Java Variables – Kya Hote Hain?
Java mein variable ek aisa container hota hai jisme hum data store karte hain. Jaise school bag mein books rakhte ho, waise hi variable mein value rakhi jaati hai.
Har variable ka:
- Naam (name) hota hai
- Data type hota hai (jaise
int,String) - Aur usme value store hoti hai
Example:
int age = 21;
String name = "Rahul";
boolean isStudent = true;
Yahan age, name, aur isStudent teen variables hain.
Variable Declare Karne Ka Syntax
data_type variable_name = value;
Example:
float marks = 95.5f;
Constants in Java – Final Keyword ka Role
Jab aap chahte ho ki koi variable ki value kabhi change na ho, toh aap use constant bana sakte ho using the final keyword.
Matlab ?: Ek baar value assign kar di, fir use change karne ki permission nahi hoti.
Syntax:
final data_type variable_name = value;
Example:
final double PI = 3.14159;
Ab agar aap PI ki value change karne ki koshish karenge, toh compiler error dega:
PI = 3.14; // Error: cannot assign a value to final variable
Variable vs Constant
Variable: Value change ho sakti hai
Constant (final): Value fix rehti hai
Example:
int speed = 40;
speed = 60; // allowed
final int MAX_SPEED = 120;
MAX_SPEED = 150; // not allowed
Final Keyword Aur Kaha Use Hota Hai?
final keyword sirf variables ke liye nahi, balki:
- final class – use extend nahi kiya ja sakta
- final method – use override nahi kiya ja sakta
- final variable – uski value change nahi hoti
Conclusion
Java mein variables data store karne ke liye use hote hain jabki constants un data ke liye use hote hain jo fix hone chahiye. Agar aap chaahte ho ki koi value kabhi accidentally bhi na badle – jaise PI, GST_RATE, ya MAX_USERS – toh use final keyword lagakar constant bana do.
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