Week 2: Classes, interfaces and variable length parameters

Week 2: Classes, interfaces and variable length parameters

1. Access modifiers

   • private
     • accessible wihin class only
   • proteced
     • accessible in package and sub-classes
       • sub-class might not be same package
       • same package should not access but may
   • public
     • accessible anywhere
     • inteface public by default

2. Other modifiers (non-access)

   • static
     • may access field/method via class
     • does not require object instance
     • fields/methods shared by all instance of class
     • static inner class may be intantiated without outer class
   • final
     • may not be changed once initiaised
       • class cannot subclasses thus extended
       • field initialise once and cannot be changed
       • method can't be overidden

3. Types of classes

   • Named/'normal'
     • instantiated
     • multiple instances
     • has fields
     • all methods implemented
     • can be extended/implemented
   • Abstract
     • cannot instantiate
     • used as base class for inheritance (used for polymorphism)
     • multiple instances
     • methods abstract or implemented
     • can be extended or implemented
     • large group, related data
   • Inner
     • may access outer class field & methods
     • cannot exist alone (unless static)
       • instantiated within outer class
     • multiple instances
     • all methods implemented
     • can be extended or implemented
     • only makes sense or is valid in the outer class
       • not reusable in another context
   • static inner
     • same as named class
     • use when wanting a nested relationship but still accessible outside
   • Anonymous
     • defined inline
       • no name
     • class declared and instantiated at same time
     • cannot have multiple instances
     • cannot be extended or implemented
     • use: small object to implement. extension not important