How can I validate EditText input in Android?

This example demonstrate about How can I validate EditText input 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.java
<? 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"
   android :layout_margin= "16dp"
   tools :context= ".MainActivity" >
   <EditText
      android :id= "@+id/editText"
      android :layout_width= "match_parent"
      android :layout_height= "wrap_content"
      android :hint= "Enter alpha-numeric text"
      android :inputType= "text"
      tools :ignore= "Autofill" />
</RelativeLayout>
Step 3 − Add the following code to src/ValidateFilter.java
package app.tutorialspoint.com.sample ;
import android.text.InputFilter ;
import android.text.Spanned ;
import android.util.Log ;
import java.util.regex.Matcher ;
import java.util.regex.Pattern ;
public class ValidateFilter implements InputFilter {
   @Override
   public CharSequence filter (CharSequence source , int start , int end , Spanned dest ,
   int dstart , int dend) {
      for ( int i = start ; i < end ; i++) {
         String checkMe = String. valueOf (source.charAt(i)) ;
         Pattern pattern =
         Pattern. compile ( "[ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz123456789_]*" ) ;
         Matcher matcher = pattern.matcher(checkMe) ;
         boolean valid = matcher.matches() ;
         if (!valid) {
            Log. d ( "" , "invalid" ) ;
            return "" ;
         }
      }
      return null;
   }
}
Step 4 − Add the following code to src/MainActivity.java
package app.tutorialspoint.com.sample ;
import android.os.Bundle ;
import android.support.v7.app.AppCompatActivity ;
import android.text.InputFilter ;
import android.widget.EditText ;
public class MainActivity extends AppCompatActivity {
   @Override
   protected void onCreate (Bundle savedInstanceState) {
      super .onCreate(savedInstanceState) ;
      setContentView(R.layout. activity_main ) ;
      EditText editText = findViewById(R.id. editText ) ;
      editText.setFilters( new InputFilter[]{ new ValidateFilter()}) ;
   }
}
Step 5 − 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.tutorialspoint.com.sample" >
   <uses-permission android :name= "android.permission.CALL_PHONE" />
   <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 –