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7.Testability of Classes and Methods (Method Chaining (Handling …

- - - - Instance variables (which make them have constant value)
      - On classes (which make them unable to have subclasses)
      - On methods (which make them not able to be overriden by subclasses)
      - On Method parameters (which makes the arguments immutable)
- - - - In our class A, lets say we need
        method moveTo() from class B.
        What we can do is to create an
        overriding method moveTo() in bStub,
        which returns a hardcoded result
        that moveTo() should return.
        If handling multiple test cases,
        use switch-case (refer to Lecture Slides)
- - - - To handle this, we create a static factory method, and make actual constructor private.
        class Circle {
        private final Point centre;
        private final double radius;
        private Circle(final Point centre, final double radius){
        this.centre = centre;
        this.radius = radius;
        }
        public static Circle createCircle(final Point centre, final double radius) {
        if (radius < 0.0)
        return null;
        else
        return new Circle(centre, radius)
  - - - need to import java.util.Optional
        
        make use of orElse methods & .empty() etc. Read Optional Class API
        
        When .empty() is invoked, it returns Optional.empty which basically means null, but since its an Object, we can chain this, without getting NullPointerExceptions. So at every method, we should check if we are dealing with OptionalEmpty, by checking isPresent(). If Optional.empty, handle exception