try/catch Flow - Week 3 Visual

A runtime error normally crashes your program. A try/catch block lets you intercept the problem and keep running.

You broke the rules of the Java language. Missing semicolon, typo in a keyword, unclosed brace.

Caught by: the compiler, before the program runs. You can't even launch it.

The code runs fine — it just produces the wrong answer. Java has no idea anything is wrong; it's doing exactly what you told it to do.

Caught by: you, reading the output. This is where the debugger helps.

The program started fine but then hit something unexpected — bad input, a missing file, an out-of-range index. Java throws an exception.

Caught by: a try/catch block. Without one, the program crashes.

How try/catch routes execution

try { … }

Code runs here.
Everything works → finish normally.
Something breaks → throw an exception.

⤵

exception
thrown

catch (Exception e) { … }

Control jumps here.
You decide what to do — log it, show a friendly message, ask again.
Then execution continues past the catch.

Without try/catch: the exception keeps bubbling up until Java has nowhere else to go — the program halts and prints a stack trace.

With try/catch: you intercept the problem at the try block's boundary. Program keeps running.

Tip: press a quick-pick button to set the number, then Run. Switch modes to see the same input produce two very different outcomes.