mainActivity.java

import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;
import androidx.lifecycle.ViewModelProvider;
import android.os.Bundle;
import android.view.View;

public class MainActivity extends AppCompatActivity implements View.OnClickListener{
    private ViewModelPractice viewModelPractice;

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

        viewModelPractice = new ViewModelProvider(this).get(ViewModelPractice.class);

        Fragment fg = new FragmentPractice();

        FragmentManager fragmentManager = getSupportFragmentManager();

        fragmentManager.beginTransaction().add(R.id.fragment_container,fg).commit();

    }


    @Override
    public void onClick(View v) {
        switch (v.getId()){
            case R.id.change_value_button :
                viewModelPractice.setValueOfLiveData(viewModelPractice.getValue()+1);
        }
    }
}