Question

I am currently studying for the SCJP certification using the Sierra and Bates Study Guide and in many of the self tests (mock exam questions) I keep running into the same problem – I can’t tell whether a particular error will be at runtime (an exception) or at compile (compile error). I know this is a bit of a vague question and that it might not be possible to answer but, how can I tell if an error will be found at compile or at runtime? Would you be able to send me some website links that might be able to help me?

Answer 1

Compile time error – the java compiler can’t compile the code, often because of syntax errors. Typical candidates:

• missing brackets
• missing semicolons
• access to private fields in other classes
• missing classes on the classpath (at compile time)

Runtime error – the code did compile, can be executed but crashes at some point, like you have a division by zero.

• using variable that are actually null (may cause NullPointerException)
• using illegal indexes on arrays
• accessing resources that are currently unavailable (missing files, …)
• missing classes on the classpath (at runtime)

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(‘Crashes’ is really not the correct term and is only used to illustrate what happens)