In this article we learn what is class in java, how to declare class and how to access members of the class.
What is Class in Java?
1. A class in Java is a blueprint which all the data.
2. It describes the state and behavior of a specific object.
3. In Java, we cannot declare a top-level class as private. Java allows only public and default access specifiers for top-level classes. We can declare inner classes as private.
4. We can include any type of the variables in Java – local, global variables.
5. There can be only one public class in a single program and its name should be the same as the name of the Java file. There can be more than one non-public classes in a single Java file.
6. A public class is visible to all classes from all the packages.
7. A class with default access is visible only to the classes within the same package.
8. We can also use the non-access modifiers for the class such as final, abstract and strictfp. This is called default/package accessibility.
9. We cannot create an object or instance of an abstract class.
10. No subclasses or child class can be created from a class that is declared as final.
11. A class cannot be declared both as final and abstract at the same time.
Syntax of Class in Java
class classname {
// member variable
// member functions
}
Can we declare a top-level class as protected or private in Java?
If a top-level class is declared as private the compiler will complain that the modifier private is not allowed here. This means that a top-level class cannot be a private, the same can be applied to protected access specifier also.
Declaration of Class in Java
In order to bring class into existence, we should declare it. We can declare a class with the use of a class keyword.
The components of the Java Class declaration are:
1. Access Modifiers: We can access Java classes using any access modifiers such as public, private, protected and default.
2. Class Name: In Java, the class name generally represents nouns which should begin with a capital letter without any spaces.
3. Superclass (if any): The name of the parent class is a superclass and its child class is a subclass, and child class inherits the properties of a parent using the extends keyword. A subclass can only inherit a single parent.
4. Interfaces (if any): To declare an interface, we just write the keyword interface followed by the interface name.
5. Class Body: The class body follows the class declaration and embeds within curly braces {}.
Accessing the members of a Class in Java:
We can access the data members of a class using the object of the class. We just write the name of the object which is followed by a dot operator then we write the name of the data member (either variables or methods) which we want to access.
Syntax of accessing data members and methods of a Java Class:
objectName.variableName; //accessing the variables
objectName.methodName(); //accessing the methods
Multiple Java Classes
Multiple classes means that we can create an object of a class and use it in another class. Also, we can access this object in multiple classes.