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Android App Development Coding Questions

Create a button that changes the background color of a TextView when clicked.

java

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Button button = findViewById(R.id.button);
TextView textView = findViewById(R.id.text_view);
button.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        textView.setBackgroundColor(Color.RED);
    }
});

Write a function that calculates the factorial of a given integer.

java

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public int factorial(int n) {
    if (n == 0) {
        return 1;
    } else {
        return n * factorial(n - 1);
    }
}

Implement a custom ListView that displays a list of items with an image and text.

java

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public class CustomListAdapter extends ArrayAdapter<String> {
    private final Activity context;
    private final String[] itemNames;
    private final Integer[] itemImages;

    public CustomListAdapter(Activity context, String[] itemNames, Integer[] itemImages) {
        super(context, R.layout.custom_list_item, itemNames);
        this.context = context;
        this.itemNames = itemNames;
        this.itemImages = itemImages;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        LayoutInflater inflater = context.getLayoutInflater();
        View rowView = inflater.inflate(R.layout.custom_list_item, null, true);
        TextView itemNameView = rowView.findViewById(R.id.item_name);
        ImageView itemImageView = rowView.findViewById(R.id.item_image);
        itemNameView.setText(itemNames[position]);
        itemImageView.setImageResource(itemImages[position]);
        return rowView;
    }
}

Create a function that takes a string as input and returns the reverse of the string.

java

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public String reverseString(String input) {
    String output = "";
    for (int i = input.length() - 1; i >= 0; i--) {
        output += input.charAt(i);
    }
    return output;
}

Implement a custom AlertDialog that displays a message and two buttons.

java

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AlertDialog.Builder builder = new AlertDialog.Builder(this);
builder.setMessage("Are you sure you want to delete this item?");
builder.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
    @Override
    public void onClick(DialogInterface dialog, int which) {
        // Delete the item
    }
});
builder.setNegativeButton("No", null);
AlertDialog dialog = builder.create();
dialog.show();

Create a function that calculates the sum of two integers.

java

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public int sum(int a, int b) {
    return a + b;
}

Implement a custom ArrayAdapter that displays a list of items with a checkbox and text.

java

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public class CustomArrayAdapter extends ArrayAdapter<String> {
    private final Context context;
    private final String[] items;

    public CustomArrayAdapter(Context context, String[] items) {
        super(context, R.layout.custom_list_item, items);
        this.context = context;
        this.items = items;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        View rowView = inflater.inflate(R.layout.custom_list_item, parent, false);
        CheckBox checkBox = rowView.findViewById(R.id.checkbox);
        TextView textView = rowView.findViewById(R.id.text);
        textView.setText(items[position]);
        return rowView;
    }
}

Create a function that calculates the area of a circle given its radius.

java

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public double areaOfCircle(double radius) {
    return Math.PI * radius * radius;
}

Create a function that checks if a string is a palindrome.

java

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public boolean isPalindrome(String input) {
    String reversed = "";
    for (int i = input.length() - 1; i >= 0; i--) {
        reversed += input.charAt(i);
    }
    return input.equals(reversed);
}

Implement a custom ViewPager that displays a list of images.

java

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public class CustomPagerAdapter extends PagerAdapter {
    private Context context;
    private int[] images;

    public CustomPagerAdapter(Context context, int[] images) {
        this.context = context;
        this.images = images;
    }

    @Override
    public int getCount() {
        return images.length;
    }

    @Override
    public boolean isViewFromObject(View view, Object object) {
        return view == object;
    }

    @Override
    public Object instantiateItem(ViewGroup container, int position) {
        ImageView imageView = new ImageView(context);
        imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
        imageView.setImageResource(images[position]);
        container.addView(imageView);
        return imageView;
    }

    @Override
    public void destroyItem(ViewGroup container, int position, Object object) {
        container.removeView((ImageView) object);
    }
}

Create a function that sorts an array of integers in ascending order.

java

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public void sortArray(int[] array) {
    Arrays.sort(array);
}

Implement a custom ProgressBar that displays a progress bar with a text label.

xml

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<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content">

    <TextView
        android:id="@+id/progress_text"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true" />

