总是出现这个空指针异常

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.study.myapplication/com.study.myapplication.MainActivity}: java.lang.NullPointerException

            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)

            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)

            at android.app.ActivityThread.access$800(ActivityThread.java:135)

            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)

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

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

            at android.app.ActivityThread.main(ActivityThread.java:5017)

            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:779)

            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)

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

     Caused by: java.lang.NullPointerException

            at com.study.myapplication.MainActivity.Getdata(MainActivity.java:44)

            at com.study.myapplication.MainActivity.onCreate(MainActivity.java:30)

            at android.app.Activity.performCreate(Activity.java:5231)

            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)

            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)

            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)

            at android.app.ActivityThread.access$800(ActivityThread.java:135)

            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)

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

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

            at android.app.ActivityThread.main(ActivityThread.java:5017)

            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:779)

            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)

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

求解。