Stage 1 · Lesson 8 of 9
Exceptions and stack traces
Java signals errors with . The , read from the top, gives the exception type, the message and the exact line. There are two kinds.
exceptions, such as IOException, are failures you should plan for, like a missing file. The compiler makes you either catch them or declare them with throws in the . Unchecked exceptions, such as NullPointerException or ArrayIndexOutOfBoundsException, usually mean a bug to fix rather than catch.
Use try, catch and finally for expected failures. Use , try (var reader = ...), to close files automatically when you are done. Catch the narrowest type you can, never leave a catch block empty, and throw IllegalArgumentException for bad input.
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Resources for this stage
Start with· follow one of these
- CourseFreeJava Programming MOOC
University of Helsinki · Beginner
Free Helsinki course with hundreds of auto-tested exercises; parts 1 to 8 cover this stage
- GuideFreeDev.java: Learn Java
Oracle · Beginner
Official tutorials from the Java team: read the language basics path next to the MOOC