    <ProgressBar
        android:id="@+id/progress_bar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@id/progress_text"
        android:indeterminate="false" />

</RelativeLayout>

java

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public class CustomProgressBar extends RelativeLayout {
    private ProgressBar progressBar;
    private TextView progressText;

    public CustomProgressBar(Context context) {
        super(context);
        init(context);
    }

    public CustomProgressBar(Context context, AttributeSet attrs) {
        super(context, attrs);
        init(context);
    }

    private void init(Context context) {
        LayoutInflater inflater = LayoutInflater.from(context);
        inflater.inflate(R.layout.custom_progress_bar, this, true);
        progressBar = findViewById(R.id.progress_bar);
        progressText = findViewById(R.id.progress_text);
    }

    public void setProgress(int progress) {
        progressBar.setProgress(progress);
        progressText.setText(progress + "%");
    }
}

Create a function that checks if a number is a prime number.

java

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public boolean isPrime(int n) {
    if (n <= 1) {
        return false;
    }
    for (int i = 2; i <= Math.sqrt(n); i++) {
        if (n % i == 0) {
            return false;
        }
    }
    return true;
}

Create a function that calculates the factorial of a number.

java

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public int factorial(int n) {
    if (n == 0) {
        return 1;
    }
    int result = 1;
    for (int i = 1; i <= n; i++) {
        result *= i;
    }
    return result;
}

Implement a custom ListView that displays a list of items with an image and text.

java

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public class CustomListAdapter extends BaseAdapter {
    private Context context;
    private List<Item> items;

    public CustomListAdapter(Context context, List<Item> items) {
        this.context = context;
        this.items = items;
    }

    @Override
    public int getCount() {
        return items.size();
    }

    @Override
    public Object getItem(int position) {
        return items.get(position);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        if (convertView == null) {
            convertView = LayoutInflater.from(context).inflate(R.layout.custom_list_item, parent, false);
        }

        ImageView imageView = convertView.findViewById(R.id.item_image);
        TextView textView = convertView.findViewById(R.id.item_text);

        Item item = items.get(position);
        imageView.setImageResource(item.getImage());
        textView.setText(item.getText());

        return convertView;
    }
}

Create a function that calculates the Fibonacci sequence up to a given number of terms.

java

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public int[] fibonacci(int n) {
    int[] result = new int[n];
    result[0] = 0;
    if (n > 1) {
        result[1] = 1;
        for (int i = 2; i < n; i++) {
            result[i] = result[i - 1] + result[i - 2];
        }
    }
    return result;
}

Implement a custom dialog that displays a message and two buttons.

java

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public class CustomDialog extends Dialog {
    private TextView messageTextView;
    private Button positiveButton;
    private Button negativeButton;

    public CustomDialog(Context context) {
        super(context);
        init(context);
    }

    public CustomDialog(Context context, int themeResId) {
        super(context, themeResId);
        init(context);
    }

    private void init(Context context) {
        setContentView(R.layout.custom_dialog);
        messageTextView = findViewById(R.id.message_text);
        positiveButton = findViewById(R.id.positive_button);
        negativeButton = findViewById(R.id.negative_button);
    }

    public void setMessage(String message) {
        messageTextView.setText(message);
    }

    public void setPositiveButton(String text, View.OnClickListener listener) {
        positiveButton.setText(text);
        positiveButton.setOnClickListener(listener);
    }

    public void setNegativeButton(String text, View.OnClickListener listener) {
        negativeButton.setText(text);
        negativeButton.setOnClickListener(listener);
    }
}

Create a function that calculates the sum of an array of integers.

java

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public int sumArray(int[] array) {
    int sum = 0;
    for (int i = 0; i < array.length; i++) {
        sum += array[i];
    }
    return sum;
}

Create a function that returns the largest element in an array of integers.

java

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public int findMax(int[] arr) {
    int max = arr[0];
    for (int i = 1; i < arr.length; i++) {
        if (arr[i] > max) {
            max = arr[i];
        }
    }
    return max;
}

Implement a custom View that displays a circle with a given color and radius.

