How to change a textView Style at runtime in android?

This example demonstrates how do I change a textView style in runtime in android.
Step 1 − Create a new project in Android Studio, go to File ⇒ New Project and fill all required details to create a new project.
Step 2 − Add the following code to res/layout/activity_main.xml.
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
   xmlns:tools="http://schemas.android.com/tools"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   tools:context=".MainActivity">
   <TextView
      android:id="@+id/textView"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="Have a nice day!"
      android:textSize="36sp"
      android:layout_centerInParent="true"/>
</RelativeLayout>
Step 3 – Add the following code in res/values/styles.xml
<resources>
<style name="boldText">
   <item name="android:textStyle">bold|italic</item>
   <item name="android:textColor">#FFFFFF</item>
</style>
<style name="normalText">
   <item name="android:textStyle">normal</item>
   <item name="android:textColor">#C0C0C0</item>
</style>
</resources
Step 4 – Add the following code in res/values/strings.xml
<resources>
   <string name="app_name">Sample</string>
   <color name="highlightedTextViewColor">#000088</color>
   <color name="normalTextViewColor">#000044</color>
</resources>
Step 5 − Add the following code to src/MainActivity.java
import android.os.Build;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;
public class MainActivity extends AppCompatActivity {
   TextView textView;
   @Override
   protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
      textView = findViewById(R.id.textView);
      textView.setOnClickListener(new View.OnClickListener() {
         @Override
         public void onClick(View v) {
            if (Build.VERSION.SDK_INT < 23) {
               textView.setTextAppearance(getApplicationContext(), R.style.boldText);
            } else {
               textView.setTextAppearance(R.style.boldText);
            }
            textView.setBackgroundResource(R.color.highlightedTextViewColor);
         }
      });
   }
}
Step 6 – Add the following code to androidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android" package="app.com.sample">
   <application
      android:allowBackup="true"
      android:icon="@mipmap/ic_launcher"
      android:label="@string/app_name"
      android:roundIcon="@mipmap/ic_launcher_round"
      android:supportsRtl="true"
      android:theme="@style/AppTheme">
      <activity android:name=".MainActivity">
         <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
         </intent-filter>
      </activity>
   </application>
</manifest>
Let's try to run your application. I assume you have connected your actual Android Mobile device with your computer. To run the app from android studio, open one of your project's activity files and click Run  icon from the toolbar. Select your mobile device as an option and then check your mobile device which will display your default screen –
Click here to download the project code.