Instance Variables

API ID: CountDeclInstanceVariable
Also Known As: Number of Instance Variables (NIV)
Languages: Basic, C#, C++, Java, Pascal, Python, Web
Targets: Architectures, Classes, Files, Project

Number of instance variables.

Variables defined in a class that are only accessible through an object of that class.

For example:

class BoatCar: private Car, public Boat, protected DualPurpose {
public:
  // Public Instance Function
  BoatCar() : Car(4), Boat(), mInWater(false), mColor("Blue") {}
  virtual int passengers() const { return 4; }

  static int numRegistered() { return sRegistered; }

  bool mInWater; // Public Instance Variable

protected:

  void toggleInWater(bool inWater) { mInWater = inWater; }
  char * mColor; // Protected Instance Variable
  friend void init() {}

  static int sRegistered;
  static double calcSpeed(double distance, double time) {
    return distance/time;
  }

private:
  int mMaxPassengers;
  void travel() {}
};

BoatCar declares three instance variables across all access levels — mInWater (public), mColor (protected), and mMaxPassengers (private) — so CountDeclInstanceVariable = 3.

See Public Instance Variables, Protected Instance Variables, and Private Instance Variables for the breakdown by access level, and Class Variables for the static counterpart. C# also has additional access levels: see Internal Instance Variables and Protected Internal Instance Variables.

Also known as Lorenz & Kidd - Number of Instance Variables (NIV).

Targets By Language:

• Basic: Project, Class, Struct
• C#: Project, Class, Struct
• C++: Project, Class, Struct, Union
• Java: Project, File, Class, Interface
• Pascal: Project, Class, Interface
• Python: Project, Class
• Web: Project, PHP Class, PHP Interface

Configuration:

• For projects and architectures, this metric must also be enabled from "Project Configuration/Metrics/Projects and Architectures" with the "Show aggregated class metrics" option. Enabling this option can be time consuming.
• This metric can be disabled from "Project Configuration/Metrics/Object Orientated" with the "Show method and variable count metrics" option.