Bluetooth is a very useful functionality to send or receive files between two or more devices. There are several Bluetooth APIs to perform various operations of Bluetooth that include:

• Scanning of a new Bluetooth device
• The Pairing of two devices
• Getting a list of all paired devices

In Android, BluetoothAdapter class is used to implement Bluetooth. The example below demonstrates BluetoothAdapter class to control Bluetooth-related operations:

After creating an application in Android Studio under package com.firstapp.ashulakhwan.greatlearning, you need to modify some files in your project. These files include MainActivity.java, activity_main.xml, and AndroidManifest.xml. The contents of these files after modification are as follows:
MainActivity.java

package com.firstapp.ashulakhwan.greatlearning;

import android.app.Activity;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;

import android.content.Intent;
import android.os.Bundle;
import android.view.View;

import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ListView;

import android.widget.Toast;
import java.util.ArrayList;
import java.util.Set;

public class MainActivity extends Activity  {
   Button btn1,btn2,btn3,btn4;
   private BluetoothAdapter BTAdapter;
   private Set<BluetoothDevice>pairedDevices;
   ListView lstvw;

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

      btn1 = (Button) findViewById(R.id.button);
      btn2 =(Button)findViewById(R.id.button2);
      btn3 =(Button)findViewById(R.id.button3);
      btn4 =(Button)findViewById(R.id.button4);

      BTAdapter = BluetoothAdapter.getDefaultAdapter();
      lstvw = (ListView)findViewById(R.id.listView);
   }

   public void on(View v){
      if (!BA.isEnabled()) {
         Intent btON = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
         startActivityForResult(btON, 0);
         Toast.makeText(getApplicationContext(), "Bluetooth is turned on",Toast.LENGTH_LONG).show();
      } else {
         Toast.makeText(getApplicationContext(), "Bluetooth is already turned on", Toast.LENGTH_LONG).show();
      }
   }

   public void off(View v){
      BA.disable();
      Toast.makeText(getApplicationContext(), "Bluetooth is turned off" ,Toast.LENGTH_LONG).show();
   }

    
   public  void visible(View v){
      Intent getVisible = new Intent(BluetoothAdapter.ACTION_REQUEST_DISCOVERABLE);
      startActivityForResult(getVisible, 0);
   }

    
   public void list(View v){
      pairedDevices = BA.getBondedDevices();
        
      ArrayList list = new ArrayList();

      for(BluetoothDevice bt : pairedDevices) list.add(bt.getName());
      Toast.makeText(getApplicationContext(), "The list of Paired Devices", Toast.LENGTH_SHORT).show();

      final ArrayAdapter adapter = new  ArrayAdapter(this,android.R.layout.simple_list_item_1, list);
        
      lstvw.setAdapter(adapter);
   }
}

activity_main.xml file will look like this:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 
xmlns:android="http://schemas.android.com/apk/res/android"
   xmlns:tools="http://schemas.android.com/tools" 
   android:layout_width="match_parent"
   android:layout_height="match_parent" 
   android:paddingLeft="@dimen/activity_horizontal_margin"
   android:paddingRight="@dimen/activity_horizontal_margin"
   android:paddingTop="@dimen/activity_vertical_margin"
   android:paddingBottom="@dimen/activity_vertical_margin"
   tools:context=".MainActivity"
   android:transitionGroup="true">
   
   <TextView android:text="Android Bluetooth" 
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:id="@+id/textview"
      android:textSize="38dp"
      android:layout_alignParentTop="true"
      android:layout_centerHorizontal="true" />
      
   <TextView
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="Great Learning"
      android:id="@+id/textView"
      android:layout_below="@+id/textview"
      android:layout_centerHorizontal="true"
      android:textColor="#bd65f0"
      android:textSize="40dp" />
      
   <ImageView
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:id="@+id/imageView"
      android:layout_below="@+id/textView"
      android:layout_centerHorizontal="true"
      android:theme="@style/Base.TextAppearance.AppCompat" />
      
   <Button
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="Turn On BT"
      android:id="@+id/button"
      android:layout_below="@+id/imageView"
      android:layout_toStartOf="@+id/imageView"
      android:layout_toLeftOf="@+id/imageView"
      android:clickable="true"
      android:onClick="on" />
      
