Question

I am writing a custom queue implementing the queue interface. This implementation is thread safe and blocks on certain occasions.

The normal Queue interface does not mention Exceptions, therefore I can’t throw any InterruptedException in my implementation.

I see two solutions for this problem, but they are both not very satisfying:

1. Remove the Queue interface and throw Exceptions. This makes the code unusable for foreign software that requires a Queue.

2. Throw RuntimeException, this will yield tonnes of very surprising software activity, which I don’t want to risk.

Somehow implementations like ArrayBlockingQueue manage to implement Queue and BlockingQueue. Is that the way to go, or what is the trick here?

Answer 1

If you are implementing a Queue which may need to throw an InterruptedException then my guess is that you really want to implement a BlockingQueue. If you read the javadoc for this interface, you will realize that the Java language designers have basically said that in the context of a BlockingQueue the normal Queue operations will either succeed or fail immediately. The Queue interface provides for throwing an IllegalStateException if the add method can not succeed or returning false if the offer method fails. New methods put and take as well as an overloaded variant of offer and poll are introduced by the BlockingQueue interface for operations that may block and therefor need to throw an InterruptedException.