A class in programming is a grouping of data, fields, and functions or methods. They are all called variables, methods, or member functions. The program is built from a set of classes. Once it is defined and implemented, you can declare its elements in the same way as language variables from the primitive types “int”, “double” and “String”.
A brief history of the programming language
SIMULA was the first object language used to create simulations. Alan Kay, who was studying at the University of Utah at that time, liked the language because in the future it could be used for a personal computer in order to implement graphically-oriented applications. He suggested that a language such as SIMULA would provide beginners with a good way to create programs, and shared his vision with Xerox Parc. In the early 1970s, a team led by Alan Kay created the first PC called Dynabook with the object-oriented language Smalltalk, which exists to this day, although it is not particularly widely used for commercial purposes.
The idea of object-oriented programming (OOP) was developed in the 1970s, and in the early 1980s, Bjorn Straustrup integrated it into the C language, which became known as "C ++" - the first object-oriented language (OOY), widely used in commercial purposes.
In the early 1990s, a group at Sun, led by James Gosling, developed a simpler version of C ++ called Java. Which was supposed to be the language for video-on-demand applications. This Java programming project from scratch has never been implemented. The group was forced to refocus on developing a language for Internet applications. It began to gain more and more popularity as the Internet developed, although its penetration into the market was rather restrained due to apparent inefficiency.
Object oriented modeling
Classes and objects are two of the few key building blocks of OOP. They are used to model behavior and encapsulation. In the real world, you can find many separate objects of the same type. For example, there are thousands of bicycles of the same make and model. Each was built from one set and, therefore, contains equal components. In OO terms, this means that a bicycle is an instance of a class of objects known as bicycles. Everything is simple. A class in programming languages is a plan for creating specific objects. For example, Bicycle is one of the possible implementations.
You may notice that the Bicycle class does not contain the "main" method. Due to the fact that he does not present a complete application, but only a plan for bicycles. The responsibility for creating and using new Bicycle objects belongs to another class in programming. And the Bicycle Demo is the one that creates two separate Bicycle objects and calls their methods.
The output from this test displays the final speed and gear for two bikes.
Key Terms
A variable is a name with a value that can change throughout the program. According to the information contained, they are classified into 2 or more types, depending on the language used. In general, there are 2 types of classifications:
- Variables of primitive types. They are determined by a single value - an integer, floating point, symbol or logical sign.
- Reference variables are the names of more complex information: arrays or objects of a particular class.
The key point of OOP is to prevent incorrect information, since the variables were not correctly initialized. For the correct definition of objects, you must use the constructor — methods, which works automatically every time an object is created. Their main mission is to reserve memory, to initialize the variable members of the class in programming. They do not have a void return value, and their name matches the name of the common group. Its implicit argument is the object that is being created.
Classes and Objects in Python
Python refers to OO programming languages, thereby differing from procedurally oriented, where the main emphasis is on functions, it is based on objects. An object is a set of data and functions that affect them. A class is a plan for an object. You can think of the classroom as a sketch (prototype) of a house. It contains all the details about floors, doors, windows and other structures. Based on these descriptions, a house is built that is an object.
An object is simply a set of data and methods (functions) that affect these. A class is a plan for an object. You can think of the classroom as a sketch (prototype) of a house. It contains all the details about floors, doors, windows and other structures. Based on these descriptions, a house is built that is an object.
Since you can make many houses from the description, it is possible to create many objects from one group. It is also called an instance. What do we have in the end? That process demonstrates the concept of an instance of a class and its creation. Just as function definitions begin with the keyword def, Python defines a group using class. The first line is called "docstring" and has a brief description of the class.
The class creates a new local namespace in which all its attributes are defined, they can be data or functions. It also has special ones starting with double underscores (__). For example, "__doc__" gives the document string of this class in programming.
Once defined, a new object with the same name is created. It allows you to access various attributes, as well as create new objects of this class.
Keyword "class"
Python is a great language that supports OOP; it is used to set the class. It offers a number of advantages over other Java, C ++, or R. It is a dynamic language with high-level data types, so development is much faster than with Java or C ++. The programmer is not required to declare the types of variables and arguments. It also makes Python easy for beginners to understand and learn, its code more readable and intuitive.
To define a class in Python, you can use the class keyword, followed by a name and a colon. Inside its "__init__" method must be defined with "def". This is an initializer that can later be used to create objects; it must always be present. This is similar to a Java constructor.
It takes one argument, "self," which refers to the object itself. Inside the method, the pass keyword is used, and the correct indentation is applied. "Self" in Python is equivalent to "this" in C ++ or classes in Java. In this case, there is basically an empty “Dog”, but not yet an object. The class has precise specifications, like a plan or template. They establish a class contract.
Breakdown of view
The class can be divided into two parts:
- The class header, which consists of the keyword "class" and the name that is assigned to it. Names in programming languages are also known as identifiers.
- A body that consists of a pair of opening / closing wavy brackets with elements between them.
Here is the template for the class source code:
class
{
...
}
When a class is written, it is replaced with a name. A body consists of one or more elements, a string means any number of preceding parts. In particular, the keyword “class” should begin with the first column of the row, followed by the rest of the header information — an identifier in the simplest case.
