Static Methods

Static Methods

1. What Static Means (beginner)

Static = belongs to class, not object. Call without new: Math.sqrt(16). Shared single copy (no this!). Utility functions live here!

2. Code — Counter Proof (static vs instance!)

class Demo {
    static int count = 0; // ONE copy (shared!)
    int id;               // per-object copy!
    Demo() { count++; id = count; }
    static int total() { return count; } // static (no object needed!)
    int getId() { return id; }           // instance (needs object!)
}
Demo a = new Demo(); Demo b = new Demo();
System.out.println(Demo.total()); // 2 (class call!)
System.out.println(a.getId() + " " + b.getId()); // 1 2 (separate!)
// System.out.println(Demo.getId()); // ERROR! (needs object!)

3. Rules (exam traps!)

• Static method: NO this, NO instance vars (no object to read from!). Can use static vars + params only.
• Static method CAN be called via object (a.total() compiles) but style police: use Demo.total().
• main is static (JVM calls without new!).

4. When Static?

Pure helpers (add, sqrt), factories, counters. Need object state? Instance!

5. Exam Points

• Static vs instance + counter program — 5-7 marks, very frequent.
• this ban in static — 3 marks, favourite error.