What are some potential trips/traps in the SCJP exam?

• Two top-level public classes cannot be in the same source file.
• main() cannot call an instance (non-static) method.
• Methods can have the same name as the constructor(s).
• Watch for thread initiation with classes that don't have a run() method.
• Local classes cannot access non-final variables.
• Case statements must have values within permissible range.
• Watch for Math class being an option for immutable classes.
• instanceOf is not the same as instanceof.
• Constructors can be private.
• Assignment statements can be mistaken for a comparison; e.g., if(a=true)...
• Watch for System.exit() in try-catch-finally blocks.
• Watch for uninitialized variable references with no path of proper initialization.
• Order of try-catch-finally blocks matters.
• main() can be declared final.
• -0.0 == 0.0 is true.
• A class without abstract methods can still be declared abstract.
• Map does not implement Collection.
• Dictionary is a class, not an interface.
• Collection (singular) is an Interface, but Collections (plural) is a helper class.
• Class declarations can come in any order (e.g., derived first, base next, etc.).
• Forward references to variables gives a compiler error.
• Multi-dimensional arrays can be "sparse" -- i.e., if you imagine the array as a matrix, every row need not have the same number of columns.
• Arrays, whether local or class-level, are always initialized
• Strings are initialized to null, not empty string.
• An empty string is not the same as a null reference.
• A declaration cannot be labelled.
• continue must be in a loop (e.g., for, do, while). It cannot appear in case constructs.
• Primitive array types can never be assigned to each other, even though the primitives themselves can be assigned. For example, ArrayofLongPrimitives = ArrayofIntegerPrimitives gives compiler error even though longvar = intvar is perfectly valid.
• A constructor can throw any exception.
• Initializer blocks are executed in the order of declaration.
• Instance initializers are executed only if an object is constructed.
• All comparisons involving NaN and a non-NaN always result in false.
• Default type of a numeric literal with a decimal point is double.
• int and long operations / and % can throw an ArithmeticException, while float and double / and % never will (even in case of division by zero).
• == gives compiler error if the operands are cast-incompatible.
• You can never cast objects of sibling classes (sharing the same parent).
• equals() returns false if the object types are different. It does not raise a compiler error.
• No inner class (non-static inner class) can have a static member.
• File class has no methods to deal with the contents of the file.
• InputStream and OutputStream are abstract classes.