Question

Let’s say I have the following Java interface that I may not modify:

public interface MyInterface {
  public void doSomething();
}

And now the class implementing it is like this:

class MyImplementation implements MyInterface {
  public void doSomething() {
    try {
      // read file
    } catch (IOException e) {
      // what to do?
    }
  }
}

I can’t recover from not reading the file.

A subclass of RuntimeException can clearly help me, but I’m not sure if it’s the right thing to do: the problem is that that exception would then not be documented in the class and a user of the class would possibly get that exception an know nothing about solving this.

What can I do?

---

We all agree: the interface is faulty.

Solution I chose

I finally decided to write a MyVeryOwnInterface that extends MyInterface and adds as part of the signature of the faulty methods the MyRuntimeException:

public interface MyVeryOwnInterface extends MyInterface {
  public void doSomething() throws MyRuntimeException;
}
class MyImplementation implements MyVeryOwnInterface {
  public void doSomething() throws MyRuntimeException {
    try {
      // read file
    } catch (IOException e) {
      throw new MyRuntimeException("Could not read the file", e);
    }
  }
}

Answer 1

You’ve encountered the problem of leaky abstractions. There is no really good solution, and using a RuntimeException pretty much the only thing you can do.

Arguably, this is also an example for why checked exceptions are a failed concept.