🚀 Day 5 of My Automation Journey – Instance, Static Variables & Operators in Java

Source: Dev.to

Instance Variables / Static Variables

• Static Variable: Belongs to the class, not to any individual object. It is common for all objects.
• Instance Variable: Each object gets its own copy.

Example – School Marks Program

package java_module_1;

public class School_Vikas {

    // Instance variables
    int tam_mark;
    int eng_mark;

    // Static variable
    static String School_Name = "Vikas School";

    public static void main(String[] args) {

        School_Vikas rajiv = new School_Vikas();
        rajiv.tam_mark = 60;
        rajiv.eng_mark = 50;

        System.out.println("Rajiv's Tamil mark is " + rajiv.tam_mark);
        System.out.println("Rajiv's English mark is " + rajiv.eng_mark);

        // Calling static variable
        System.out.println("School Name " + School_Vikas.School_Name);

        // Direct access inside the same class
        System.out.println(School_Name);

        School_Vikas kumar = new School_Vikas();
        kumar.tam_mark = 55;
        kumar.eng_mark = 45;

        System.out.println("Kumar's Tamil mark is " + kumar.tam_mark);
        System.out.println("Kumar's English mark is " + kumar.eng_mark);
    }
}

What Happens Here?

• Instance Variables: Each object (rajiv, kumar) has its own copy of tam_mark and eng_mark.
  • Memory (Heap):
    • rajiv → tam_mark = 60
    • kumar → tam_mark = 55
• Static Variable: Only one copy of School_Name exists, shared by all objects.
  • Stored in the class area (Method Area).

How to Access a Static Variable

School_Vikas.School_Name          // From outside the class
System.out.println(School_Name); // Directly inside the same class

Important Rule for Static Variables

• Created when the class is loaded.
• Does not require object creation.
• Stored in class memory (Method Area).

Why Use Static?

Use static when a value is common to all objects, e.g.:

• School name
• Interest rate (bank example)

Introduction to Operators in Java

An operator is a special symbol used to perform operations.

Types of Operators

1. Assignment Operator

   int a = 10;

2. Arithmetic Operators (+, -, *, /, %)

   int total = 10 + 5;

3. Unary Operators

   int a = 5;
   a++;   // Post Increment
   ++a;   // Pre Increment
   a--;   // Post Decrement
   --a;   // Pre Decrement

4. Relational Operators – used for comparison (==, !=, “, =).

5. Conditional (Logical) Operators

   • && → AND
   • || → OR

Key Takeaways – Day 5

• A static variable is shared by all objects of the class.
• Instance variables are unique to each object.
• Understanding operators is essential for performing calculations and logical checks in Java.

---

Note: I used ChatGPT to help structure and refine this blog.