try/catch

If you know that some code might fail, and you have an idea of what to do if it does, you can prevent an exception from crashing your program by catch-ing it.

To do this, you write try and put the code that might fail inside of { and }.

try {
    mightFail();
}

Then you write catch and in parentheses the kind of exception you want to handle as well as a variable name.¹

try {
    mightFail();
} catch (RuntimeException e) {

}

And inside the catch block you can write code to run when such an exception occurs.

void doThing(int x) {
    if (x == 0) {
        throw new RuntimeException("Cannot do something zero times");
    }
}

void main() {
    int x = 0;
    try {
        doThing(x);
    } catch (RuntimeException e) {
        System.out.println("Something went wrong doing a thing.");
    }
}

Just as you cannot have an else without an if, you cannot have a catch without a try.

void main() {
    catch (RuntimeException e) {
        System.out.println("Hello");
    }
}

Nor can you have a try without a catch.²

void main() {
    try {
        System.out.println("Hello");
    }
}