getActionBar().setTitle(); Java.lang.NullPoint异常解决方案，是由于低版本不支持直接获取的缘故，修改方案：
try changing your theme to this <style name="AppTheme" parent="android:Theme.Holo.Light.DarkActionBar"> and not the AppCompat Version
另外一种情况，如果是低版本，API低于11的解决方案：
It basically depends on whch api you are targeting.If it less than 14 use
<style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
and in your activity call your actionbar using this getSupportActionBar().setDisplayHomeAsUpEnabled(true);