Objects & Classes

Objects & Classes

1. Objects/Instance (Car)

   • Attributes/Fields
     • Color, Number of Tires, Plate Number
   • Actions/Methods
     • Run, Brake
   • Constructing Object/Instantiating Class- use new!
     • assign created object to object/reference variable
       • Type/Constructor objectReference = new Constructor();
       • if the reference variable does not have a value, assign null
         • test if reference variable is null using == ex.  if (book==null) {      book=new Book(); } System.out.println(book.title);
     • call an object/field using .
       • objectReference.methodName objectReference.fieldName

2. Classes are blueprints to create objects

3. Classes

   • class className{      [class body] }
   • Class Name
     • Capitalize the initial of each word (Pascal), same as constructor name!
       • Saving file: ClassName.java
   • Fields (Variables)
     • Capitalize initial of each word except the first (Camel) (Same for Methods)
     • Primitive or references to objects (other classes)
   • Methods
     • Declaration/Signature
       • return value, method name, list of arguments
         • syntax: returnType methodName (listOfArguments)
         • return type can be primative, an object, or void (return nothing)
     • Body
       • code to perform action
     • Main- method providing entry point to application (how to invoke a specific class)
       • signature: public static void main(String[] args)
       • Passing Arguments
         • java className arg1 arg2 arg3
           • arguments must be strings
   • Constructors
     • constructorName(listOfArguments){      [constructor body] }
     • used to construct an object, sometimes called a constructor method, no return value
     • constructor arguments are used to initialize fields in the object