Intermediate 25 min read

Try, Catch, and Finally

By the end of this lesson, you'll be able to:

Write a try/catch block to handle a runtime exception without crashing
Explain what code inside finally guarantees
Recognize the difference between an exception being thrown and being handled

Prerequisites: "ApexDoc and Documentation Standards"

Catching an exception

Decimal result;

try {
    result = 10 / 0;
} catch (MathException e) {
    System.debug('Caught a math error: ' + e.getMessage());
    result = 0;
}

System.debug('Continuing normally: ' + result);

Without try/catch, 10 / 0 would throw a MathException and immediately stop the whole transaction (as seen back in Module 8). Wrapping it in try lets catch step in, handle the problem, and let execution continue normally afterward — 'Continuing normally' still prints.

finally always runs

try {
    Decimal result = 10 / 0;
} catch (MathException e) {
    System.debug('Handled: ' + e.getMessage());
} finally {
    System.debug('This always runs, error or not.');
}

The finally block runs whether the try succeeded, failed and got caught, or even failed in a way nothing caught — it's the right place for cleanup that must always happen regardless of outcome, like closing a resource or logging that an operation finished.

A real business example: Order Processing

public String processOrder(Decimal orderTotal, Decimal discountPercent) {
    try {
        Decimal discount = orderTotal * (discountPercent / 100);
        return 'Order total after discount: ' + (orderTotal - discount);
    } catch (Exception e) {
        System.debug('Failed to process order: ' + e.getMessage());
        return 'Order could not be processed.';
    } finally {
        System.debug('Order processing attempt finished at ' + System.now());
    }
}

An order-processing method that might fail for any number of reasons returns a sensible fallback message instead of crashing — while finally logs that the attempt happened, successful or not, useful for auditing.

Exercise

Write a try/catch that attempts Decimal result = 20 / 0, catches MathException, debugs "Division failed", and uses finally to debug "Attempt complete".

Show hint

try { ... } catch (MathException e) { ... } finally { ... }

APEX

Try, Catch, and Finally Quiz

1. When does code inside a finally block run?

Always, whether the try block succeeded or an exception was thrown and caught Only if an exception occurs Only if no exception occurs Never, unless explicitly called

My Notes

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Summary

try/catch lets code recover from a runtime error instead of crashing the whole transaction; finally guarantees a block of cleanup code runs no matter what happened in the try.

← ApexDoc and Documentation Standards Common Built-In Exceptions →