The Big List of Problems

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Using a compiler and programming environment for the first time is frustrating and tricky. Let's collect a bunch of the important problems and their causes, so that you can scan the list rather than getting stuck. Tell me when you have a new one to add!

DrJava

DrJava won't let me edit the files.
The files are not editable: you need to make an editable copy of them elsewhere.
DrJava doesn't show the changes I made when I run my program.
Chances are that there are compilation errors: fix all the errors before you look at what the program does.
DrJava is still running my old program, not the new one, and it compiles fine.
You may have to set the project to look in another class for the main().
DrJava can't find my class or image or other file.
You may not have a project or you may have to set the project to look in the correct folder.

Compiler

Compiler messages are notoriously cryptic. The causes of the commonest compiler complaints are from:

  • Forgetting a semicolon.
  • You haven't declared a field.
  • Capitalization differences.
  • Calling a method with the wrong types or numbers of arguments.
  • Non-matching "double" or 'single' quotes, (parentheses), or {braces}
  • Trying to use a method from another class.
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