Types: Primitive Types & Classes

Primitive types

• int, float, and double are basic primitive types. There are other primitive types also: boolean, char, etc.
• We can have many values of any of these types.
• To construct a primitive type value, just declare a variable of that type and initialize it.
• There is a set of operators defined to work with each primitive type (e.g., the arithmetic operators: +, -, *, /, etc.)
• Examples:

      int radius = 2;
      int diameter = radius * 2;
      double pi = 3.14159;
      double area = pi * radius * radius;
  

• Naming convention: variable names start with lower-case letters. The primitive type names are also lower-case, and must by spelled exactly as defined.

Classes

• A class defines a new type. We can have many values of that type, called objects or instances of the class.
• The operations on a class type are its methods or functions.

  Clock	Fish	Greeter
  getHour() getMinute()	moveForward() turnAround() swimUp()	sayHello()

  To find out what methods are available for a class, look at its class documentation.
• The syntax for calling or invoking a method is:

      object.methodName()    e.g., myClock.getHour()
  

  Methods always include parentheses. If the method needs the user to pass some information to it, that information goes inside the parentheses.
• Classes have special methods called constructors. The name of a constructor is always the same as the name of the class. You construct an object with the new keyword and the constructor.
• Examples:

      Fish fish1 = new Fish();
      fish1.moveForward();
      fish1.swimUp();
  

• Naming convention: class names start with upper-case letters, while object variable names and method names start with lower-case letters.