Null pointer Exception

[athirasanthosh]

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.qslll.expandingpager/com.qslll.expandingpager.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v4.view.ViewPager.setAdapter(android.support.v4.view.PagerAdapter)' on a null object reference at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2339) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2413) at android.app.ActivityThread.access$800(ActivityThread.java:155) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1317) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:135) at android.app.ActivityThread.main(ActivityThread.java:5343) at java.lang.reflect.Method.invoke(Native Method) at java.lang.reflect.Method.invoke(Method.java:372) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:905) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:700) Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v4.view.ViewPager.setAdapter(android.support.v4.view.PagerAdapter)' on a null object reference at com.qslll.expandingpager.MainActivity.onCreate(MainActivity.java:42) at android.app.Activity.performCreate(Activity.java:6010) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1129) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2292) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2413)  at android.app.ActivityThread.access$800(ActivityThread.java:155)  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1317)  at android.os.Handler.dispatchMessage(Handler.java:102)  at android.os.Looper.loop(Looper.java:135)  at android.app.ActivityThread.main(ActivityThread.java:5343)  at java.lang.reflect.Method.invoke(Native Method)  at java.lang.reflect.Method.invoke(Method.java:372)  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:905)  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:700) 

[qs-lll]

maybe viewPager be null :)