Practical No. 15: Design and develop a simple countdown timer.

 

Practical No. 15: Design and develop a simple countdown timer.

Objective:

Develop a countdown timer where the user can enter the desired time (in minutes).
The app should display countdown using the CountDownTimer class.

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1. Project File Structure (Tree Diagram)

CountdownTimerApp/
│
├── app/
│   ├── src/main/
│   │   ├── java/com/example/countdowntimer/
│   │   │   └── MainActivity.java
│   │   │
│   │   ├── res/
│   │   │   ├── layout/
│   │   │   │   └── activity_main.xml
│   │   │   │
│   │   │   └── values/
│   │   │       └── strings.xml
│   │   │
│   │   └── AndroidManifest.xml

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2. activity_main.xml (User Interface)

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:gravity="center"
    android:padding="20dp">

    <!-- Student Name -->
    <TextView
        android:id="@+id/tvStudent"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/student_name"
        android:textSize="18sp"
        android:textStyle="bold"
        android:layout_marginBottom="20dp"/>

    <!-- Input Minutes -->
    <EditText
        android:id="@+id/etMinutes"
        android:layout_width="200dp"
        android:layout_height="wrap_content"
        android:hint="Enter minutes"
        android:inputType="number"
        android:layout_marginBottom="20dp"/>

    <!-- Timer Display -->
    <TextView
        android:id="@+id/tvTimer"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="00:00"
        android:textSize="40sp"
        android:textStyle="bold"
        android:layout_marginBottom="30dp"/>

    <!-- Start Button -->
    <Button
        android:id="@+id/btnStart"
        android:layout_width="200dp"
        android:layout_height="wrap_content"
        android:text="Start Timer"/>

    <!-- Reset Button -->
    <Button
        android:id="@+id/btnReset"
        android:layout_width="200dp"
        android:layout_height="wrap_content"
        android:text="Reset"
        android:layout_marginTop="10dp"/>

</LinearLayout>

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3. MainActivity.java (Complete Logic)

package com.example.countdowntimer;

import android.os.Bundle;
import android.os.CountDownTimer;
import android.text.TextUtils;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

import androidx.appcompat.app.AppCompatActivity;

import java.util.Locale;

public class MainActivity extends AppCompatActivity {

    private TextView tvTimer;
    private EditText etMinutes;
    private Button btnStart, btnReset;

    private CountDownTimer countDownTimer;
    private long timeLeftMillis = 0;
    private boolean timerRunning = false;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        tvTimer = findViewById(R.id.tvTimer);
        etMinutes = findViewById(R.id.etMinutes);
        btnStart = findViewById(R.id.btnStart);
        btnReset = findViewById(R.id.btnReset);

        updateTimerText();

        btnStart.setOnClickListener(v -> startTimer());
        btnReset.setOnClickListener(v -> resetTimer());
    }

    private void startTimer() {

        if (timerRunning) {
            Toast.makeText(this, "Timer already running", Toast.LENGTH_SHORT).show();
            return;
        }

        String input = etMinutes.getText().toString().trim();

        if (TextUtils.isEmpty(input)) {
            Toast.makeText(this, "Please enter minutes", Toast.LENGTH_SHORT).show();
            return;
        }

        int minutes = Integer.parseInt(input);

        if (minutes <= 0) {
            Toast.makeText(this, "Enter a valid time", Toast.LENGTH_SHORT).show();
            return;
        }

        timeLeftMillis = minutes * 60 * 1000;

        countDownTimer = new CountDownTimer(timeLeftMillis, 1000) {

            @Override
            public void onTick(long millisUntilFinished) {
                timeLeftMillis = millisUntilFinished;
                updateTimerText();
            }

            @Override
            public void onFinish() {
                timerRunning = false;
                tvTimer.setText("Time's Up!");
            }
        }.start();

        timerRunning = true;
    }

    private void resetTimer() {
        if (countDownTimer != null) {
            countDownTimer.cancel();
        }
        timerRunning = false;
        timeLeftMillis = 0;
        updateTimerText();
        etMinutes.setText("");
    }

    private void updateTimerText() {
        int minutes = (int) (timeLeftMillis / 1000) / 60;
        int seconds = (int) (timeLeftMillis / 1000) % 60;

        String timeFormatted = String.format(Locale.getDefault(),
                "%02d:%02d", minutes, seconds);

        tvTimer.setText(timeFormatted);
    }

    @Override
    protected void onPause() {
        super.onPause();
        if (countDownTimer != null) {
            countDownTimer.cancel();
        }
        timerRunning = false;
    }
}

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4. strings.xml

<resources>
    <string name="app_name">CountdownTimerApp</string>
    <string name="student_name">Student Name: FirstName LastName</string>
</resources>

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5. AndroidManifest.xml (Check Entry)

<application
    android:allowBackup="true"
    android:supportsRtl="true"
    android:theme="@style/Theme.CountdownTimerApp">

    <activity android:name=".MainActivity">
        <intent-filter>
            <action android:name="android.intent.action.MAIN"/>
            <category android:name="android.intent.category.LAUNCHER"/>
        </intent-filter>
    </activity>

</application>

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6. Expected Output