What is the usage of class in Java?

In Java, a class serves as a blueprint or template for describing the attributes and behaviors of objects. It outlines the various properties and methods needed to create an object.

The usage of the class includes the following aspects:

1. Definition of attributes: a class can define various properties of an object, also known as member variables. These attributes can be of primitive types (such as int, double, etc.) or objects of other classes.
2. Definition of method: a class can define various behaviors of an object, also known as member methods. By using methods, properties of an object can be manipulated and modified to achieve specific functionality.
3. Encapsulation of properties and methods: The class can use encapsulation to package properties and methods within the class, providing access to the external interface. Through encapsulation, the internal implementation details of an object can be hidden, thereby improving the security and maintainability of the code.
4. Creating objects: Through the class, specific objects can be created. By using the keyword “new” and the class name, space can be allocated in memory for the object and the class constructor method can be called to initialize the object.
5. Inheritance: A class can be used as the parent class for other classes. By inheriting, the child class can access the parent class’s attributes and methods, and even extend or override them. Inheritance allows for code reusability and extension.
6. Instantiation and statics: a class can define instance variables and static variables. Instance variables have a unique copy for each object, while static variables have only one copy at the time of class loading, shared by all objects.

In conclusion, the usage of classes in Java is to define the properties and behaviors of objects, to achieve encapsulation, inheritance, and polymorphism, and to create objects, access their attributes and methods. It is one of the fundamental concepts in Java and a core aspect of object-oriented programming.