Static properties

Defining static properties

Let's add a static property to our camera class which holds information about the IP range cameras are allowed to use.

SmartCamera.java

public class SmartCamera {
    public static String networkPrefix = "192.168.12";

    private String location;
    private int batteryLife;

    public SmartCamera(String location) {
        this.location = location;
        this.batteryLife = 100;
    }
}

Main.java

public class Main {
    public static void main(String[] args) {
        System.out.println(SmartCamera.networkPrefix); // 192.168.12
    }
}

The networkPrefix property is accessed from the class itself, not an instance of the class. This ensures that all camera IP addresses begin with 192.168.12.

Using static properties

Often, we want to use static properties from within the class. We can do this by referencing the class itself inside the class.

SmartCamera.java

public class SmartCamera {
    public static String networkPrefix = "192.168.12";
    public static int host = 1;

    private String location;
    private int batteryLife;
    private String ipAddress;

    public SmartCamera(String location) {
        this.location = location;
        this.batteryLife = 100;

        // assign an IP address
        this.ipAddress = SmartCamera.networkPrefix + "." + SmartCamera.host;

        // increment host number for the next camera
        SmartCamera.host++;
    }

    public getIpAddress() {
      return this.ipAddress;
    }
}

Main.java

public class Main {
    public static void main(String[] args) {
        SmartCamera gardenCam = new SmartCamera("Garden");
        SmartCamera loungeCam = new SmartCamera("Living Room");

        System.out.println(gardenCam.getIpAddress()); // 192.168.12.1
        System.out.println(loungeCam.getIpAddress()); // 192.168.12.2
    }
}

Static methods

Classes can have static methods too! This is useful for defining actions that affect the whole class of cameras. For example, resetting the IP range.

SmartCamera.java

public class SmartCamera {
    public static String networkPrefix = "192.168.12";
    public static int host = 1;

    private String location;
    private int batteryLife;
    private String ipAddress;

    public static void resetHost() {
        SmartCamera.host = 1;
    }

    public SmartCamera(String location) {
        this.location = location;
        this.batteryLife = 100;
        this.ipAddress = SmartCamera.networkPrefix + "." + SmartCamera.host;
        SmartCamera.host++;
    }

}

Main.java

public class Main {
    public static void main(String[] args) {
        SmartCamera gardenCam = new SmartCamera("Garden");
        SmartCamera loungeCam = new SmartCamera("Living Room");
        System.out.println(SmartCamera.host); // 3

        // Resetting the host
        SmartCamera.resetHost();
        System.out.println(SmartCamera.host); // 3
    }
}