public class MyActivity extends Activity implements View.OnClickListener {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        Button replaceBtn = (Button) findViewById(R.id.replaceFragment);
        replaceBtn.setOnClickListener(this);
    }

    @Override
    public void onClick(View view) {
        switch (view.getId()){
            case R.id.replaceFragment:
                Fragment fragment1 = new Frag1();
                FragmentTransaction fTrans = getFragmentManager().beginTransaction();
                fTrans.replace(R.id.contentFrame, fragment1);
                **fTrans.addToBackStack(null);**
                fTrans.commit();
                break;
        }
    }
}

public class Frag1 extends Fragment  implements View.OnClickListener {
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.frag1, null);
        Button replaceBtn2 = (Button) v.findViewById(R.id.replaceFragment2);
        replaceBtn2.setOnClickListener(this);
        return v;
    }

    @Override
    public void onClick(View view) {
        switch (view.getId()){
            case R.id.replaceFragment2:
                Frag2 fragment2 = new Frag2();
                FragmentTransaction fTrans = getFragmentManager().beginTransaction();
                fTrans.replace(R.id.contentFrame,fragment2);
                **fTrans.addToBackStack(null);**
                fTrans.commit();
                break;
        }
    }
}

public class Frag2 extends Fragment implements View.OnClickListener {
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.frag2, null);
        Button replaceBtn3 = (Button) v.findViewById(R.id.replaceFragment3);
        replaceBtn3.setOnClickListener(this);
        return v;
    }

    @Override
    public void onClick(View view) {
        switch (view.getId()){
            case R.id.replaceFragment3:
                Frag3 fragment3 = new Frag3();
                FragmentTransaction fTrans = getFragmentManager().beginTransaction();
                fTrans.replace(R.id.contentFrame,fragment3);
                **//do not add backstack**
                fTrans.commit();
                break;
        }
    }
}

public class Frag3 extends Fragment{
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.frag3, null);
        return v;
    }
}