Lesson 4 of 26By Simplilearn
Last updated on Jul 10, 20207564Java is one of the most influential and leading programming languages available today, reaching this milestone courtesy of its object-oriented nature. Java is organized in such a way that everything you program in it becomes either a class or an object. Many beginning programmers want to be proficient with Java-based building blocks, and this article’s purpose is to help reach that goal.
The article breaks down into the following sections:
Classes and objects are the two most essential Java concepts that every programmer must learn. Classes and objects are closely related and work together. An object has behaviors and states, and is an instance of class. For instance, a cat is an object—it’s color and size are states, and its meowing and clawing furniture are behaviors. A class models the object, a blueprint or template that describes the state or behavior supported by objects of that type.
Let’s explore Java classes and objects in a bit more detail, starting with the class.
We can define a class as a container that stores the data members and methods together. These data members and methods are common to all the objects present in a particular package.
Every class we use in Java consists of the following components, as described below:
Object-oriented programming languages like Java provide the programmers with four types of access modifiers.
These access modifiers specify the accessibility and users permissions of the methods and members of the class.
This describes the name given to the class that the programmer decides on, according to the predefined naming conventions.
The body of the class mainly includes executable statements.
Apart from these, a class may include keywords like "super" if you use a superclass,
"implements" if you are inheriting members, methods, and instances from the same class, and
"interface" if you are inheriting any members, methods, and instances from a different class.
In Java, we classify classes into two types:
Built-in classes are just the predefined classes that come along with the Java Development Kit (JDK). We also call these built-in classes libraries. Some examples of built-in classes include:
User-defined classes are rather self-explanatory. The name says it all. They are classes that the user defines and manipulates in the real-time programming environment. User-defined classes are broken down into three types:
Concrete class is just another standard class that the user defines and stores the methods and data members in.
Syntax:
class con{
//class body;
}
Abstract classes are similar to concrete classes, except that you need to define them using the "abstract" keyword. If you wish to instantiate an abstract class, then it should include an abstract method in it. Otherwise, it can only be inherited.
Syntax:
abstract class AbstClas{
//method();
abstract void demo();
}
Interfaces are similar to classes. The difference is that while class describes an object’s attitudes and behaviors, interfaces contain the behaviors a class implements. These interfaces will only include the signatures of the method but not the actual method.
Syntax:
public interface demo{
public void signature1();
public void signature2();
}
public class demo2 implements demo{
public void signature1(){
//implementation;
}
public void signature2(){
//implementation;
}
}
You can define a typical class in Java using the following syntax:
<Access Specifier> class <class name>{
//Body
}
Example:
public class Student{
String Name;
int rollno;
String section;
void study() {
}
void write() {
}
void play() {
}
}
The following rules are mandatory when you're working with Java classes:
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An object in Java is the most fundamental unit of the object-oriented programming paradigm. It includes the real-world entities and manipulates them by invoking methods. An object in Java consists of the following:
This is the unique name given by the user that allows it to interact with other objects in the project.
Example:
Name of the student
The behavior of an object is the method that you declare inside it. This method interacts with other objects present in the project.
Example:
Studying, Playing, Writing
The parameters present in an object represent its state based on the properties reflected by the parameters of other objects in the project.
Example:
Section, Roll number, Percentage
As discussed before, a class is a blueprint of any object. So, once you declare the class, all that you need to do to create a class is to instantiate it. There are three stages involved in creating an object. They are:
Example:
public class Student {
public Student (String name) {
System.out.println("parameters sent are :" + name );
}
public static void main(String []args) {
Student mystudent = new Student( "Steven" );
}
}
Output:
Steven
The key differences between a class and an object are:
And this brings us to the end of the article. We hope it has strengthened your understanding of the essential concepts relating to Java objects and classes, the rules used to declare them, and their key differences.
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