Static vs Non-Static in JAVA

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Static vs Non-Static in Java

When learning Java, one very important concept is Static vs Non-Static (Instance).
If you understand this clearly, Java and OOP will become much easier.

What is Static?

static is a keyword used to create variables or methods that belong to the class, not to objects.

Example:

class Student {
    static String college = "ABC College";
}

Access:
System.out.println(Student.college);

Key Idea:

Only one copy is created
Shared by all objects
No need to create an object

What is Non-Static? (Instance)

Non-static means it belongs to an object (instance).

Example:

class Student {
    int id;
    String name;
}

Access:

Student s1 = new Student();
s1.id = 101;
s1.name = "Ram";

** Key Idea:**

Each object has its own copy
Must create an object to use it

✔️ rollNo, name → Non-static
✔️ college → Static

When to Use Static?

Use static when data is common for all objects:

Shared values
Utility methods
Constants

When to Use Non-Static?

Use non-static when data is different for each object:

Student name
Employee salary
Product details

Important Rule

A static method cannot directly access non-static variables

Wrong:

class Test {
    int x = 10;

    static void show() {
        System.out.println(x); // Error
    }
}

Correct:

class Test {
    int x = 10;

    static void show() {
        Test obj = new Test();
        System.out.println(obj.x);
    }
}

Real-Life Example

College System

class Student {
    int rollNo;                 // Unique for each student
    String name;                // Unique for each student
    static String college = "ABC"; // Same for all students
}