Java Project: Simple Alarm Clock

Alarm Clock using Java Timer and TimerTask:

Simple Alarm Clock:

Input: Set the alarm time and optional message.
Output: Alarm triggered at the set time with a notification.

Example:

• Input: "Set alarm for 7:00 AM"
• Output: "Alarm set for 7:00 AM."
  At 7:00 AM: "Wake up! It's 7:00 AM."

Solution 1: Simple Alarm Clock using Timer and TimerTask

Code:

import java.util.Timer;
import java.util.TimerTask;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Scanner;

public class SimpleAlarmClock {

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        // Input time for the alarm
        System.out.println("Set alarm time in format HH:mm (24-hour format): ");
        String alarmTime = scanner.nextLine();

        // Input optional alarm message
        System.out.println("Enter an optional alarm message (or leave blank): ");
        String message = scanner.nextLine();
        if (message.isEmpty()) {
            message = "Wake up!";
        }

        // Schedule the alarm
        scheduleAlarm(alarmTime, message);
        scanner.close();
    }

    // Method to schedule alarm using Timer
    public static void scheduleAlarm(String alarmTime, String message) {
        Timer timer = new Timer();

        // TimerTask to trigger alarm at set time
        TimerTask task = new TimerTask() {
            public void run() {
                System.out.println(message);
                timer.cancel(); // Stop the timer after the alarm
            }
        };

        try {
            // Parse the user input time
            SimpleDateFormat dateFormat = new SimpleDateFormat("HH:mm");
            Date alarmDate = dateFormat.parse(alarmTime);
            
            System.out.println("Alarm set for " + alarmTime);

            // Schedule task at the specified alarm time
            timer.schedule(task, alarmDate);
        } catch (Exception e) {
            System.out.println("Invalid time format. Please use HH:mm.");
        }
    }
}

Output:

Set alarm time in format HH:mm (24-hour format): 
 15:53
Enter an optional alarm message (or leave blank): 
 
Alarm set for 15:53
Wake up!

Explanation :

• Imports Timer and TimerTask for scheduling tasks.
• Takes user input for alarm time (in 24-hour format) and an optional message.
• Parses the input time using SimpleDateFormat and sets a TimerTask to print the message at the specified time.
• Once the task is triggered, it cancels the timer to stop further execution.

Solution 2: Simple Alarm Clock using ScheduledExecutorService

Code:

import java.time.LocalTime;
import java.time.temporal.ChronoUnit;
import java.util.Scanner;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

public class AlarmClock {

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        // Input time for the alarm
        System.out.println("Set alarm time in format HH:mm (24-hour format): ");
        String alarmTime = scanner.nextLine();

        // Input optional alarm message
        System.out.println("Enter an optional alarm message (or leave blank): ");
        String message = scanner.nextLine();
        if (message.isEmpty()) {
            message = "Wake up!";
        }

        // Schedule the alarm
        scheduleAlarm(alarmTime, message);
        scanner.close();
    }

    // Method to schedule alarm using ScheduledExecutorService
    public static void scheduleAlarm(String alarmTime, String message) {
        ScheduledExecutorService scheduler = Executors.newScheduledThreadPool(1);

        try {
            // Parse input time to LocalTime
            LocalTime alarmLocalTime = LocalTime.parse(alarmTime);
            LocalTime currentTime = LocalTime.now();

            // Calculate delay in seconds
            long delay = ChronoUnit.SECONDS.between(currentTime, alarmLocalTime);
            if (delay < 0) {
                System.out.println("Alarm time is in the past. Please set a future time.");
                return;
            }

            System.out.println("Alarm set for " + alarmTime);

            // Schedule the alarm task
            scheduler.schedule(() -> {
                System.out.println(message);
                scheduler.shutdown(); // Shut down the scheduler after the alarm
            }, delay, TimeUnit.SECONDS);
        } catch (Exception e) {
            System.out.println("Invalid time format. Please use HH:mm.");
        }
    }
}  

Output:

Set alarm time in format HH:mm (24-hour format): 
 15:45
Enter an optional alarm message (or leave blank): 
 Good Morning!
Alarm set for 15:45

Explanation:

• Uses ScheduledExecutorService for more robust task scheduling.
• Takes user input for alarm time and optional message.
• Converts the alarm time to LocalTime, calculates the delay between the current time and alarm time.
• Schedules the alarm task to run after the calculated delay, using TimeUnit.SECONDS.