java.lang.InstantiationException: can't instantiate class Activity

[Issue]

07-28 20:57:29.342    2159-2159/com.victor.travelassistant E/AndroidRuntime﹕ FATAL EXCEPTION: main

    Process: com.victor.travelassistant, PID: 2159

    java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.victor.travelassistant/com.victor.travelassistant.MainActivity}: java.lang.InstantiationException: can't instantiate class com.victor.travelassistant.MainActivity

            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2129)

            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2253)

            at android.app.ActivityThread.access$800(ActivityThread.java:142)

            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1203)

            at android.os.Handler.dispatchMessage(Handler.java:102)

            at android.os.Looper.loop(Looper.java:136)

            at android.app.ActivityThread.main(ActivityThread.java:5120)

            at java.lang.reflect.Method.invokeNative(Native Method)

            at java.lang.reflect.Method.invoke(Method.java:515)

            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:792)

            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:608)

            at dalvik.system.NativeStart.main(Native Method)

     Caused by: java.lang.InstantiationException: can't instantiate class com.victor.travelassistant.MainActivity

            at java.lang.Class.newInstanceImpl(Native Method)

            at java.lang.Class.newInstance(Class.java:1208)

            at android.app.Instrumentation.newActivity(Instrumentation.java:1061)

            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2120)

            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2253)

            at android.app.ActivityThread.access$800(ActivityThread.java:142)

            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1203)

            at android.os.Handler.dispatchMessage(Handler.java:102)

            at android.os.Looper.loop(Looper.java:136)

            at android.app.ActivityThread.main(ActivityThread.java:5120)

            at java.lang.reflect.Method.invokeNative(Native Method)

            at java.lang.reflect.Method.invoke(Method.java:515)

            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:792)

            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:608)

            at dalvik.system.NativeStart.main(Native Method)

[Solution]

Problem    : 
abstract public class MainActivity extends ActionBarActivity implements FragmentDrawer.FragmentDrawerListener{

Solution   : 
public class MainActivity extends ActionBarActivity implements FragmentDrawer.FragmentDrawerListener{