Java · Lesson 9 of 15

Methods and Overloading

Parameters, return values, overloading, varargs and pass-by-value.

Beginner
12 min read
3 objectives

Before this lessonLesson 8: Arrays

What you will learn

Write methods with return types
Overload a method
Explain pass-by-value

Your Progress

0 of 15 lessons 0%

Lessons0 / 15
Completed0
Est. time left~ 4 hours

Create a free account to keep your progress on every device.

A method is a named block of code you can call again and again. It declares what it takes in (parameters) and what it gives back (return type), or void if nothing.

Parameters and return values

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

    static void greet(String name) {
        System.out.println("Hi " + name);
    }

    public static void main(String[] args) {
        greet("Ada");
        System.out.println(square(7));
    }
}

Output

Hi Ada
49

Overloading

Several methods can share a name if their parameter lists differ. The compiler picks the one that matches the call.

public class Main {
    static int add(int a, int b) { return a + b; }
    static double add(double a, double b) { return a + b; }
    static int add(int a, int b, int c) { return a + b + c; }

    public static void main(String[] args) {
        System.out.println(add(1, 2));
        System.out.println(add(1.5, 2.5));
        System.out.println(add(1, 2, 3));
    }
}

Output

3
4.0
6

Varargs

public class Main {
    static int sum(int... nums) {
        int total = 0;
        for (int n : nums) total += n;
        return total;
    }

    public static void main(String[] args) {
        System.out.println(sum());
        System.out.println(sum(1, 2, 3, 4));
    }
}

Output

0
10

Java is always pass-by-value

A method receives a copy of each argument. For primitives that copy is the number itself, so changing it does nothing to the caller. For objects the copy is the reference: the method can change the object's contents, but reassigning the parameter does not affect the caller's variable.

public class Main {
    static void change(int n, StringBuilder sb) {
        n = 99;
        sb.append("!");
        sb = new StringBuilder("other");
    }

    public static void main(String[] args) {
        int n = 1;
        StringBuilder sb = new StringBuilder("hey");
        change(n, sb);
        System.out.println(n + " " + sb);
    }
}

Output

1 hey!

Up next · Lesson 10Inheritance and Polymorphismextends, super, overriding and treating subclasses as their parent type.