Hi
I have referred to your 'Android App Development for Beginners - 13 - Create an Interface with Java' tutorial.
I have installed Android 6.0 SDK on Android Studio.
There is an error that is occurring whether I run the code on my device in debugging mode or on my emulator.

I have attached the error from logcat.
Kindly help me out on this problem.


11-27 23:33:01.128 4455-4455/? I/art: Not late-enabling -Xcheck:jni (already on)
11-27 23:33:01.129 4455-4455/? I/art: Late-enabling JIT
11-27 23:33:02.470 4455-4455/? I/art: JIT created with code_cache_capacity=2MB compile_threshold=1000
11-27 23:33:04.760 4455-4455/com.neilcastellino.tutorial_13 W/System: ClassLoader referenced unknown path: /data/app/com.neilcastellino.tutorial_13-1/lib/arm
11-27 23:33:05.645 4455-4462/com.neilcastellino.tutorial_13 W/art: Suspending all threads took: 20.283ms
11-27 23:33:06.101 4455-4462/com.neilcastellino.tutorial_13 W/art: Suspending all threads took: 11.131ms
11-27 23:33:06.449 4455-4455/com.neilcastellino.tutorial_13 D/AndroidRuntime: Shutting down VM
11-27 23:33:06.505 4455-4455/com.neilcastellino.tutorial_13 E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.neilcastellino.tutorial_13, PID: 4455
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.neilcastellino.tutorial_13/com.neilcastellino.tutorial_13.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.CharSequence android.support.v7.widget.Toolbar.getTitle()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.CharSequence android.support.v7.widget.Toolbar.getTitle()' on a null object reference
at android.support.v7.widget.ToolbarWidgetWrapper.(ToolbarWidgetWrapper.java:98)
at android.support.v7.widget.ToolbarWidgetWrapper.(ToolbarWidgetWrapper.java:91)
at android.support.v7.app.ToolbarActionBar.(ToolbarActionBar.java:73)
at android.support.v7.app.AppCompatDelegateImplV7.setSupportActionBar(AppCompatDelegateImplV7.java:205)
at android.support.v7.app.AppCompatActivity.setSupportActionBar(AppCompatActivity.java:99)
at com.neilcastellino.tutorial_13.MainActivity.onCreate(MainActivity.java:23)
at android.app.Activity.performCreate(Activity.java:6237)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
at android.app.ActivityThread.-wrap11(ActivityThread.java) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:148) 
at android.app.ActivityThread.main(ActivityThread.java:5417) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 
11-27 23:33:16.692 4455-4462/com.neilcastellino.tutorial_13 W/art: Suspending all threads took: 27.849ms
11-27 23:33:18.358 4455-4455/com.neilcastellino.tutorial_13 I/Process: Sending signal. PID: 4455 SIG: 9