Method Signature

In a class with two students called Navika, the teacher adds a surname: Navika Anamaneni and Navika K. Java has the same problem with methods: a class can have several methods with the same name, so it needs something more to tell them apart. That something is the method signature: the method's name plus the types of its parameters, in order.

What's in the Signature

So fare(int, int) is the signature of static int fare(int km, int people).

Same Name, Different Signatures: Overloading

Because the signatures differ, a class can have several methods named fare. This is called method overloading:

public class Fares {
    static int fare(int km) {
        return km * 2;
    }
 
    static int fare(int km, int people) {
        return km * 2 * people;
    }
 
    static double fare(double km) {
        return km * 2.5;
    }
 
    public static void main(String[] args) {
        System.out.println(fare(100));
        System.out.println(fare(100, 3));
        System.out.println(fare(100.0));
    }
}

200
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250.0

How it works

1. The three signatures are fare(int), fare(int, int) and fare(double): all different.
2. For each call, the compiler picks the method whose parameters match the arguments: one int, two ints, or one double.
3. This choice happens at compile time.

Try it yourself: call fare(100L) with a long. Which method is chosen, and why? (Hint: a long can widen to double but not to int.)

When Signatures Clash

Changing only the return type doesn't make a new signature, so this doesn't compile:

O.java:3: error: method fare(int) is already defined in class O
    static double fare(int km) { return km; }
                  ^

The same happens if only the parameter names differ: fare(int km) and fare(int distance) have the same signature.

Common Mistakes

Thinking the return type distinguishes methods. It doesn't; the compiler wouldn't know which to call from fare(5);.

Overloads that differ only in parameter order of different types. book(int seat, String name) and book(String name, int seat) are legal but easy to call by accident. Avoid them.

Ambiguous calls. With show(long) and show(double), calling show(5) works (it picks long, the closer widening), but such overloads confuse readers.

Interview Corner

Practice

1. Easy: Write the signature of public static boolean isValid(String pin, int attempts).
2. Harder: Write three overloaded area methods: for a square (one double), a rectangle (two doubles) and a circle (one double named radius). Why doesn't the third compile, and how would you fix it?

Key Takeaways