title: Android room shows the error AppDatabase_Impl does not exist
body: <p>I am developing an app and add the room for database but it shows the error is </p>
  
  <blockquote>
    <p>java.lang.RuntimeException: Unable to start activity
    ComponentInfo{com.app.android/com.app.android.activities.AttendanceActivity}:
    java.lang.RuntimeException: cannot find implementation for
    com.app.android.db.AppDatabase. AppDatabase_Impl does not exist</p>
  </blockquote>
  
  <p>In gradle file I have add every thing. My gradle file is shown below. I don't know. what is the problem. This code is working in another application. But it shows in this application. Kindly help me.</p>
  
  <pre><code>apply plugin: 'com.android.application'
  apply plugin: 'realm-android'
  android {
  useLibrary 'org.apache.http.legacy'
  compileSdkVersion 25
  buildToolsVersion '26.0.2'
  defaultConfig {
      applicationId 'com.app.android'
      minSdkVersion 14
      targetSdkVersion 25
      versionCode 16
  //     edumia   versionCode 16
      versionName "2.0.5"
  //       edumia  versionName "2.0.5"
      testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
  }
  buildTypes {
      debug {
          debuggable true
      }
      release {
          minifyEnabled true
          proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
      }
  }
  productFlavors {
  }
  }
  repositories {
  jcenter()
  maven {
      url 'https://github.com/uPhyca/stetho-realm/raw/master/maven-repo'
  }
  maven {
      url 'https://dl.bintray.com/ayz4sci/maven/'
  }
  
  }
  
  allprojects {
  repositories {
      jcenter()
      maven {
          url "https://maven.google.com"
      }
  }
  }
  
  dependencies {
  implementation 'com.android.support.constraint:constraint-layout:1.0.2'
  compile fileTree(include: ['*.jar'], dir: 'libs')
  
  
  compile group: 'org.apache.httpcomponents', name: 'httpclient-android', version: '4.3.5.1'
  
  compile 'com.android.support:appcompat-v7:21.0.+'
  compile 'com.google.code.gson:gson:2.6.2'
  compile 'com.squareup.retrofit2:retrofit:2.1.0'
  compile 'com.squareup.retrofit2:converter-gson:2.1.0'
  compile 'com.squareup.okhttp3:logging-interceptor:3.3.1'
  compile 'com.facebook.shimmer:shimmer:0.1.0@aar'
  compile 'com.afollestad.material-dialogs:core:0.9.3.0'
  compile 'com.afollestad.material-dialogs:commons:0.9.3.0'
  compile 'com.facebook.stetho:stetho:1.4.1'
  compile 'com.uphyca:stetho_realm:2.0.0'
  compile 'com.evernote:android-job:1.1.11'
  compile 'com.firebase:firebase-jobdispatcher:0.6.0'
  compile 'com.android.support:design:25.0.0'
  compile 'com.ss.bannerslider:bannerslider:1.6.1'
  compile 'com.android.support:recyclerview-v7:23.1.1'
  compile 'com.android.support:cardview-v7:23.1.1'
  compile 'com.ayz4sci.androidfactory:downloadprogress:1.0.2'
  compile('com.alibaba.android:ultraviewpager:1.0.6@aar') {
      transitive = true
  }
  
  
  compile 'android.arch.lifecycle:extensions:1.0.0-rc1';
  compile 'android.arch.persistence.room:runtime:1.0.0-rc1';
  annotationProcessor 'android.arch.lifecycle:compiler:1.0.0-rc1';
  annotationProcessor 'android.arch.persistence.room:compiler:1.0.0-rc1';
  }
  </code></pre>
  
  <p><strong>MainActivity.java</strong></p>
  
  <pre><code>public class AttendanceActivity extends ActionBarActivity {
      private Class_ class_;
      private AppDatabase database;
  
              @Override
              protected void onCreate(Bundle savedInstanceState) {
              super.onCreate(savedInstanceState);
              setContentView(R.layout.activity_main);
  
              database = AppDatabase.getDatabase(getApplicationContext());
              database.classDao().removeAllUsers();
  
              Class_ aClass = new Class_(1,"model");
              database.classDao().addClass(aClass);
  
              Log.d(TAG, "added success");
  
  }
  </code></pre>
  
  <p><strong>AppDatabase.java</strong></p>
  
  <pre><code>public abstract class AppDatabase extends RoomDatabase{
  
  private static AppDatabase INSTANCE;
  public abstract ClassDao classDao();
  public static AppDatabase getDatabase(Context context) {
      if (INSTANCE == null) {
         INSTANCE =
                  Room.databaseBuilder(context, AppDatabase.class, "edumiadatabase")
  //Room.inMemoryDatabaseBuilder(context.getApplicationContext(), AppDatabase.class)
                          // To simplify the exercise, allow queries on the main thread.
                          // Don't do this on a real app!
                          .allowMainThreadQueries()
                          // recreate the database if necessary
                          .fallbackToDestructiveMigration()
                          .build();
  
  
      }
      return INSTANCE;
  }
  
  public static void destroyInstance() {
      INSTANCE = null;
  }
  }
  </code></pre>
  
  <p><strong>Class_.java</strong></p>
  
  <pre><code>public class Class_ {
  @PrimaryKey
  public int id;
  public String Class_;
  
  
  public int getId() {
      return id;
  }
  
  public void setId(int id) {
      this.id = id;
  }
  
  public String getClass_() {
      return Class_;
  }
  
  public void setClass_(String class_) {
      Class_ = class_;
  }
  
  public Class_(int id, String class_){
      this.id=id;
      this.Class_ = class_;
  }
  }
  </code></pre>
  
  <p><strong>ClassDao.java</strong></p>
  
  <pre><code>@Dao
  public interface ClassDao {
  
      @Insert(onConflict = OnConflictStrategy.REPLACE)
      void addClass(Class_ user);
  
      @Query("delete from user")
      void removeAllUsers();
  
  }
  </code></pre>