Q-4: Attempt the following (Any two) (10 Marks)

Questions

A: Describe the Android architecture in detail.
B: Develop a simple calculator using table layout.
C: Write java file for event handling of Checkbox in android application.

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Answer A: Android Architecture in Detail

Android architecture is based on Linux kernel and consists of multiple layers. Here's the detailed architecture:

Android Architecture Layers (Bottom to Top):

┌─────────────────────────────────────────────────┐
│            Applications Layer                   │
│  (Phone, SMS, Calendar, Maps, Browser, etc.)    │
├─────────────────────────────────────────────────┤
│         Application Framework Layer             │
│  (Activity Manager, Content Providers, etc.)    │
├─────────────────────────────────────────────────┤
│              Libraries Layer                    │ Android Runtime
│     (Media, Graphics, SQLite, etc.)             │ (Core Libraries + DVM)
├─────────────────────────────────────────────────┤
│              Linux Kernel                       │
│   (Drivers, Memory Management, Security)        │
└─────────────────────────────────────────────────┘

1. Linux Kernel Layer (Bottom Layer)

• Foundation: Android is built on Linux kernel (version 2.6)
• Functions:
  • Memory management
  • Process management
  • Security model
  • Hardware abstraction
  • Device drivers (Display, Camera, Bluetooth, Audio, etc.)
  • Power management

2. Libraries Layer

Native Libraries (C/C++):

• Media Libraries: For audio/video playback and recording
• Surface Manager: Manages access to display subsystem
• LibWebCore: Web browser engine (WebKit)
• SGL (Scalable Graphics Library): 2D graphics engine
• 3D Libraries: OpenGL ES for 3D graphics
• FreeType: Font rendering
• SQLite: Lightweight database engine
• SSL: Secure Socket Layer for internet security

3. Android Runtime

• Core Libraries: Provide functionality of Java programming language
• Dalvik Virtual Machine (DVM):
  • Register-based virtual machine
  • Optimized for mobile devices
  • Runs .dex (Dalvik Executable) files
  • Multiple instances can run simultaneously

4. Application Framework Layer

Key Components:

• Activity Manager: Manages activity lifecycle
• Content Providers: Manages data sharing between applications
• Resource Manager: Manages non-code resources (strings, graphics)
• Notification Manager: Manages notifications
• Location Manager: Provides location services
• Package Manager: Manages application packages
• Telephony Manager: Manages telephony services
• Window Manager: Manages windows and screens

5. Applications Layer (Top Layer)

• Pre-installed Apps: Phone, SMS, Calendar, Maps, Browser
• Third-party Apps: Downloaded from Play Store
• User Apps: Custom developed applications

Architecture Benefits:

1. Reusability: Applications can reuse components
2. Security: Each layer provides security
3. Flexibility: Easy to develop and deploy applications
4. Open Source: Customizable and extensible

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Answer B: Simple Calculator using Table Layout

XML Layout File (activity_calculator.xml):

<?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:padding="16dp">

    <!-- Display Screen -->
    <EditText
        android:id="@+id/editTextDisplay"
        android:layout_width="match_parent"
        android:layout_height="80dp"
        android:textSize="24sp"
        android:gravity="right|center_vertical"
        android:background="@android:color/white"
        android:textColor="@android:color/black"
        android:layout_marginBottom="16dp"
        android:inputType="none"
        android:focusable="false" />

    <!-- Calculator Buttons using TableLayout -->
    <TableLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:stretchColumns="0,1,2,3">

        <!-- Row 1: Clear, +/-, %, ÷ -->
        <TableRow android:layout_marginBottom="8dp">
            <Button android:id="@+id/btnClear" android:text="C" 
                android:layout_margin="4dp" android:textSize="20sp"/>
            <Button android:id="@+id/btnPlusMinus" android:text="+/-" 
                android:layout_margin="4dp" android:textSize="20sp"/>
            <Button android:id="@+id/btnPercent" android:text="%" 
                android:layout_margin="4dp" android:textSize="20sp"/>
            <Button android:id="@+id/btnDivide" android:text="÷" 
                android:layout_margin="4dp" android:textSize="20sp"/>
        </TableRow>