java

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public class CircleView extends View {
    private Paint paint;
    private int color;
    private int radius;

    public CircleView(Context context) {
        super(context);
        init();
    }

    public CircleView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    private void init() {
        paint = new Paint();
        paint.setAntiAlias(true);
    }

    public void setColor(int color) {
        this.color = color;
        paint.setColor(color);
        invalidate();
    }

    public void setRadius(int radius) {
        this.radius = radius;
        invalidate();
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvas.drawCircle(getWidth() / 2, getHeight() / 2, radius, paint);
    }
}

Create a function that reverses a string.

java

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public String reverseString(String str) {
    StringBuilder sb = new StringBuilder(str);
    return sb.reverse().toString();
}

Implement a custom AlertDialog that displays a message and a single button.

java

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public class CustomAlertDialog extends AlertDialog {
    private TextView messageTextView;
    private Button positiveButton;

    public CustomAlertDialog(Context context) {
        super(context);
        init(context);
    }

    public CustomAlertDialog(Context context, int themeResId) {
        super(context, themeResId);
        init(context);
    }

    private void init(Context context) {
        setView(R.layout.custom_alert_dialog);
        messageTextView = findViewById(R.id.message_text);
        positiveButton = findViewById(R.id.positive_button);
    }

    public void setMessage(String message) {
        messageTextView.setText(message);
    }

    public void setPositiveButton(String text, View.OnClickListener listener) {
        positiveButton.setText(text);
        positiveButton.setOnClickListener(listener);
    }
}

Create a function that checks whether a string is a palindrome.

java

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public boolean isPalindrome(String str) {
    String reversed = new StringBuilder(str).reverse().toString();
    return str.equals(reversed);
}

Implement a custom ProgressBar that displays a progress value and a label.

java

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public class CustomProgressBar extends ProgressBar {
    private TextView labelTextView;

    public CustomProgressBar(Context context) {
        super(context);
        init();
    }

    public CustomProgressBar(Context context, AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    private void init() {
        LayoutInflater inflater = LayoutInflater.from(getContext());
        View view = inflater.inflate(R.layout.custom_progress_bar, this, true);
        labelTextView = view.findViewById(R.id.label_text);
    }

    public void setLabel(String label) {
        labelTextView.setText(label);
    }
}

Write a program to display a list of items in a RecyclerView with a custom layout for each item.
Answer:

kotlin

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class Item(val name: String, val description: String)

class ItemAdapter(val items: List<Item>) : RecyclerView.Adapter<ItemAdapter.ViewHolder>() {

    class ViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
        val nameTextView: TextView = itemView.findViewById(R.id.nameTextView)
        val descriptionTextView: TextView = itemView.findViewById(R.id.descriptionTextView)
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
        val view = LayoutInflater.from(parent.context).inflate(R.layout.item_layout, parent, false)
        return ViewHolder(view)
    }

    override fun onBindViewHolder(holder: ViewHolder, position: Int) {
        val item = items[position]
        holder.nameTextView.text = item.name
        holder.descriptionTextView.text = item.description
    }

    override fun getItemCount() = items.size
}

Write a program to display a list of images in a RecyclerView with a grid layout.
Answer:

kotlin

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class ImageAdapter(val images: List<Int>) : RecyclerView.Adapter<ImageAdapter.ViewHolder>() {

    class ViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
        val imageView: ImageView = itemView.findViewById(R.id.imageView)
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
        val view = LayoutInflater.from(parent.context).inflate(R.layout.image_layout, parent, false)
        return ViewHolder(view)
    }

    override fun onBindViewHolder(holder: ViewHolder, position: Int) {
        val image = images[position]
        holder.imageView.setImageResource(image)
    }

    override fun getItemCount() = images.size
}

Write a program to download an image from the internet and display it in an ImageView.
Answer:

kotlin

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val imageView = findViewById<ImageView>(R.id.imageView)

val url = "https://example.com/image.jpg"

val task = object : AsyncTask<String, Void, Bitmap>() {
    override fun doInBackground(vararg urls: String): Bitmap {
        val url = URL(urls[0])
        val connection = url.openConnection() as HttpURLConnection
        connection.doInput = true
        connection.connect()
        val input = connection.inputStream
        return BitmapFactory.decodeStream(input)
    }

    override fun onPostExecute(result: Bitmap) {
        imageView.setImageBitmap(result)
    }
}

task.execute(url)

