Where and how to use to static variables in android studio?

This example demonstrates about how and where do I use static variable in android studio.

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"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
   xmlns:app="http://schemas.android.com/apk/res-auto"
   xmlns:tools="http://schemas.android.com/tools"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   tools:context="MainActivity">
   <TextView
      android:id="@+id/Question"
      android:layout_width="wrap_content"
      android:layout_height="93dp"
      android:padding="8dp"
      android:text="I'm a Static Variable"
      android:layout_marginTop="32sp"
      android:layout_marginLeft="8dp"
      android:textSize="32dp"
      tools:layout_editor_absoluteY="8dp" />
</LinearLayout>

Step 3 − Add the following code to src/MainActivity.java

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
public class MainActivity extends AppCompatActivity {
   public static final String TAG = "I'm a Static Variable";
   @Override
   protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
   }
   protected void onStart() {
      super.onStart();
      Log.i(TAG, "onStart");
   }
   protected void onPause() {
      super.onPause();
      Log.i(TAG, "onPause");
   }
   protected void onStop() {
      super.onStop();
      Log.i(TAG, "onStop");
   }
}

Step 4 − 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.