Android remplacer un fragment

fragment.java

Fragment frag;

//ajout d'un fragment 

	TonFragment newFragment = new TonFragment();
        android.support.v4.app.FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
        transaction.add(R.id.fragment_container, newFragment).addToBackStack("A_B_TAG");
        transaction.commit();
        
//remplacement d'un fragment

	frag = new AutreFragment();
        android.support.v4.app.FragmentManager fm = getSupportFragmentManager();
        android.support.v4.app.FragmentTransaction fragmentTransaction = fm.beginTransaction();
        fragmentTransaction.replace(R.id.fragment_container, frag);
        fragmentTransaction.setTransition(fragmentTransaction.TRANSIT_FRAGMENT_OPEN);
        fragmentTransaction.commit();
        
        
// Utuiliser le back button 


    @Override
    public void onBackPressed() {
        if (getSupportFragmentManager().findFragmentByTag("FragmentC") != null) {

            getSupportFragmentManager().popBackStack("A_B_TAG",
                    fm.POP_BACK_STACK_INCLUSIVE);
        } else {
            super.onBackPressed();
        }
    }