How to turn on Flash light programmatically in android?

This example demonstrates how do I turn on Flash light programatically in android.
Step 1 − Create a new project in Android Studio, go to File ⇒ New Project and fill all required details to create a new project.
Step 2 − Add the following code to res/layout/activity_main.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:gravity="center"
   android:orientation="vertical">

   <ToggleButton
      android:id="@+id/onOffFlashlight"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:textOn="Turn Off"
      android:textOff="Turn On"
      android:checked="false"
      android:text="Turn On/Off Camera LED/ Flashlight Android" />
</LinearLayout>
Step 3 − Add the following code to src/MainActivity.java
import android.content.Context;
import android.content.DialogInterface;
import android.content.pm.PackageManager;
import android.hardware.camera2.CameraAccessException;
import android.hardware.camera2.CameraManager;
import android.os.Bundle;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.widget.CompoundButton;
import android.widget.ToggleButton;

public class MainActivity extends AppCompatActivity {

   private CameraManager mCameraManager;
   private String mCameraId;
   private ToggleButton toggleButton;

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

      boolean isFlashAvailable = getApplicationContext().getPackageManager()
         .hasSystemFeature(PackageManager.FEATURE_CAMERA_FRONT);

      if (!isFlashAvailable) {
         showNoFlashError();
      }

      mCameraManager = (CameraManager) getSystemService(Context.CAMERA_SERVICE);
      try {
         mCameraId = mCameraManager.getCameraIdList()[0];
      } catch (CameraAccessException e) {
         e.printStackTrace();
      }

      toggleButton = findViewById(R.id.onOffFlashlight);
      toggleButton.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
         @Override
         public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
            switchFlashLight(isChecked);
         }
      });
   }

   public void showNoFlashError() {
      AlertDialog alert = new AlertDialog.Builder(this)
      .create();
      alert.setTitle("Oops!");
      alert.setMessage("Flash not available in this device...");
      alert.setButton(DialogInterface.BUTTON_POSITIVE, "OK", new DialogInterface.OnClickListener() {
         public void onClick(DialogInterface dialog, int which) {
            finish();
         }
      });
      alert.show();
   }

   public void switchFlashLight(boolean status) {
      try {
         mCameraManager.setTorchMode(mCameraId, status);
      } catch (CameraAccessException e) {
         e.printStackTrace();
      }
   }
}
Step 4 - Add the following code to androidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
   package="app.com.sample">

   <uses-permission android:name="android.permission.CAMERA" />
   <uses-feature android:name="android.hardware.camera.flash" />

   <application
      android:allowBackup="true"
      android:icon="@mipmap/ic_launcher"
      android:label="@string/app_name"
      android:roundIcon="@mipmap/ic_launcher_round"
      android:supportsRtl="true"
      android:theme="@style/AppTheme">
      <activity android:name=".MainActivity">
         <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
         </intent-filter>
      </activity>
   </application>
</manifest>
Let's try to run your application. I assume you have connected your actual Android Mobile device with your computer. To run the app from android studio, open one of your project's activity files and click Run  Icon from the toolbar. Select your mobile device as an option and then check your mobile device which will display your default screen –