        <!-- Row 2: 7, 8, 9, × -->
        <TableRow android:layout_marginBottom="8dp">
            <Button android:id="@+id/btn7" android:text="7" 
                android:layout_margin="4dp" android:textSize="20sp"/>
            <Button android:id="@+id/btn8" android:text="8" 
                android:layout_margin="4dp" android:textSize="20sp"/>
            <Button android:id="@+id/btn9" android:text="9" 
                android:layout_margin="4dp" android:textSize="20sp"/>
            <Button android:id="@+id/btnMultiply" android:text="×" 
                android:layout_margin="4dp" android:textSize="20sp"/>
        </TableRow>

        <!-- Row 3: 4, 5, 6, - -->
        <TableRow android:layout_marginBottom="8dp">
            <Button android:id="@+id/btn4" android:text="4" 
                android:layout_margin="4dp" android:textSize="20sp"/>
            <Button android:id="@+id/btn5" android:text="5" 
                android:layout_margin="4dp" android:textSize="20sp"/>
            <Button android:id="@+id/btn6" android:text="6" 
                android:layout_margin="4dp" android:textSize="20sp"/>
            <Button android:id="@+id/btnSubtract" android:text="-" 
                android:layout_margin="4dp" android:textSize="20sp"/>
        </TableRow>

        <!-- Row 4: 1, 2, 3, + -->
        <TableRow android:layout_marginBottom="8dp">
            <Button android:id="@+id/btn1" android:text="1" 
                android:layout_margin="4dp" android:textSize="20sp"/>
            <Button android:id="@+id/btn2" android:text="2" 
                android:layout_margin="4dp" android:textSize="20sp"/>
            <Button android:id="@+id/btn3" android:text="3" 
                android:layout_margin="4dp" android:textSize="20sp"/>
            <Button android:id="@+id/btnAdd" android:text="+" 
                android:layout_margin="4dp" android:textSize="20sp"/>
        </TableRow>

        <!-- Row 5: 0 (spans 2 columns), ., = -->
        <TableRow>
            <Button android:id="@+id/btn0" android:text="0" 
                android:layout_margin="4dp" android:textSize="20sp"
                android:layout_span="2"/>
            <Button android:id="@+id/btnDecimal" android:text="." 
                android:layout_margin="4dp" android:textSize="20sp"/>
            <Button android:id="@+id/btnEquals" android:text="=" 
                android:layout_margin="4dp" android:textSize="20sp"/>
        </TableRow>

    </TableLayout>

</LinearLayout>

Java Activity File (CalculatorActivity.java):

public class CalculatorActivity extends AppCompatActivity {
    
    private EditText display;
    private String currentNumber = "";
    private String operator = "";
    private double firstNumber = 0;
    private boolean isNewOperation = true;
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_calculator);
        
        display = findViewById(R.id.editTextDisplay);
        setupButtons();
    }
    
    private void setupButtons() {
        // Number buttons
        findViewById(R.id.btn0).setOnClickListener(v -> appendNumber("0"));
        findViewById(R.id.btn1).setOnClickListener(v -> appendNumber("1"));
        findViewById(R.id.btn2).setOnClickListener(v -> appendNumber("2"));
        findViewById(R.id.btn3).setOnClickListener(v -> appendNumber("3"));
        findViewById(R.id.btn4).setOnClickListener(v -> appendNumber("4"));
        findViewById(R.id.btn5).setOnClickListener(v -> appendNumber("5"));
        findViewById(R.id.btn6).setOnClickListener(v -> appendNumber("6"));
        findViewById(R.id.btn7).setOnClickListener(v -> appendNumber("7"));
        findViewById(R.id.btn8).setOnClickListener(v -> appendNumber("8"));
        findViewById(R.id.btn9).setOnClickListener(v -> appendNumber("9"));
        
