cannot convert from android.app.FragmentManager to android.support.v4.app.FragmentManager

I am creating an app using Fragments for tablet.I have so far created some buttons on the left side and the fragments appear on clicking the buttons.

But i am experiencing error in my MainActivity.java file "Type mismatch error:cannot convert from android.app.FragmentManager to android.support.v4.app.FragmentManager" And that is the main reason that i cannot implement it.I have already imported android.support.v4.app.FragmentManager.

How can i resolve my problem?

My code for MainActivity.java

      import android.app.Activity;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentTransaction;
import android.view.View;
import android.widget.Button;

public class MainActivity extends Activity {
	Fragment fragment;
	Button btn1,btn2,btn3,btn4,btn5,btn6;
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		btn1=(Button)findViewById(R.id.btn1);
		btn2=(Button)findViewById(R.id.btn2);
		btn3=(Button)findViewById(R.id.btn3);
		btn4=(Button)findViewById(R.id.btn4);
		btn5=(Button)findViewById(R.id.btn5);
		btn6=(Button)findViewById(R.id.btn6);
	
		FragmentManager fm=getFragmentManager();
		FragmentTransaction ft=fm.beginTransaction();
		
		StartFragment myfragment=new StartFragment();
		ft.add(R.id.myfragment,myfragment);
		ft.commit();
		btn4.setOnClickListener(btnOnClickListener);
		btn5.setOnClickListener(btnOnClickListener);
		btn6.setOnClickListener(btnOnClickListener);
	}
		
		

		Button.OnClickListener btnOnClickListener=new Button.OnClickListener(){
			@Override
			
			public void onClick(View v)
			{
				Fragment newfragment;
				if(v==btn1)
				{
					newfragment=new Fragment1();
				}
				else if(v==btn2)
				{
					newfragment=new Fragment2();
				}
				else if(v==btn3)
				{
					newfragment=new Fragment3();
				}
				else if(v==btn4)
				{
					newfragment=new Fragment4();
				}
				else if(v==btn5)
				{
					newfragment=new Fragment5();
				}
				else if(v==btn6)
				{
					newfragment=new Fragment6();
				}
				else 
				{
					newfragment=new StartFragment();
				}
				FragmentTransaction transaction=getFragmentManager.beginTransaction();
				transaction.replace(R.id.myfragment,newfragment);
				transaction.addToBackStack(null);
				transaction.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE);
				transaction.commit();
			}
		};
		}






       

You need to use getSupportFragmentManager() in your code, not getFragmentManager() - see here for more details.

You also need to extend your class from android.support.v4.app.FragmentActivity, not just from standard android.Activity to get this method.