("Default receiver: "
+ device.getReceiver().toString());
log.info("Open receivers now:");
receivers = device.getReceivers();
for (Receiver r : receivers) {
log.info(r.toString());
}
log.info("Open transmitters:");
List<Transmitter> transmitters = device.getTransmitters();
for (Transmitter t : transmitters) {
log.info(t.toString());
}
log.info("Default transmitter: "
+ device.getTransmitter().toString());
log.info("Open transmitters now:");
transmitters = device.getTransmitters();
for (Transmitter t : transmitters) {
log.info(t.toString());
}
}
}
recvr = outputDevice.getReceiver();
trans = inputDevice.getTransmitter();
trans.setReceiver(outputReceiverDump);
}
这是主要方法：
public static void main(String[] args) {
try {
WindowsMidiCommunicator.getInstance().testConnectivity();
} catch (InvalidMidiDataException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (MidiUnavailableException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
try {
WindowsMidiCommunicator.getInstance().sendCurrentPresetRequest();
} catch (InvalidMidiDataException | MidiUnavailableException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
new java.util.Timer().schedule(
new java.util.TimerTask() {
@Override
public void run() {
try {
WindowsMidiCommunicator.getInstance().closeDevices();
} catch (MidiUnavailableException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
},
5000
);
}
运行时，这是堆栈跟踪：
INFO ] 2015-05-05 11:08:32.572 [main] Saffiretest - Max receivers:0
javax.sound.midi.MidiUnavailableException: MIDI IN receiver not available
at com.sun.media.sound.AbstractMidiDevice.createReceiver(Unknown Source)
at com.sun.media.sound.AbstractMidiDevice.getReceiver(Unknown Source)
at WindowsMidiCommunicator.init(WindowsMidiCommunicator.java:79)
at WindowsMidiCommunicator.<init>(WindowsMidiCommunicator.java:28)
at WindowsMidiCommunicator.getInstance(WindowsMidiCommunicator.java:32)
at SafferOrganizedTest.main(SafferOrganizedTest.java:9)
[INFO ] 2015-05-05 11:08:32.573 [main] Saffiretest - 2- Saffire 6USBobtained as inputDevice
[INFO ] 2015-05-05 11:08:32.574 [main] Saffiretest - Max transmitters:-1
[INFO ] 2015-05-05 11:08:32.574 [main] Saffiretest - Open receivers:
[INFO ] 2015-05-05 11:08:32.577 [main] Saffiretest - Max receivers:0
[INFO ] 2015-05-05 11:08:32.577 [main] Saffiretest - 2- Saffire 6USBobtained as inputDevice
[INFO ] 2015-05-05 11:08:32.577 [main] Saffiretest - Max transmitters:-1
[INFO ] 2015-05-05 11:08:32.577 [main] Saffiretest - Open receivers:
javax.sound.midi.MidiUnavailableException: MIDI IN receiver not available
at com.sun.media.sound.AbstractMidiDevice.createReceiver(Unknown Source)
at com.sun.media.sound.AbstractMidiDevice.getReceiver(Unknown Source)
at WindowsMidiCommunicator.init(WindowsMidiCommunicator.java:79)
at WindowsMidiCommunicator.<init>(WindowsMidiCommunicator.java:28)
at WindowsMidiCommunicator.getInstance(WindowsMidiCommunicator.java:32)
at SafferOrganizedTest.main(SafferOrganizedTest.java:18)
[INFO ] 2015-05-05 11:08:37.583 [Timer-0] Saffiretest - Max receivers:0
javax.sound.midi.MidiUnavailableException: MIDI IN receiver not available
[INFO ] 2015-05-05 11:08:37.584 [Timer-0] Saffiretest - 2- Saffire 6USBobtained as inputDevice
[INFO ] 2015-05-05 11:08:37.584 [Timer-0] Saffiretest - Max transmitters:-1
[INFO ] 2015-05-05 11:08:37.584 [Timer-0] Saffiretest - Open receivers:
at com.sun.media.sound.AbstractMidiDevice.createReceiver(Unknown Source)
at com.sun.media.sound.AbstractMidiDevice.getReceiver(Unknown Source)
at WindowsMidiCommunicator.init(WindowsMidiCommunicator.java:79)
at WindowsMidiCommunicator.<init>(WindowsMidiCommunicator.java:28)
at WindowsMidiCommunicator.getInstance(WindowsMidiCommunicator.java:32)
at SafferOrganizedTest$1.run(SafferOrganizedTest.java:28)
at java.util.TimerThread.mainLoop(Unknown Source)
at java.util.TimerThread.run(Unknown Source)
答案 0 :(得分：0)
目前尚不清楚您的实际问题是什么，因为您尚未发布错误消息。但是，单例实现并不是惯用的或正确的，主要是因为类的构造函数是protected。这意味着任何对类进行子类化的人都可以创建它的其他实例 - 使类不再是单例。
在Java 5及更高版本中实现单例的最简单方法是使用具有单个值的枚举：
public enum Communicator {
INSTANCE;
private Connection conn;
Communicator() {
// set up the Connection here
}
/* public methods */
public void doSomething() {
//...
}
}
这样，您只需使用Communicator.INSTANCE.doSomething()调用您的单身人士。