Exceptions communicate failure to a boundary that can decide recovery. Preserve causes and distinguish expected domain outcomes from unexpected failures.
Before you start
You should know Java classes, methods, collections and exceptions. Trace object identity separately from the contents of an object. For concurrent examples, state which thread owns or shares the data; a single successful execution is not proof that every interleaving is safe.
The practical goal is to reason through this situation: Wrap a low-level exception with operation context while retaining its cause. Read the walkthrough first, then try the interview exercise before opening its answer. The important part is explaining the decision and its consequences, rather than remembering a definition alone.
Step-by-step walkthrough
Step 1: Identify a recovery boundary
The layer choosing a response needs operation context and the cause.
Step 2: Preserve failure information
Wrap with a cause instead of returning null for every exception.
Step 3: Classify safe recovery
Retry only failures and operations whose side effects are understood.
Worked scenario
Wrap a low-level exception with operation context while retaining its cause.
A repository read failing is not the same as a successful read returning no record. Returning null for both prevents callers from distinguishing service outage from not-found. Preserve the underlying cause internally and map only documented failures to controlled public outcomes.
Common mistake
Catching Exception and silently returning null hides both failure and absence.
Verify the behavior
Test missing records, dependency failure and unexpected bugs as distinct outcomes.
Interview exercise
Handle an unavailable dependency.
Answer and reasoning
Map known failures to a documented outcome, log safe diagnostics and avoid retrying operations without understanding their side effects.
Continue learning
Compare the scenario with the Java interview questions and test your understanding with the Java MCQs. For terminology and implementation details, consult the reference material.