ConstructiCat Logo
CodeBust.
Browse section ▾

Replace Error Code with Exception.

Problem

A method returns a special value that indicates an error?

Solution

Throw an exception instead.

##Example

Before
int withdraw(int amount) {
  if (amount > _balance) {
    return -1;
  }
  else {
    balance -= amount;
    return 0;
  }
}
After
void withdraw(int amount) throws BalanceException {
  if (amount > _balance) {
    throw new BalanceException();
  }
  balance -= amount;
}

##Why Refactor

Returning error codes is an obsolete holdover from procedural programming. In modern programming, error handling is performed by special classes, which are named exceptions. If a problem occurs, you “throw” an error, which is then “caught” by one of the exception handlers. Special error-handling code, which is ignored in normal conditions, is activated to respond.

##Benefits

  • Frees code from a large number of conditionals for checking various error codes. Exception handlers are a much more succinct way to differentiate normal execution paths from abnormal ones.

  • Exception classes can implement their own methods, thus containing part of the error handling functionality (such as for sending error messages).

  • Unlike exceptions, error codes can’t be used in a constructor, since a constructor must return only a new object.

##How to Refactor

Try to perform these refactoring steps for only one error code at a time. This will make it easier to keep all the important information in your head and avoid errors.

  1. Find all calls to a method that returns error codes and, instead of checking for an error code, wrap it in try/catch blocks.

  2. Inside the method, instead of returning an error code, throw an exception.

  3. Change the method signature so that it contains information about the exception being thrown (@throws section).

← Previous
Replace Constructor with Factory Method
Next →
Replace Exception with Test