Parameters and Return Values

Giving a method some information

Parameters are values you pass into a method, written inside the brackets with their type:

public class Main {
    static void greet(String name, int age) {
        System.out.println("Hi " + name + ", you are " + age);
    }

    public static void main(String[] args) {
        greet("Asha", 21);
        greet("Ravi", 34);
    }
}

Output

Hi Asha, you are 21
Hi Ravi, you are 34

Getting an answer back: return

Instead of void, write the type of the answer. return sends the answer back to whoever called the method:

public class Main {
    static int square(int n) {
        return n * n;
    }

    static double areaOfCircle(double radius) {
        return Math.PI * radius * radius;
    }

    public static void main(String[] args) {
        int s = square(6);
        System.out.println(s);
        System.out.println(square(3) + square(4));
        System.out.printf("%.2f%n", areaOfCircle(2));
    }
}

Output

36
25
12.57

Think of it like this: A method with return is like a juice machine: you put in fruit (the parameters) and get juice back (the return value).

Methods that answer yes or no

public class Main {
    static boolean isEven(int n) {
        return n % 2 == 0;
    }

    public static void main(String[] args) {
        for (int i = 1; i <= 4; i++) {
            if (isEven(i)) {
                System.out.println(i + " is even");
            }
        }
    }
}

Output

2 is even
4 is even

Remember: return ends the method straight away. Any code after it in the same block never runs.

Common mistake: If a method says it returns int, every path through it must return an int, otherwise you get a missing return statement error.