Try and Catch Basics

Some things can fail and you do not know ahead of time. A user types a number into a form, a query finds no records, a call to an outside service times out. The code still has to keep running, so Apex gives you a way to say: try this, and if it goes wrong, do this other thing instead.

The try Block

A try block holds the code that might fail. The moment anything inside it throws, Apex stops running the rest of the block and looks for a matching catch:

try {
    Integer value = Integer.valueOf(userInput);
    System.debug(value);
} catch (Exception e) {
    System.debug('That was not a number');
}

If userInput holds 42, the debug prints 42 and the catch never runs. If it holds hello, Integer.valueOf throws, the debug line is skipped, and the catch runs.

Catching a Specific Type

Exception is the parent of every error type Apex knows about, so catch (Exception e) catches everything. You can also catch a more specific type when you only want to handle one case. Integer.valueOf throws a TypeException when the text is not a valid number, so catching that one type is enough to make the code safe:

try {
    return Integer.valueOf(input);
} catch (TypeException e) {
    return 0;
}

Why This Matters

Code that does not handle failure leaves the user with a confusing error page. A well-placed try and catch lets the rest of the program keep going with a sensible default, and the user sees a clear result instead of a crash.