   <Button
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="Make device visible"
      android:onClick="visible"
      android:id="@+id/button2"
      android:layout_alignBottom="@+id/button"
      android:layout_centerHorizontal="true" />
      
   <Button
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="List of paired devices"
      android:onClick="list"
      android:id="@+id/button3"
      android:layout_below="@+id/imageView"
      android:layout_toRightOf="@+id/imageView"
      android:layout_toEndOf="@+id/imageView" />
      
   <Button
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="Turn OFF BT"
      android:onClick="off"
      android:id="@+id/button4"
      android:layout_below="@+id/button"
      android:layout_alignParentLeft="true"
      android:layout_alignParentStart="true" />
      
   <ListView
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:id="@+id/listView"
      android:layout_alignParentBottom="true"
      android:layout_alignLeft="@+id/button"
      android:layout_alignStart="@+id/button"
      android:layout_below="@+id/textView2" />
      
   <TextView
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="List of Paired devices:"
      android:id="@+id/textView2"
      android:textColor="#ff34ff06"
      android:textSize="25dp"
      android:layout_below="@+id/button4"
      android:layout_alignLeft="@+id/listView"
      android:layout_alignStart="@+id/listView" />

</RelativeLayout>

The following content is for the file AndroidManifest.xml:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
   package="com.firstapp.ashulakhwan.greatlearning" >
   <uses-permission android:name="android.permission.BLUETOOTH"/>
   <uses-permission android:name="android.permission.BLUETOOTH_ADMIN"/>
   
   <application
      android:allowBackup="true"
      android:icon="@mipmap/ic_launcher"
      android:label="@string/app_name"
      android:theme="@style/CustomTheme" >
      
      <activity
         android:name=".MainActivity"
         android:label="@string/app_name" >
         
         <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
         </intent-filter>
         
      </activity>
      
   </application>
</manifest>

Now, all the modifications of the files are done and you can try running the application on Android Emulator or device to check the results. 

Android - Camera
The Camera is a very useful functionality to capture images. In Android, you can add this functionality to your application by using MediaStore.ACTION_IMAGE_CAPTURE. To understand its working, you can refer to the example shown below:

The first thing you need to do is to create an application under a package com.firstapp.ashulakhwan.greatlearning

The next step is to modify its main file which can be found as src/MainActivity.java. Refer to the following code snippet for this file:

package com.firstapp.ashulakhwan.greatlearning;

import android.Manifest;
import android.app.Activity;
import android.app.AlertDialog;

import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.content.SharedPreferences;
import android.content.pm.PackageManager;

import android.net.Uri;
import android.os.Bundle;
import android.provider.Settings;

import android.support.v4.app.ActivityCompat;
import android.support.v4.content.ContextCompat;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;

public class MainActivity extends AppCompatActivity {
   public static final int MY_PERMISSIONS_REQUEST_CAMERA = 100;
   public static final String ALLOW_KEY = "Camera_Allowed";
   public static final String CAMERA_PREF = "Camera_Preference";

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

      if (ContextCompat.checkSelfPermission(this, Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED) {
         if (getFromPref(this, ALLOW_KEY)) {
            showSettingsAlert();
         } else if (ContextCompat.checkSelfPermission(this,
            Manifest.permission.CAMERA)
            
            != PackageManager.PERMISSION_GRANTED) {
               
               if (ActivityCompat.shouldShowRequestPermissionRationale(this,
                  Manifest.permission.CAMERA)) {
                  showAlert();
               } else {
                  ActivityCompat.requestPermissions(this,
                     new String[]{Manifest.permission.CAMERA},
                     MY_PERMISSIONS_REQUEST_CAMERA);
               }
            }
      } else {
         openCamera();
      }
      
   }
   public static void saveToPreferences(Context context, String key, Boolean allowed) {
      SharedPreferences myPrefs = context.getSharedPreferences(CAMERA_PREF, 
         Context.MODE_PRIVATE);
      SharedPreferences.Editor prefsEditor = myPrefs.edit();
      prefsEditor.putBoolean(key, allowed);
      prefsEditor.commit();
   }
      
   public static Boolean getFromPref(Context context, String key) {
      SharedPreferences myPrefs = context.getSharedPreferences(CAMERA_PREF, 
         Context.MODE_PRIVATE);
      return (myPrefs.getBoolean(key, false));
   }
      