        // Operator buttons
        findViewById(R.id.btnAdd).setOnClickListener(v -> setOperator("+"));
        findViewById(R.id.btnSubtract).setOnClickListener(v -> setOperator("-"));
        findViewById(R.id.btnMultiply).setOnClickListener(v -> setOperator("×"));
        findViewById(R.id.btnDivide).setOnClickListener(v -> setOperator("÷"));
        
        // Special buttons
        findViewById(R.id.btnEquals).setOnClickListener(v -> calculate());
        findViewById(R.id.btnClear).setOnClickListener(v -> clear());
        findViewById(R.id.btnDecimal).setOnClickListener(v -> appendDecimal());
    }
    
    private void appendNumber(String number) {
        if (isNewOperation) {
            currentNumber = number;
            isNewOperation = false;
        } else {
            currentNumber += number;
        }
        display.setText(currentNumber);
    }
    
    private void setOperator(String op) {
        if (!currentNumber.isEmpty()) {
            firstNumber = Double.parseDouble(currentNumber);
            operator = op;
            isNewOperation = true;
        }
    }
    
    private void calculate() {
        if (!operator.isEmpty() && !currentNumber.isEmpty()) {
            double secondNumber = Double.parseDouble(currentNumber);
            double result = 0;
            
            switch (operator) {
                case "+":
                    result = firstNumber + secondNumber;
                    break;
                case "-":
                    result = firstNumber - secondNumber;
                    break;
                case "×":
                    result = firstNumber * secondNumber;
                    break;
                case "÷":
                    if (secondNumber != 0) {
                        result = firstNumber / secondNumber;
                    } else {
                        display.setText("Error");
                        return;
                    }
                    break;
            }
            
            display.setText(String.valueOf(result));
            currentNumber = String.valueOf(result);
            operator = "";
            isNewOperation = true;
        }
    }
    
    private void clear() {
        currentNumber = "";
        operator = "";
        firstNumber = 0;
        isNewOperation = true;
        display.setText("0");
    }
    
    private void appendDecimal() {
        if (!currentNumber.contains(".")) {
            if (currentNumber.isEmpty()) {
                currentNumber = "0.";
            } else {
                currentNumber += ".";
            }
            display.setText(currentNumber);
        }
    }
}

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Answer C: Java file for Checkbox Event Handling

XML Layout File (activity_checkbox.xml):

<?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:padding="20dp">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Select your hobbies:"
        android:textSize="18sp"
        android:layout_marginBottom="20dp" />

    <CheckBox
        android:id="@+id/checkboxReading"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Reading"
        android:textSize="16sp"
        android:layout_marginBottom="10dp" />

    <CheckBox
        android:id="@+id/checkboxMusic"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Listening to Music"
        android:textSize="16sp"
        android:layout_marginBottom="10dp" />

    <CheckBox
        android:id="@+id/checkboxSports"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Playing Sports"
        android:textSize="16sp"
        android:layout_marginBottom="10dp" />

    <CheckBox
        android:id="@+id/checkboxTraveling"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Traveling"
        android:textSize="16sp"
        android:layout_marginBottom="20dp" />

    <Button
        android:id="@+id/buttonSubmit"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Submit"
        android:textSize="16sp"
        android:layout_marginBottom="20dp" />

    <TextView
        android:id="@+id/textViewResult"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Selected hobbies will appear here"
        android:textSize="16sp"
        android:background="#f0f0f0"
        android:padding="10dp" />

</LinearLayout>

Java Activity File (CheckboxActivity.java):

package com.example.checkboxdemo;

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.CheckBox;
import android.widget.CompoundButton;
import android.widget.TextView;
import android.widget.Toast;
import androidx.appcompat.app.AppCompatActivity;
import java.util.ArrayList;

public class CheckboxActivity extends AppCompatActivity {
    
    private CheckBox checkboxReading, checkboxMusic, checkboxSports, checkboxTraveling;
    private Button buttonSubmit;
    private TextView textViewResult;
    private ArrayList<String> selectedHobbies;
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_checkbox);
        
        // Initialize views
        initializeViews();
        
        // Set up event listeners
        setupEventListeners();
        
