Getters

Private variables

Module 17 kept every instance variable private, so that only the class's own code can change it. Private also means code outside the class can't even read it: basil.height in main doesn't compile (height has private access in Plant). But main often has a good reason to read a value, for example to compare two plants.

Getters

The way in is a method of the class that returns the value. A method whose only job is to return an instance variable is called a getter. It's named get followed by the variable's name with a capital letter: getHeight() for height.

public class Main {
    public static void main(String[] args) {
        Plant basil = new Plant("basil", 12);
        Plant fern = new Plant("fern", 30);
        basil.grow(5);
        System.out.println("The " + basil.getName() + " is " + basil.getHeight() + " cm");
        if (fern.getHeight() > basil.getHeight()) {
            System.out.println("The " + fern.getName() + " is taller");
        }
    }
}

public class Plant {
    private String name;
    private int height;

    public Plant(String name, int height) {
        this.name = name;
        this.height = height;
    }

    public void grow(int cm) {
        this.height = this.height + cm;
    }

    public String getName() {
        return this.name;
    }

    public int getHeight() {
        return this.height;
    }
}

The basil is 17 cm
The fern is taller

• Code outside the class can now read the height, but it still can't set it. The height changes only through the class's own methods, such as grow, so the class stays in charge of its data.
• A getter is an ordinary method that returns a value, so basil.getHeight() can go in a print line, a comparison or a calculation.
• The getter of a boolean variable is usually named with is: a variable private boolean ripe gets public boolean isRipe().

Setters

A method that gives a variable a new value is a setter:

public void setName(String name) {
    this.name = name;
}

Write a setter only when other code really needs to change that value freely. A method with a meaning, such as grow(5), is often better than setHeight(...): it says what happens, and the class can check the value, as cut did in module 17. A class doesn't need a getter and a setter for every variable either, only for the ones its users need.