   private void showAlert() {
      AlertDialog alertDialog = new AlertDialog.Builder(MainActivity.this).create();
      alertDialog.setTitle("Alert");
      alertDialog.setMessage("The application requires permission access.");
      
      alertDialog.setButton(AlertDialog.BUTTON_NEGATIVE, "Not allowed",
         new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int which) {
               dialog.dismiss();
               finish();
            }
      });
         
      alertDialog.setButton(AlertDialog.BUTTON_POSITIVE, "ALLOW",
         new DialogInterface.OnClickListener() {
         
            public void onClick(DialogInterface dialog, int which) {
               dialog.dismiss();
               ActivityCompat.requestPermissions(MainActivity.this,
               new String[]{Manifest.permission.CAMERA},
               MY_PERMISSIONS_REQUEST_CAMERA);
            }
      });
      alertDialog.show();
   }
      
   private void showSettingsAlert() {
      AlertDialog alertDialog = new AlertDialog.Builder(MainActivity.this).create();
      alertDialog.setTitle("Alert");
      alertDialog.setMessage("The application requires permission access.");
      alertDialog.setButton(AlertDialog.BUTTON_NEGATIVE, "Permission Denied",
         new DialogInterface.OnClickListener() {
         
            public void onClick(DialogInterface dialog, int which) {
               dialog.dismiss();
            }
      });
         
      alertDialog.setButton(AlertDialog.BUTTON_POSITIVE, "SETTINGS",
         new DialogInterface.OnClickListener() {
                    
            public void onClick(DialogInterface dialog, int which) {
               dialog.dismiss();
               startInstalledAppDetailsActivity(MainActivity.this);
            }
      });
         
      alertDialog.show();
   }
      
   @Override
   public void onRequestPermissionsResult(int requestCode, String permissions[], int[] grantResults) {
      switch (requestCode) {
         case MY_PERMISSIONS_REQUEST_CAMERA: {
            for (int i = 0, len = permissions.length; i < len; i++) {
               String permission = permissions[i];
            
               if (grantResults[i] == PackageManager.PERMISSION_DENIED) {
                  boolean 
                  showRationale = 
                     ActivityCompat.shouldShowRequestPermissionRationale(
                     this, permission);
                  
                  if (showRationale) {
                     showAlert();
                  } else if (!showRationale) {
             
                     saveToPreferences(MainActivity.this, ALLOW_KEY, true);
                  }
               }
            }
         }         
      }
   }
      
   @Override
   protected void onResume() {
      super.onResume();
   }
      
   public static void startInstalledAppDetailsActivity(final Activity context) {
      if (context == null) {
         return;
      }
         
      final Intent i = new Intent();
      i.setAction(Settings.ACTION_APPLICATION_DETAILS_SETTINGS);
      i.addCategory(Intent.CATEGORY_DEFAULT);
      i.setData(Uri.parse("Package:" + context.getPackageName()));
      i.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
      i.addFlags(Intent.FLAG_ACTIVITY_NO_HISTORY);
      i.addFlags(Intent.FLAG_ACTIVITY_EXCLUDE_FROM_RECENTS);
      context.startActivity(i);
   }
      
   private void openCamera() {
      Intent intent = new Intent("android.media.action.IMAGE_CAPTURE");
      startActivity(intent);
   }
}

After that, you might need to modify its layout XML file with the name res/layout/activity_main.xml. The content for the files is shown below:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
   xmlns:tools="http://schemas.android.com/tools"
   android:layout_width="match_parent"
   android:layout_height="match_parent" 
   android:paddingLeft="@dimen/activity_horizontal_margin"
   android:paddingRight="@dimen/activity_horizontal_margin"
   android:paddingTop="@dimen/activity_vertical_margin"
   android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">
</RelativeLayout>

Next, you will be required to modify the AndroidManifest.xml file:
 

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
   package="com.firstapp.ashulakhwan.greatlearning" >
  <uses-permission android:name="android.permission.CAMERA" />
   <application
      android:allowBackup="true"
      android:icon="@drawable/ic_launcher"
      android:label="@string/app_name"
      android:theme="@style/CustomTheme" >
      <activity
         android:name="com.firstapp.ashulakhwan.greatlearning"
         android:label="@string/app_name" >
         <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
         </intent-filter>
     </activity>
   </application>
</manifest>

In the last step, you need to add permission for the Camera to use on your device and then run the application to verify the results.