⚠️ This lecture introduces exceptions — Java's mechanism for handling abnormal situations without breaking the type system. It covers the motivation (why if statements and error codes aren't enough), throwing and declaring exceptions, the try-catch block, exception propagation through the call stack, multiple catch clauses, checked vs unchecked exceptions, and the finally block.
At-a-glance Checklist
- [ ] Explain why using
if statements and error codes to handle errors is messy and limited
- [ ] Understand the return type problem — a boolean method has no spare value to signal an error
- [ ] Know that exceptions provide an extra communication channel separate from the return value
- [ ] Write code that throws an exception with
throw new ExceptionType(...)
- [ ] Declare exceptions in a method header with
throws ExceptionType
- [ ] Understand exception propagation — if uncaught, exceptions travel back up the call stack
- [ ] Write a try-catch block to handle an exception
- [ ] Know that try and catch are mutually exclusive — only one path executes
- [ ] Handle multiple exception types with multiple catch clauses
- [ ] Understand catch clause ordering — more specific exceptions must come first
- [ ] Distinguish checked exceptions (must declare) from unchecked exceptions (don't have to declare)
- [ ] Name common unchecked exceptions:
ArithmeticException, ArrayIndexOutOfBoundsException
- [ ] Know that a method catching all its exceptions does not need
throws in its header
- [ ] Understand the purpose of the
finally block
The Problem: Why Do We Need Exceptions?
Error Handling Without Exceptions
Imagine you're working with a file — opening, reading, writing. Lots of things can go wrong: