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Dev Ananth Arul
Dev Ananth Arul

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Java Class, Object and Variables

Java Classes:
In Java, a class serves as a blueprint or a template for creating objects. It is a fundamental concept in object-oriented programming (OOP) and defines the structure and behavior that objects of that class will possess.

A class is a template to create objects having similar properties and behavior, or in other words, we can say that a class is a blueprint for objects.
Properties of Java Classes:

  • Class is not a real-world entity. It is just a template or blueprint, or a prototype from which objects are created.
  • A class itself does not occupy memory for its attributes and methods until an object is instantiated.
  • A Class in Java can contain Data members, methods, a Constructor, Nested classes, and interfaces.

Java Objects:

Objects are the instances of a class that are created to use the attributes and methods of a class. A typical Java program creates many objects, which as you know, interact by invoking methods. An object consists of:

State: It is represented by attributes of an object. It also reflects the properties of an object.
Behavior: It is represented by the methods of an object. It also reflects the response of an object with other objects.
Identity: It gives a unique name to an object and enables one object to interact with other objects.
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Java Variables:

In Java, variables are containers used to store data in memory. Variables define how data is stored, accessed, and manipulated.

A variable in Java has three components,

Data Type: Defines the kind of data stored (e.g., int, String, float).
Variable Name: A unique identifier following Java naming rules.
Value: The actual data assigned to the variable.
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Rules to Name Java Variables:

  • Start with a Letter, $, or _ – Variable names must begin with a letter (a–z, A–Z), dollar sign $, or underscore _.
  • No Keywords: Reserved Java keywords (e.g., int, class, if) cannot be used as variable names.
  • Case Sensitive: age and Age are treated as different variables.
  • Use Letters, Digits, $, or _ : After the first character, you can use letters, digits (0–9), $, or _.
  • Meaningful Names: Choose descriptive names that reflect the purpose of the variable (e.g., studentName instead of s).
  • No Spaces: Variable names cannot contain spaces.
  • Follow Naming Conventions: Typically, use camelCase for variable names in Java (e.g., totalMarks).

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