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Method return values and/or error codes must accurately specify the object's state at an appropriate level of abstraction. Clients must be able to rely on the value for performing critical decisions.

Noncompliant Code Example

As shown in this noncompliant code example,the updateNode() method modifies a node if it can find it in a linked list and does nothing if the node is not in the list. 

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This method fails to indicate whether it modified any node. Such methods are prone to misuse; as such a method is likely to modify data in an unexpected fashion.

Compliant Solution (boolean)

This compliant solution returns the result of the operation as true if it modified a node and false if it did not.

public boolean updateNode(int id, int newValue) {		
  Node current = root;
  while (current != null) {
    if (current.getId() == id) {
      current.setValue(newValue);
      return true; // Node successfully updated
    }
    current = current.next;
  }
  return false;
}

Compliant Solution (exception)

This compliant solution returns the modified Node when one is found and throws a NodeNotFoundException when the node is not available in the list.

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Using exceptions to indicate failure can be a good design choice, but throwing exceptions is not always appropriate. In general, a method should throw an exception when it is expected to succeed but an unrecoverable situation occurs or when it expects a method higher up in the call hierarchy to initiate recovery.

Compliant Solution (null return value)

This compliant solution returns the updated Node so that the developer can simply check for a null value if the operation fails. 

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A return value that might be null is an in-band error indicator, which is discussed more thoroughly in 4.0352. Avoid in-band error indicators. This design is permitted but is considered inferior to other designs, such as those shown in the other compliant solutions in this guideline.

Applicability

Failure to provide appropriate feedback through a combination of return values, error codes, and exceptions can lead to inconsistent object state and unexpected program behavior.

Bibliography

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