Class and object are the two most important concepts in programming especially when dealing with Object-Oriented Programming (OOP) Languages like Java. These two concepts allow the programmer to build their code using real life models and their functions thus ensuring that the software projects are organized and focused.

In order to learn how Java operates as an object oriented language, it is necessary to first consider what are classes and objects and what are their roles in the Java language. Through this article, we shall address these questions and provide clear definitions of the basic concepts such as class and objects and their interrelationships, how these concepts interrelate and contribute to the orderly construction of Java programs.

1. What is a Class?

The basic building block of Java is the class whose meaning is often reduced to a structural or design template used for object construction. In many ways a class is similar to an outline; it explains the components and processes involved but is not itself an end product. The class describes what attributes and behaviors the objects built from that class will hold.

Two major elements are covered in a class:

- Attributes (Fields) : These are essential characteristics and qualities that are used to describe an object. They depict the data that the object is expected to own.

- Methods : These are the various actions that the object is enabled to perform. Methods describe the logic or the functionality of an object.

In simple terms, a class describes the theory, while objects are tangible or real-life instances of the theory in question. For instance, class might mention cars in general while its object would be some particular car, let's say, red sedan.

1.1 Characteristics of a Class

In Java, there are a few fundamental properties of a class that specify its functionality:

- Constructor : Any class has the option of defining a special function which is referred to as a constructor. This function serves to create new instances of the class. It is executed when an instance is created so that the instance variables take on their initial values as defined in the constructor.

- Access Modifiers : To guarantee preservation of object information, the Java programming language supports the use of keywords which control various levels of visibility and usage of the class and class members (attributes and methods) and these keywords are termed as access modifiers. This sorts out the various levels of access that would be accorded to objects and their associated data.

- Static and Non-Static Members : It should be noted that Java classes could be composed of both static and non-static members. Static members are those that are defined at the class level and they are universal to all the instances of the class while non-static members are specific to each and every instance that has been defined for the class.

2. What do you mean by Object?

An object is referred to as an instance of a class. In Java, an object is a class defined physical asset, built using the class definition. Even though a class defines the characteristics of the object that it is meant to be, the object is the class of entity that a user deals with the program for.

So when you declare a variable as an object type in Java, what you are doing is declaring that this variable will have some state and also a behavior that will be provided by its respective class. With that said, all objects contain:

- State : the state of an object, according to their properties or characteristics, maintains the values contained in their attributes. Specifically, a Car class object could have an attribute state of color, speed and model values.

- Behavior : an object's behavior is defined by its services, that is, the methods that the object can call or that are automatically called by the object's creation. For instance, a Car object could probably be able to do some of these functions: accelerate, brake or say honk the horn.

Every object is different. This means that although objects that belong to the same class have the same behaviour and structure, different information (or state) can be held.

2.1 Instantiation and usage of instances

In order for you to instantiate an object in Java, you have to type the keyword `new`, class name, and make a constructor for that class. The `new` command makes some space in the memory of the computer where the object will be stored as well as aids in initializing the object according to the constructor of the class.

After an object has already been instantiated, it is used in getting its properties as well as invoking its methods, just like any object in the actual world. In most cases, an object is said to model certain items in your program such as a physical object, for example a car, a computer, and a more abstract object such as an employee or even a bank account.

3. Class and object relationships

The concept of a class and object has a close resemblance with the concept of a template and its reproduction, which is called a finished product – the object. Therefore once an object is created, it is filled with data in accordance with the template of the class. Class is used to define a general category while an object is used to define a sub-category.

- Class as a Model : Class gives a wide view of what will be the properties and functions of the entities it will encapsulate. But a class does not contain actual values; it is only when you instantiate objects that values are populated into class members.

- Object as Instance : A class can be instantiated when an object is created from it. So, each object has its own uniquely defined values for the attributes contained in that class, and can call the functions derived from that class.

In object-oriented programming, this kind of relationship is very important for structuring code in a scalable way. By defining classes and using objects to model them at a particular moment in time, you are able to provide a wide range of options while coding.

4. Real-World Analogy of Classes and Objects

There are many real life examples which can help us understand the relationship better, let's take the example of a house blueprint. In this example, the blueprint is the class and the house built based on the blueprint is the object. The blueprint has information about a house like its size, number of rooms, windows and doors, but it is not a house as such. So, the class is an abstraction that has information about the attributes and behaviors of physical objects but it is not an implementing object. So to use the blueprints to make a house means making an object of it.

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