BackStack in Fragments:-

Create Interface class:

public interface OnBackListner {
    void back();
}

In Activity:

public class HomeActivity extends AppCompatActivity{

    OnBackListner onBackListner;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_navigationdrawer);
    }

    @Override
    public void onBackPressed() {
            if (onBackListner != null) {
                onBackListner.back();
            } else {
                finish();
            }       
    }

    public void setOnBackPressedListener(OnBackListner onBackPressedListener) {
        this.onBackListner = onBackPressedListener;
    }

}

In 1st Fragment :

((HomeActivity) getActivity()).setOnBackPressedListener(new OnBackListner() {
            @Override
            public void back() {
                //startActivity(new Intent(getActivity(), MainActivity.class));
                CommonUtils.hideKeyboard(getActivity());
                getActivity().finish();
            }

        });

2nd Fragment:

((HomeActivity) getActivity()).setOnBackPressedListener(new OnBackListner() {
            @Override
            public void back() {
                //startActivity(new Intent(getActivity(), MainActivity.class));
                CommonUtils.hideKeyboard(getActivity());
                getActivity().getSupportFragmentManager().popBackStackImmediate();
            }

        });