ActionBarTab导航：java.lang.NullPointerException

Android Studio告诉我，我的21行有问题。你能帮我吗

import android.app.ActionBar;
import android.app.FragmentTransaction;
import android.support.v4.app.FragmentActivity;
//import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;


public class MainActivity extends FragmentActivity implements ActionBar.TabListener{

    ActionBar actionBar;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        actionBar = getActionBar();
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
        actionBar.addTab(actionBar.newTab().setText("Today").setTabListener(this));
        actionBar.addTab(actionBar.newTab().setText("Tomorrow").setTabListener(this));
    }

<there is imported tabselection actions. i haven`t got place>

}

---

请添加您的日志，看起来getActionBar返回空值，我也这么认为。但我不知道该怎么处理谢谢你们，伙计们！我自己修好的。

01-31 19:09:13.121  14719-14719/com.example.root.myapplication I/Process﹕ Sending signal. PID: 14719 SIG: 9
01-31 19:14:12.589  14795-14795/com.example.root.myapplication D/AndroidRuntime﹕ Shutting down VM
01-31 19:14:12.589  14795-14795/com.example.root.myapplication W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0xa4cc1b20)
01-31 19:14:12.589  14795-14795/com.example.root.myapplication E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.example.root.myapplication, PID: 14795
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.root.myapplication/com.example.root.myapplication.MainActivity}: java.lang.NullPointerException
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2184)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2233)
            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:5001)
            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:785)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at com.example.root.myapplication.MainActivity.onCreate(MainActivity.java:21)
            at android.app.Activity.performCreate(Activity.java:5231)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2148)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2233)
            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:5001)
            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:785)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
            at dalvik.system.NativeStart.main(Native Method)