An open wavy bracket delimits the header and initiates the body of the class. Some programmers like to place it at the end of a line, but most like it on a separate line. A wavy bracket limits the body of the class. A common practice is to put the closing bracket in the column separately.
Item collection
The contents of the class body consist of a collection of elements. Members of variables called fields, and the parts that it makes, denoted by methods also known as procedures.
Body content must be indented by at least two columns. Many programmers make them four columns at a time to make it easier to read the source code. The quantity does not matter, but must match any selected amount.
There is another rule that needs to be followed: class identifiers must start with a capital letter, just like every new word in it.
Classes are made up of elements. Members are either fields or methods. Each software must have a special method called “main”, if you combine the source code, you get a template for a minimal application.
This is the de facto standard where names begin with a capital letter, as well as additional words in it. For example: MyClass is suitable, but myClass and Myclass are not. The class identifier must also be the name of the file into which the source code is entered. It must have the extension ".java".
Keywords
Class keywords in Java are words reserved as the basic building blocks of a language. You cannot use them for the names of created objects. Such as identifiers of classes, fields and methods. The compiler recognizes these words and treats them as special ones.
When the Java application is running, the java command is used, which launches the JVM, and indicates the class file to execute it. The process begins with a special method, which the user defines as the “main” method of the application. This convention is a tradition of Java programming from scratch, inherited from "C".
The source code for “main” () always looks something like this:
public static void main (String [] identifier)
{
...
}
The key "public" and "static", as special modifiers, to find the "main" were found and available. An identifier can be anything, but to a large extent - the standard uses the name "arg", which is an abbreviation for the arguments.
Java class constructor
"Class" can be understood as a prototype that regulates variables and methods common to a particular type of instance; it defines everything that characterizes and can create one or more instances. It sets the variables and methods common to instances of this type created by the class, but then each will have its own values: template, color, and recipe.
In Java, a class is first created before it can be instantiated. An object becomes an instance of a class. It contains attributes and methods, when creating, you need to specify the types, methods, functions and name of the attributes, as well as the data type, names and other parameters that they use.
The basic structure looks like this.
JavaScript was created with the class name "MyClass", which has a total of three attributes, and all of them are private: "String", "int" and "float".
Limit variable
C storage classes are used to describe variable functions. They mainly include the scope, visibility and lifetime, which help to track the existence of a particular variable during program execution.
C uses 4 storage classes. Namely:
- Auto - set by default for all variables declared inside a function or class block in C. Therefore, the keyword “auto” is rarely used when writing C programs. Access to automatic variables is possible only inside the block / function in which they were declared, and not outside them, which determines their scope. Of course, you can access them nested inside the parent block / function in which the automatic variable was declared. However, they can also be accessed outside their scope, indicating a very precise place in memory where they are located.
- External when a variable is defined elsewhere rather than where it is used. Typically, a value is assigned in one block, and this can be overwritten in another. Thus, extern is nothing more than a global variable initialized with a valid value in which it is declared for use elsewhere.
- Static, is used to declare static variables, which are widely used when writing classes in C. They tend to retain their value even after they go beyond the scope. Thus, we can say that they are initialized only once and exist until the program terminates, they are not allocated new memory, since they are not re-declared, and the scope depends on the function for which they were defined. Global static variables can be accessed anywhere in the program. By default, they are set to 0 by the compiler.
- Register, declares variables that have the same functionality as automatic ones. The only difference is that the compiler tries to store them in the microprocessor if access is free. This makes use much faster than in memory at run time. If a free register is not available, they are stored only in memory. Typically, the few variables that need to be accessed very often in a program are declared with the “register” keyword, which improves program execution time.
Syntax: storage class var_data_type variable_name.
Programming secrets
The following recommendations are not exhaustive and are intended for the correct use of object-oriented programming design patterns:
- Avoid omnipotent classes in Python.
- Use meaningful names.
- When developing a class or refactoring existing code, the developer must make a list of all tasks and come up with a name.
- When using OOP, it is much easier to come up with meaningful names, since the design pattern itself often determines the type of responsibility.
- The class name must begin with a capital letter. If the name represents a compound word or several words, then the first letter of each word must be uppercase. Example: class Study, class StudyTonight etc.
- Classes contain data members and member functions. And access to these elements and a variable depends on qualifiers.
- The concept of class members. What does it mean? A class in C ++ is similar to structures in C. The only difference is that it uses private access control by default, and the structure is public.
- All OOPS functions revolve around classes in C - inheritance, encapsulation, abstraction, and others.
- Objects contain separate copies of member data.
- You can create as many objects as you need.
An object has individual variables. They are initialized using special class functions called constructors. And whenever it goes out of scope, another special function called Destructor is called to free the memory reserved by the object. C ++ does not have an automatic garbage collector, as in JAVA, in it Destructor performs this task.
The article is written in simple language about classes in programming. We hope the material was clear to you. Knowledge of the rules for using object-oriented languages is the main condition for developing a successful application. Good architecture means money saved by training, maintaining, testing, fixing, expanding, and scaling source code. It takes more time and concern for the initial development, but quickly returns an investment with great interests. Inevitably, even better-engineered architectures need to be temporarily adjusted and refactored.