creating Tabbec Activity in eclipse (targeted version sdk 21)

Question

I dont know what could be the reason; but whenever i'm trying to create a tabbed activity in eclipse (following tutorial)it gives this error

:java.lang.RuntimeException: Unable to start activity ComponentInfo{mypackage} java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setNavigationMode(int)' on a null object reference" Blockquote

If i download the source code; it runs.But, if i try to use downloaded activity in my existing android project( by adding classes,XML and declaring new activity in manifest), it gives same error.

How to solve this problem? I badly need to implement tabbed activity as my second activity! Code of TabbedActivity

package info.androidhive.tabsswipe;

import com.mity.medicalinformationbd.R;

import info.androidhive.tabsswipe.adapter.TabsPagerAdapter;

import android.annotation.SuppressLint;

import android.app.ActionBar;

import android.app.ActionBar.Tab;

import android.app.FragmentTransaction;

import android.os.Bundle;

import android.support.v4.app.FragmentActivity;

import android.support.v4.view.ViewPager;

import android.view.Window;

@SuppressWarnings("deprecation")
@SuppressLint("NewApi") public class SecondActivity extends FragmentActivity implements
    ActionBar.TabListener {
private ViewPager viewPager;
private TabsPagerAdapter mAdapter;
private ActionBar actionBar;
// Tab titles
private String[] tabs = { "Top Rated", "Games", "Movies" };
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    requestWindowFeature(Window.FEATURE_ACTION_BAR);
    setContentView(R.layout.tab_main);
    // Initilization
    viewPager = (ViewPager) findViewById(R.id.pager);
    actionBar = getActionBar();
    mAdapter = new TabsPagerAdapter(getSupportFragmentManager());

    viewPager.setAdapter(mAdapter);
    //actionBar.setHomeButtonEnabled(false);
    actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);        

    // Adding Tabs
    for (String tab_name : tabs) {
        actionBar.addTab(actionBar.newTab().setText(tab_name)
                .setTabListener(this));
    }

    /**
     * on swiping the viewpager make respective tab selected
     * */

    viewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {

        @Override
        public void onPageSelected(int position) {
            // on changing the page
            // make respected tab selected
            actionBar.setSelectedNavigationItem(position);
        }

        @Override
        public void onPageScrolled(int arg0, float arg1, int arg2) {
        }

        @Override
        public void onPageScrollStateChanged(int arg0) {
        }
    });
}

@Override
public void onTabReselected(Tab tab, FragmentTransaction ft) {
}
@Override
public void onTabSelected(Tab tab, FragmentTransaction ft) {
    // on tab selected
    // show respected fragment view
    viewPager.setCurrentItem(tab.getPosition());
}

@Override
public void onTabUnselected(Tab tab, FragmentTransaction ft) {
}}

MainActivity Segment

        public void onItemClick(AdapterView<?> parent, View arg1, int pos, long id) {
                RelativeLayout rl = (RelativeLayout) arg1;
                TextView tv = (TextView) rl.getChildAt(0);
                myAutoComplete.setText(tv.getText().toString());
                Intent intent = new Intent(MainActivity.this, SecondActivity.class);
                 startActivity(intent);
            }