Android- ViewModel and Live Data

Android-ViewModel-LiveData.java

package mohammad.samandari.testviewmodel;

import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;
import androidx.lifecycle.Observer;
import androidx.lifecycle.ViewModelProvider;

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    private static final String TAG = "Lord";
    private MyViewModel myViewModel;

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

        Button button = findViewById(R.id.button);
        final TextView textView = findViewById(R.id.textView);

        // Get the ViewModel.
        myViewModel = new ViewModelProvider(this).get(MyViewModel.class);

        // Create the observer which updates the UI.
        final Observer<Integer> aObserver = new Observer<Integer>() {
            @Override
            public void onChanged (@Nullable final Integer a) {
                // Update the UI, in this case, a TextView.
                textView.setText(String.valueOf(a));
            }
        };

        // Observe the LiveData, passing in this activity as the LifecycleOwner and the observer.
        myViewModel.getA().observe(this, aObserver);

        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick (View v) {
                myViewModel.getA().setValue(myViewModel.getA().getValue() + 1);

            }
        });
    }
}

MyViewModel.java

package mohammad.samandari.testviewmodel;
import androidx.lifecycle.MutableLiveData;
import androidx.lifecycle.ViewModel;

public class MyViewModel extends ViewModel {

    private MutableLiveData<Integer> a;

    public MutableLiveData<Integer> getA () {
        if (a == null) {
            a = new MutableLiveData<Integer>();
            a.setValue(0);
        }
        return a;
    }
}