BPSC Assistant Programmer (ICT) Written Test: 2019প্রশ্ন ও সমাধান

Method overloading is defining multiple methods in the same class with the same name but a different parameter list (different number, type, or order of parameters). It is a compile-time (static) form of polymorphism — the compiler decides which version to call based on the arguments supplied.

Example (Java):

class Calculator {
    int add(int a, int b) { return a + b; }              // 2 int params
    double add(double a, double b) { return a + b; }      // 2 double params
    int add(int a, int b, int c) { return a + b + c; }    // 3 params
}
public class Main {
    public static void main(String[] args) {
        Calculator c = new Calculator();
        System.out.println(c.add(2, 3));        // calls int version -> 5
        System.out.println(c.add(2.5, 3.5));    // calls double version -> 6.0
        System.out.println(c.add(1, 2, 3));      // calls 3-arg version -> 6
    }
}

Rules:

• The return type alone cannot distinguish overloaded methods — the parameter list must differ.
• Overloading is resolved at compile time, unlike overriding which is resolved at run time.

Why it's useful: it lets a class expose one intuitive method name (e.g. add) for logically the same operation, regardless of the data types or argument count the caller has on hand — improving readability and API design.

Exam takeaway: Overloading = same name, different signature, same class, compile-time binding; don't confuse it with overriding (same name and signature, subclass redefines a superclass method, run-time binding).

Hub, switch, and router are all connectivity devices but operate at different OSI layers with very different intelligence.

Aspect	Hub	Switch	Router
OSI Layer	Physical (Layer 1)	Data Link (Layer 2)	Network (Layer 3)
Addressing used	None	MAC address	IP address
Traffic handling	Broadcasts to all ports	Forwards only to the destination MAC's port	Routes packets between different networks
Collision domain	Single, shared	Separate per port	Separate per port/network
Intelligence	None (electrical repeater)	Learns MAC-to-port mapping	Maintains routing tables, picks best path
Typical use	Legacy, rarely used today	Connects devices within one LAN	Connects different networks (LAN to LAN/WAN/Internet)

graph LR
  PC1[PC 1] --- SW[Switch]
  PC2[PC 2] --- SW
  PC3[PC 3] --- SW
  SW --- R[Router]
  R --- WAN((Internet / Other Network))

Why it matters: a hub floods every packet to every port (wasting bandwidth, causing collisions); a switch intelligently forwards only to the intended device using its MAC address table; a router goes further, connecting entirely separate IP networks and choosing paths between them.

Exam takeaway: Hub = dumb repeater (L1), Switch = smart LAN traffic director (L2, MAC-based), Router = inter-network path-chooser (L3, IP-based) — going from least to most "intelligent."