Method Prototype

Method Prototype

1. What Is a Prototype? (beginner)

Prototype = method's signature line (promise!): return type + name + params, NO body. Like function declaration in C. Tells caller what to give, what comes back.

2. Anatomy (dissect one line!)

public static int add(int a, int b); // prototype (ends with ; — no body!)
// |      |      |   |   |_________|
// |      |      |   |   params (inputs with types!)
// |      |      |   name (verb, camelCase!)
// |      |      return type (output kind!)
// |      static (no object needed!)
// access (who can call!)

Full method = prototype + { body }. Interface/abstract use bare prototypes (body later!).

3. Code — Prototype vs Definition

class Calc {
    int add(int a, int b); // ERROR in class! (needs body — prototypes only in interface/abstract!)
}
interface Adder {
    int add(int a, int b); // OK! (interface = prototypes only, class implements!)
}
class MyCalc implements Adder {
    public int add(int a, int b) { return a + b; } // definition (body!)
}

4. Traps

• Class method needs body: int f(); in class = ERROR (add {} or make abstract!).
• main prototype fixed: public static void main(String[] args) (exam asks each word!).
• Overloading = same name, different params (different prototypes!).

5. Exam Points

• Dissect prototype (5 parts) — 3-5 marks, frequent.
• Prototype vs definition + interface use — 3 marks, frequent.