Methods that return a value

In module 17 the methods of your classes did something: they printed, or they changed the object's instance variables. They were all void. An object's method can also return a value, just like the methods of module 11. This basket counts its fruit:

public class Main {
    public static void main(String[] args) {
        Basket basket = new Basket();
        System.out.println(basket.isEmpty());
        basket.addApples(3);
        basket.addPears(2);
        int fruit = basket.total();
        System.out.println("Fruit in the basket: " + fruit);
        System.out.println(basket.isEmpty());
    }
}

public class Basket {
    private int apples;
    private int pears;

    public Basket() {
        this.apples = 0;
        this.pears = 0;
    }

    public void addApples(int count) {
        this.apples = this.apples + count;
    }

    public void addPears(int count) {
        this.pears = this.pears + count;
    }

    public int total() {
        return this.apples + this.pears;
    }

    public boolean isEmpty() {
        return this.apples + this.pears == 0;
    }
}

true
Fruit in the basket: 5
false

• public int total() returns an int: the apples and pears of this basket added up. There's no static in the header, because the method belongs to an object and works with that object's own variables.
• In main, the call basket.total() stands for the value it returns. Here main stores it in fruit, but the call can go anywhere a value can: in a print line, a calculation or a comparison.
• isEmpty() returns a boolean, so its call works as a condition on its own: if (basket.isEmpty()) { ... }. A method that answers a yes-or-no question usually has a name that starts with is or has, such as isEmpty or hasRoom.

You've used methods like these on lists and strings: list.size() returns how many values a list has, and word.isEmpty() tells whether a string is empty. Now your own classes can have them too.

Why return the value instead of printing it? For the same reason as in module 11: the caller decides what to do with it. main can compare the totals of two baskets, add them up, or print them in its own words.