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javaexceptioncompilationscjp

Java - When is it a compiler error and when is it a runtime exception?

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?

Solution

  • 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)

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