OCM Concepts

Introduction

OCM Concepts, otherwise known as Objects, Classes and Methods are constructs in Object Oriented programming languages.

We will be taking a look at how Objects, Classes and Constructors work in Java.

Objects

An Object is a basic unit of OO Programming and represents the real life entities. A typical Java program creates many objects, which as you know, interact by invoking methods. An object consists of:

State - It is represented by attributes of an object. It also reflects the properties of an object.
Behaviour - It is represented by methods of an object. It also reflects the response of an object with other objects.
Identity - It gives a unique name to an object and enables one object to interact with other objects.

For Example: A Cat, the name of this Cat is Cleo. The attributes of the Cat are its breed (Tabby), age (5), color (brown). And its behaviours, meow, sleep, eat, purr.

Objects correspond to things found in the real world. For Example, a graphics program may have objects such as "circle", "square", "menu". An online shopping system might have objects such as "shopping cart","customer", and "product".

                        
                            public class Cat{

    String breed;
    int age;
    String color;

    void meowing(){

    }

    void hungry(){

    }

    void sleeping(){

    }

}

The member variable marks has bee marked as private. That means, that the member variable time inside the Exam class cannot be accessed from code outside the Exam class.

Classes

A class is a user defined blueprint or prototype from which objects are created. It represents the set of properties or methods that are common to all objects of one type. In general, class declaratios can include these componenets, in order:

Modifiers: A class can be public or has default access
Class name: The name should begin with a initial letter (capitalized by convention)
Superclass(if any): The name of the class's parent (superclass), if any, preceded by the keyword extends. A class can only extend (subclass)one parent.
Interfaces(if any): A comma-separated list of interfaces implemented by the class, if any, preceded by the keyword implements. A class can implement more than one interface.
Body: The class body surrounded by braces, {}

Constructors are used for initializing new objects. Fields are variables that provides the state of the class and its object, and methods are used to implement the behaviour of the class and its objects.

There are different types of classes that are used in real time applications such as nested classes, anonymous classes, lambda expressions.


                                Cat Cleo = new Cat();

Above is a way how to declare an object in Java.

Methods

A method is a collection of statements that perform some specific task and return the result to the caller. A method can perform some specific task without returning anything. Methods allow us to resuse the code without retyping the code. In Java, every method must be part of some class which is different from languages like C, C++, and Python.

Methods are time savers and help us to reuse the code without retyping the code.

There are 6 components in a method declaration. We will go through this in another article. But below is the syntax of declaring a method:

                        
                            public int addNums(int x, int y){

    return (x+y);

}

//call it here

addNums(6,5);

// result will be 11

Conclusion

There are many ways to use classes, methods and objects. These include:

Declarations
Initializing
Creating
Annoymous Objects
Method Declaration Components
Constructors

These will all be mentioned in a future chapter.

Sources: (click on them to see them)

Objects, Classes and Methods Concepts