Fix findbugs violations in openflowjava

Fix findbugs violations in openflowjava

- Invocation of toString on an array

- Check for sign of bitwise operation:
Example: ((event.detail & SWT.SELECTED) > 0)

Using bit arithmetic and then comparing with the greater than operator
can lead to unexpected results (of course depending on the value of
SWT.SELECTED). If SWT.SELECTED is a negative number, this is a candidate
for a bug. Even when SWT.SELECTED is not negative, it seems good practice
to use '!= 0' instead of '> 0'

- Reliance on default encoding - performs a byte to String (or String to byte)
conversion, and will assume that the default platform encoding is suitable.

- Primitive value is boxed then unboxed to perform primitive coercion

- Unread field

- Result of integer multiplication cast to long - possible overflow

- Dead store to local variable - assigns a value to a local variable, but
the value is not read or used in any subsequent instruction.

- Method uses the same code for two switch clauses

- Load of known null value

- Consider returning a zero length array rather than null

- Redundant nullcheck of value known to be non-null

- Field not initialized in constructor but dereferenced without null check

- Non-transient non-serializable instance field in serializable class

- Class implements same interface as superclass

Change-Id: I28b533c9f9805de539e35b729c5163fd22e75354
Signed-off-by: Tom Pantelis <tompantelis@gmail.com>