fix PROP_XXX constants, apply some refactorings

[xzel23]

• fix invalid bitwise operations: 1 << (32+i) is the same as 1<< i, the shifted value needs to be long for this to work
• encapsulate "type" - it was mutable and public
• assign fieldMap directly, make it a static final constant and change the name accordingly; add getFieldMap() method for access