Objects and Classes in Java

Objects and Classes in Java

1. Java Object

   • Definition: A model that represents a real situation used to solve the main problem. An object consists of attributes (fields) and actions (methods/functions)
     • Fields
       • Fields define certain characteristics of the object. They are variables that can be primitives or even references to another object.
       • Fields follow the camel naming convention: age, maxAge, name, lastName, etc.
     • Methods
       • Methods define the actions the object can take. It consists of a a declaration and a body. The declaration has a return value, the method name, and a list of arguments. The body contains the code that performs the action.
         • returnType methodName (listOfArguments)
           • The return type can be a primitive, object, or void. Void means the method returns nothing
       • The Method Main
         • The method main acts as the entry point to an application. It allows the class containing it to be invoked.

2. Java Class

   • Definition: A class serves as the template used to create an instance of an objects of identical type. The three main things a class should contain is the class name, the object's fields, and the object's methods.
     • class className { [class body] }
     • Class names follow the Pascal naming convention: Boss, PostOffice, StudentGrades, etc.
     • A class definition must be saved in a file that has the same name with the java extension. For example: Employee.java for the employee class.
     • A UML diagram is a useful way to conceptualize a class. It is a rectangle separated into three parts: the class name, the list of fields, and the list of methods.
     • Constructors
       • A constructor is used to construct an object. Every class must have at least one constructor or else the class is useless. Their syntax is similar to that of a method but has no return value.
       • A constructor with zero argument is called a no argument constructor. Constructor arguments can be used to intialize the fields in an object
       • constructorName (listOfArguments) { [constructor body] }