Private members

Defining private properties

In Java, private are defined by using the private access modifier. This ensures that the property cannot be accessed or modified directly from outside the class.

public class SmartLight {
    private int brightness; // declare private property
    private String color;
    private boolean isOn;

    public SmartLight(String color, int brightness) {
        this.color = color;
        this.brightness = brightness;
        this.isOn = false;
    }

}

Private properties cannot be accessed directly

If we try to modify private properties directly, we will get an error because Java enforces access control at compile time:

java

public class Main {
    public static void main(String[] args) {
        SmartLight bathroomLight = new SmartLight("amber", 50);
        bathroomLight.brightness = 90; // Error
    }
}

output

Error: brightness has private access in SmartLight

Using private properties

Since private properties cannot be accessed directly from outside the class, we need to provide public methods to work with them.

SmartLight.java

public class SmartLight {
    private int brightness;
    private String color;
    private boolean isOn;

    public SmartLight(String color, int brightness) {
        this.color = color;
        this.brightness = brightness;
    }

    public int getBrightness() {
        if (this.isOn) {
            return this.brightness;
        } else {
            return 0;
        }
    }

    public void setBrightness(int newBrightness) {
        if (newBrightness < 0 || newBrightness > 100) {
            throw new IllegalArgumentException("Brightness must be between 0 and 100");
        }
        this.brightness = newBrightness;
    }

}

Main.java

public class Main {
    public static void main(String[] args) {
        SmartLight bedroomLight = new SmartLight("cool blue", 50);
        bedroomLight.setBrightness(90);
        System.out.println(bedroomLight.getBrightness()); // 90
    }
}

In this example, getBrightness() and setBrightness() are public methods that allow controlled access to the private brightness property.