This is the demo code to maintain the same data after changing orientation of application in Android. (This contains 2 sample code one onSaveInstanceState and another is using ViewModel)

DemoActivity.java

package com.suresh.androidpractice.orientationchange;

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

import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;
import androidx.lifecycle.ViewModelProviders;

import com.suresh.androidpractice.R;

public class DemoActivity extends AppCompatActivity {

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

        TextView textViewDemo = findViewById(R.id.text_common);
        textViewDemo.setVisibility(View.VISIBLE);

        DemoActivityViewModel model = ViewModelProviders.of(this).get(DemoActivityViewModel.class);
//        DemoActivityViewModel model = new DemoActivityViewModel();
        String myRandomNumber = model.getUUID();
        textViewDemo.setText(myRandomNumber);
    }
}

DemoActivityViewModel.java

package com.suresh.androidpractice.orientationchange;

import androidx.lifecycle.ViewModel;

import java.util.UUID;

public class DemoActivityViewModel extends ViewModel {
    private String myRandomNumber;

    public String getUUID() {
        if (myRandomNumber == null) {
            myRandomNumber = "Generated Id: " + UUID.randomUUID().toString().replace("-", "");
        }
        return myRandomNumber;
    }

    @Override
    protected void onCleared() {
        super.onCleared();
    }
}

MainActivity.java

package com.suresh.androidpractice.orientationchange;

import android.content.res.Configuration;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;

import com.suresh.androidpractice.R;

import java.util.UUID;

public class MainActivity extends AppCompatActivity {
    private String randomUUID = "";
    private static final String KEY_UUID = "UUID";
    private static final String TAG = "orientation_demo";

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

        TextView textViewDemo = findViewById(R.id.text_common);
        textViewDemo.setVisibility(View.VISIBLE);

        textViewDemo.setText("Orientation change demo");
        randomUUID = (savedInstanceState == null) ? getUUID() : savedInstanceState.getString(KEY_UUID);
        textViewDemo.setText(randomUUID);

        Log.e(TAG, "OnCreate: randomUUID: " + randomUUID);
    }

    @Override
    public void onConfigurationChanged(@NonNull Configuration newConfig) {
        super.onConfigurationChanged(newConfig);
        Log.e(TAG, "onConfigurationChanged() called with: newConfig = [" + newConfig + "]");
    }

    @Override
    protected void onSaveInstanceState(@NonNull Bundle outState) {
        super.onSaveInstanceState(outState);
        Log.e(TAG, "onSaveInstanceState() called with: outState = [" + outState + "]");
        outState.putString(KEY_UUID, randomUUID);
        Log.e(TAG, "Random UUID saved");
    }

    @Override
    protected void onRestoreInstanceState(@NonNull Bundle savedInstanceState) {
        super.onRestoreInstanceState(savedInstanceState);
        Log.e(TAG, "onRestoreInstanceState() called with: savedInstanceState = [" + savedInstanceState + "]");
        Log.e(TAG, "Restored Random UUID: " + savedInstanceState.getString(KEY_UUID));
    }

    private String getUUID() {
        return "Generated Id: " + UUID.randomUUID().toString().replace("-", "");
    }
}