What are the pitfalls of a Java noob? [closed]

Answer 1

Some mistakes I have seen people make who are experienced at programming but not at Java:

1. Classes implicitly extend Object
2. Classes implicitly import java.lang.*
3. instanceof doesn't require a not null check
4. Upcasting, e.g. ((Object)new Integer(1)).toString(), is almost never useful as it doesn't affect dynamic method selection
5. Strings are immutable. There is no need to copy or clone them.
6. Don't rely on the garbage collector or finalize() to perform resource (rather than memory) management. Resources, e.g. files, should be closed explicitly.
7. Swing components, once displayed, should only be accessed from the AWT event thread (typically using SwingUtilities.invokeLater()).
8. In general, be very, very careful when multiple threads share the same mutable/stateful objects. Either copy your objects first, or be prepared to use a while lot of synchronized blocks, wait() and notify().