Write a program to play a sound file when a button is clicked.
Answer:

kotlin

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val mediaPlayer = MediaPlayer.create(this, R.raw.sound_file)

val button = findViewById<Button>(R.id.button)
button.setOnClickListener {
    mediaPlayer.start()
}

Write a program to display a dialog box with a message and an OK button.
Answer:

kotlin

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val builder = AlertDialog.Builder(this)
builder.setMessage("Hello, world!")
builder.setPositiveButton("OK") { _, _ ->
    // do nothing
}
builder.show()

Write a program to display a Snackbar with an action button that prints a message to the console when clicked.
Answer:

kotlin

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val coordinatorLayout = findViewById<CoordinatorLayout>(R.id.coordinatorLayout)

val snackbar = Snackbar.make(coordinatorLayout, "Hello, world!", Snackbar.LENGTH_LONG)
snackbar.setAction("ACTION") {
    Log.d("TAG", "Action clicked")
}
snackbar.show()

Write a program to launch an activity when a button is clicked.
Answer:

kotlin

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val intent = Intent(this, OtherActivity::class.java)
startActivity(intent)

Write a Java program to calculate the sum of all even numbers from 1 to 100.

csharp

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public class EvenSum {
    public static void main(String[] args) {
        int sum = 0;
        for (int i = 2; i <= 100; i += 2) {
            sum += i;
        }
        System.out.println("Sum of even numbers from 1 to 100: " + sum);
    }
}

Write a program to check if a given string is a palindrome or not.

java

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import java.util.Scanner;

public class Palindrome {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter a string: ");
        String str = sc.nextLine();
        sc.close();
        int len = str.length();
        boolean palindrome = true;
        for (int i = 0; i < len / 2; i++) {
            if (str.charAt(i) != str.charAt(len - i - 1)) {
                palindrome = false;
                break;
            }
        }
        if (palindrome) {
            System.out.println(str + " is a palindrome");
        } else {
            System.out.println(str + " is not a palindrome");
        }
    }
}

Write a program to calculate the factorial of a given number.

java

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import java.util.Scanner;

public class Factorial {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter a number: ");
        int n = sc.nextInt();
        sc.close();
        int fact = 1;
        for (int i = 2; i <= n; i++) {
            fact *= i;
        }
        System.out.println(n + "! = " + fact);
    }
}

Write a program to find the largest and smallest numbers in a given array.

python

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public class ArrayMinMax {
    public static void main(String[] args) {
        int[] arr = {5, 3, 8, 2, 9, 1};
        int min = arr[0];
        int max = arr[0];
        for (int i = 1; i < arr.length; i++) {
            if (arr[i] < min) {
                min = arr[i];
            }
            if (arr[i] > max) {
                max = arr[i];
            }
        }
        System.out.println("Minimum number: " + min);
        System.out.println("Maximum number: " + max);
    }
}

Write a program to count the number of occurrences of a given element in a given array.

csharp

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public class ArrayCount {
    public static void main(String[] args) {
        int[] arr = {2, 3, 4, 3, 5, 3};
        int key = 3;
        int count = 0;
        for (int i = 0; i < arr.length; i++) {
            if (arr[i] == key) {
                count++;
            }
        }
        System.out.println(key + " occurs " + count + " times in the array");
    }
}

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Introduction to Android app development

Installing Android Studio

Creating The First Android app

Android app lifecycle

Building User interface with layouts and widgets

Handling user input with event listeners

Activities and Intents

Persisting data with shared preferences and SQLite databases

Networking and web services in Android

Using external libraries and APIs

Integrating Google Maps into your Android app

Adding multimedia features like audio and video playback

Working with notifications and background services

Debugging and testing your Android app

Publishing your app to the Google Play Store

Developing Android games with Unity or other game engines

Implementing in-app purchases and advertisements

Building a responsive UI with ConstraintLayout

Integrating Firebase services into the Android app

Securing your app with permissions and encryption.

Android App Development Interview Questions

Android App Development Interview Questions-2

Android App Development Coding Questions

Android App Development Coding Questions