        // Initialize selected hobbies list
        selectedHobbies = new ArrayList<>();
    }
    
    private void initializeViews() {
        checkboxReading = findViewById(R.id.checkboxReading);
        checkboxMusic = findViewById(R.id.checkboxMusic);
        checkboxSports = findViewById(R.id.checkboxSports);
        checkboxTraveling = findViewById(R.id.checkboxTraveling);
        buttonSubmit = findViewById(R.id.buttonSubmit);
        textViewResult = findViewById(R.id.textViewResult);
    }
    
    private void setupEventListeners() {
        // Method 1: Using OnCheckedChangeListener for individual checkboxes
        checkboxReading.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
                handleCheckboxChange("Reading", isChecked);
            }
        });
        
        checkboxMusic.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
                handleCheckboxChange("Listening to Music", isChecked);
            }
        });
        
        checkboxSports.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
                handleCheckboxChange("Playing Sports", isChecked);
            }
        });
        
        checkboxTraveling.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
                handleCheckboxChange("Traveling", isChecked);
            }
        });
        
        // Submit button click listener
        buttonSubmit.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                displaySelectedHobbies();
            }
        });
    }
    
    // Method to handle checkbox state changes
    private void handleCheckboxChange(String hobby, boolean isChecked) {
        if (isChecked) {
            if (!selectedHobbies.contains(hobby)) {
                selectedHobbies.add(hobby);
            }
            Toast.makeText(this, hobby + " selected", Toast.LENGTH_SHORT).show();
        } else {
            selectedHobbies.remove(hobby);
            Toast.makeText(this, hobby + " deselected", Toast.LENGTH_SHORT).show();
        }
        
        // Update result text in real-time
        updateResultText();
    }
    
    // Method to update result text view
    private void updateResultText() {
        if (selectedHobbies.isEmpty()) {
            textViewResult.setText("No hobbies selected");
        } else {
            StringBuilder result = new StringBuilder("Selected Hobbies:\n");
            for (int i = 0; i < selectedHobbies.size(); i++) {
                result.append("• ").append(selectedHobbies.get(i));
                if (i < selectedHobbies.size() - 1) {
                    result.append("\n");
                }
            }
            textViewResult.setText(result.toString());
        }
    }
    
    // Method to display selected hobbies when submit is clicked
    private void displaySelectedHobbies() {
        if (selectedHobbies.isEmpty()) {
            Toast.makeText(this, "Please select at least one hobby", Toast.LENGTH_LONG).show();
            textViewResult.setText("No hobbies selected");
        } else {
            String message = "You have selected " + selectedHobbies.size() + " hobbies";
            Toast.makeText(this, message, Toast.LENGTH_LONG).show();
            
            // Display detailed results
            StringBuilder detailedResult = new StringBuilder("SUBMITTED HOBBIES:\n\n");
            for (int i = 0; i < selectedHobbies.size(); i++) {
                detailedResult.append((i + 1)).append(". ").append(selectedHobbies.get(i)).append("\n");
            }
            detailedResult.append("\nTotal: ").append(selectedHobbies.size()).append(" hobbies selected");
            textViewResult.setText(detailedResult.toString());
        }
    }
    
    // Alternative method: Using single listener for all checkboxes
    public void onCheckboxClicked(View view) {
        boolean checked = ((CheckBox) view).isChecked();
        String hobby = "";
        
        switch (view.getId()) {
            case R.id.checkboxReading:
                hobby = "Reading";
                break;
            case R.id.checkboxMusic:
                hobby = "Listening to Music";
                break;
            case R.id.checkboxSports:
                hobby = "Playing Sports";
                break;
            case R.id.checkboxTraveling:
                hobby = "Traveling";
                break;
        }
        
        handleCheckboxChange(hobby, checked);
    }
}

Key Features of this Implementation:

1. Multiple Event Handling Methods: Shows both OnCheckedChangeListener and onClick methods
2. Real-time Updates: Result updates as checkboxes are selected/deselected
3. Toast Messages: Immediate feedback for user actions
4. Validation: Checks if at least one hobby is selected
5. Dynamic Text Building: Constructs result text dynamically
6. ArrayList Management: Properly manages selected items list

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