Adding a feature

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        PracticeLog log = new PracticeLog();
        UserInterface ui = new UserInterface(scanner, log);
        ui.start();
    }
}

public class PracticeLog {
    private int totalMinutes;
    private int longestSession;
    private int sessions; // new

    public PracticeLog() {
        this.totalMinutes = 0;
        this.longestSession = 0;
        this.sessions = 0; // new
    }

    public void add(int minutes) {
        this.totalMinutes = this.totalMinutes + minutes;
        if (minutes > this.longestSession) {
            this.longestSession = minutes;
        }
        this.sessions++; // new
    }

    public int total() {
        return this.totalMinutes;
    }

    public int longest() {
        return this.longestSession;
    }

    public double average() { // new
        if (this.sessions == 0) {
            return 0;
        }
        return (double) this.totalMinutes / this.sessions;
    }
}

import java.util.Scanner;

public class UserInterface {
    private Scanner scanner;
    private PracticeLog log;

    public UserInterface(Scanner scanner, PracticeLog log) {
        this.scanner = scanner;
        this.log = log;
    }

    public void start() {
        while (true) {
            System.out.print("> ");
            String command = this.scanner.nextLine();
            if (command.equals("quit")) {
                System.out.println("Keep practicing!");
                break;
            }
            if (command.equals("log")) {
                int minutes = Integer.valueOf(this.scanner.nextLine());
                this.log.add(minutes);
                System.out.println("Logged " + minutes + " minutes");
            } else if (command.equals("total")) {
                System.out.println("Total: " + this.log.total() + " minutes");
            } else if (command.equals("longest")) {
                System.out.println("Longest: " + this.log.longest() + " minutes");
            } else if (command.equals("average")) { // new
                System.out.println("Average: " + this.log.average() + " minutes"); // new
            } else if (command.equals("help")) { // new
                System.out.println("Commands: log, total, longest, average, help, quit"); // new
            } else {
                System.out.println("Unknown command: " + command);
            }
        }
    }
}