title: Android Studio : Class Not Found
body: <p>I am building a chat app using Firebase. When I want to test my app this error shows and the app crashes. The error is:</p>
  
  <pre><code>09-26 17:27:38.437 29482-29482/shashoug.com.zoolisd E/AndroidRuntime: FATAL EXCEPTION: main
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2309)
        at android.app.ActivityThread.access$700(ActivityThread.java:157)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1289)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:176)
        at android.app.ActivityThread.main(ActivityThread.java:5317)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:511)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1102)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:869)
        at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.ClassNotFoundException: Didn't find class "shashoug.com.zoolisd.MainActivity" on path: /data/app/shashoug.com.zoolisd-2.apk
        at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:65)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:501)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:461)
        at android.app.Instrumentation.newActivity(Instrumentation.java:1071)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2171)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2309) 
        at android.app.ActivityThread.access$700(ActivityThread.java:157) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1289) 
        at android.os.Handler.dispatchMessage(Handler.java:99) 
        at android.os.Looper.loop(Looper.java:176) 
        at android.app.ActivityThread.main(ActivityThread.java:5317) 
        at java.lang.reflect.Method.invokeNative(Native Method) 
        at java.lang.reflect.Method.invoke(Method.java:511) 
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1102) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:869) 
        at dalvik.system.NativeStart.main(Native Method) 
  09-26 17:27:40.079 29482-29482/? I/Process: Sending signal. PID: 29482 SIG: 9
  </code></pre>