Learn · OOP & Java

Exceptions & Error Handling

Things go wrong — a file’s missing, the network drops, a number won’t parse. Exceptions let your program deal with it instead of just dying.

The idea — a safety net

An exception is the program saying “something went wrong here” and jumping to your plan B instead of crashing. You wrap risky code in try, handle the problem in catch, and clean up in finally.

try {
    int x = Integer.parseInt(input);   // might fail
} catch (NumberFormatException e) {
    // plan B: tell the user it wasn't a number
} finally {
    // always runs — close files, release locks
}

Checked vs unchecked

Handle errors well

• Catch specific, not a blanket catch (Exception e) that hides real bugs.
• Never swallow — an empty catch block hides failures until they explode later.
• Clean up in finally (or try-with-resources) so files/connections always close.
• Fail with a clear message — “order 123 not found”, not a raw stack trace to the user.

Where you’ll use it — real life

Next: Generics →