RuntimeExceptions.md

RuntimeExceptions

Contents

• Why
• 1. Throw as error (Exception)
  • A. Unnecessary Wrapping
  • B. Returning Exceptions
• 2. Throw as error (Action/Function)
• 3. Wrapping Actions/Functions

Why

It is our belief that checked exceptions were a mistake in the Java language. Fortunately, Java provides two methods for unchecked exceptions: RuntimeException and Error. Checked exceptions will also show up in the signatures of methods, creating troubles with lambdas

Approval Utilities provides the following techniques for converting checked exceptions into unchecked exceptions.

1. Throw as error (Exception)

The most basic method to do this is to wrap a checked exception in a runtime exception. Here is an example of this:

try
{
  methodThatMightThrowCheckedException();
  methodThatMightThrowRuntimeException();
  methodThatMightThrowError();
}
catch (Throwable t)
{
  throw ObjectUtils.throwAsError(t);
}

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There are two things to note in this implementation.

A. Unnecessary Wrapping

ObjectUtils.throwAsError will not wrap Error or RuntimeException as they are already unchecked.

B. Returning Exceptions

ObjectUtils.throwAsError pretends that it will return an Error. The reason it does this is so that the calling code can pretend to throw it. In practice, throwAsError() will always throw the Error. So whether or not you specify a throw at the calling code is irrelevant to the execution, but can be helpful for compilation of the calling code.

2. Throw as error (Action/Function)

If you want to run a small piece of code without the overhead of the try/catch block, you can accomplish this through the use of lambdas. Here are examples with and without return values:

ObjectUtils.throwAsError(() -> methodThatMightThrowCheckedException());
int i = ObjectUtils.throwAsError(() -> methodThatMightThrowCheckedExceptionWithReturnValue());

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3. Wrapping Actions/Functions

If the issue is in the signature of the lambda you will need to convert from a lambda whose signature allows checked exceptions to one that doesn't. To do this you will use either Actions.unchecked() / Functions.unchecked()

Here's an example which allows us to wrap a lambda that throws an IOException:

Queryable<String> paths = files.select(Functions.unchecked(
    // throws IOException
    s -> new File(s).getCanonicalPath()));

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