10-01 08:09:16.690: I/dalvikvm-heap(2115): Grow heap (frag case) to 6.026MB for 2536932-byte allocation
10-01 08:09:17.180: W/dalvikvm(2115): threadid=1: thread exiting with uncaught exception (group=0xb0d1ab20)
10-01 08:09:17.240: E/AndroidRuntime(2115): FATAL EXCEPTION: main
10-01 08:09:17.240: E/AndroidRuntime(2115): Process: com.example.jizhang, PID: 2115
10-01 08:09:17.240: E/AndroidRuntime(2115): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.jizhang/com.jaskey.jizhang.MainActivity}: java.lang.ClassCastException: android.widget.LinearLayout cannot be cast to android.support.v4.view.ViewPager
10-01 08:09:17.240: E/AndroidRuntime(2115):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
10-01 08:09:17.240: E/AndroidRuntime(2115):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
10-01 08:09:17.240: E/AndroidRuntime(2115):     at android.app.ActivityThread.access$800(ActivityThread.java:135)
10-01 08:09:17.240: E/AndroidRuntime(2115):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
10-01 08:09:17.240: E/AndroidRuntime(2115):     at android.os.Handler.dispatchMessage(Handler.java:102)
10-01 08:09:17.240: E/AndroidRuntime(2115):     at android.os.Looper.loop(Looper.java:136)
10-01 08:09:17.240: E/AndroidRuntime(2115):     at android.app.ActivityThread.main(ActivityThread.java:5017)
10-01 08:09:17.240: E/AndroidRuntime(2115):     at java.lang.reflect.Method.invokeNative(Native Method)
10-01 08:09:17.240: E/AndroidRuntime(2115):     at java.lang.reflect.Method.invoke(Method.java:515)
10-01 08:09:17.240: E/AndroidRuntime(2115):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
10-01 08:09:17.240: E/AndroidRuntime(2115):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
10-01 08:09:17.240: E/AndroidRuntime(2115):     at dalvik.system.NativeStart.main(Native Method)
10-01 08:09:17.240: E/AndroidRuntime(2115): Caused by: java.lang.ClassCastException: android.widget.LinearLayout cannot be cast to android.support.v4.view.ViewPager
10-01 08:09:17.240: E/AndroidRuntime(2115):     at com.jaskey.jizhang.MainActivity.onCreate(MainActivity.java:30)
10-01 08:09:17.240: E/AndroidRuntime(2115):     at android.app.Activity.performCreate(Activity.java:5231)
10-01 08:09:17.240: E/AndroidRuntime(2115):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
10-01 08:09:17.240: E/AndroidRuntime(2115):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
10-01 08:09:17.240: E/AndroidRuntime(2115):     ... 11 more

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        mPager=(ViewPager) findViewById(R.id.pager);//here where the error is thrown
        mPageAdpater=new MainPageAdpater(getSupportFragmentManager());
        mPager.setAdapter(mPageAdpater);

<android.support.v4.view.ViewPager
        android:id="@+id/pager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        />
</LinearLayout>