build.gradle

apply plugin: 'com.android.application'

android {
    compileSdkVersion 29
    buildToolsVersion "29.0.3"

    defaultConfig {
        applicationId "com.example.geofencing"
        minSdkVersion 16
        targetSdkVersion 29
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
        multiDexEnabled true
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }

}

dependencies {
    implementation 'com.android.support:multidex:1.0.3'
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation 'androidx.appcompat:appcompat:1.2.0'
    implementation 'androidx.constraintlayout:constraintlayout:2.0.4'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'androidx.test.ext:junit:1.1.2'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.3.0'
    implementation 'com.google.android.gms:play-services:12.0.1'

}

GeofenceIntentService.java

package com.example.geofencing;

import android.app.IntentService;
import android.content.Intent;
import android.widget.Toast;

import com.google.android.gms.location.Geofence;
import com.google.android.gms.location.GeofencingEvent;

public class GeofenceIntentService extends IntentService {

    public GeofenceIntentService() {
        super("GeofenceIntentService");
    }

    @Override
    protected void onHandleIntent(Intent intent) {
        GeofencingEvent geofencingEvent = GeofencingEvent.fromIntent(intent);
        if (geofencingEvent.hasError()) {
            Toast.makeText(getApplicationContext(), "Geofence error code= "
                    + geofencingEvent.getErrorCode(), Toast.LENGTH_SHORT).show();
            return;
        }
        int geofenceTransition = geofencingEvent.getGeofenceTransition();
        if (geofenceTransition == Geofence.GEOFENCE_TRANSITION_DWELL) {
            Toast.makeText(getApplicationContext(), "GEOFENCE_TRANSITION_DWELL",
                    Toast.LENGTH_SHORT).show();
        }
    }

}

MainActivity.java

package com.example.geofencing;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.app.ActivityCompat;

import android.app.PendingIntent;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.os.Bundle;
import android.widget.Toast;

import com.google.android.gms.location.Geofence;
import com.google.android.gms.location.GeofencingClient;
import com.google.android.gms.location.GeofencingRequest;
import com.google.android.gms.location.LocationServices;
import com.google.android.gms.tasks.OnFailureListener;
import com.google.android.gms.tasks.OnSuccessListener;

import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {

    private final int MINIMUM_RECOMENDED_RADIUS = 100;

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

        if (ActivityCompat.checkSelfPermission(this, android.Manifest.permission.ACCESS_FINE_LOCATION) == PackageManager.PERMISSION_GRANTED) {
            GeofencingClient geofencingClient = LocationServices.getGeofencingClient(this);
            geofencingClient.addGeofences(createGeofencingRequest(), createGeofencePendingIntent())
                    .addOnSuccessListener(this, new OnSuccessListener<Void>() {
                        @Override
                        public void onSuccess(Void aVoid) {
                            Toast.makeText(MainActivity.this, "onSuccess()", Toast.LENGTH_SHORT).show();
                        }
                    })
                    .addOnFailureListener(this, new OnFailureListener() {
                        @Override
                        public void onFailure(@NonNull Exception e) {
                            Toast.makeText(MainActivity.this,
                                    "onFailure(): " + e.getMessage(), Toast.LENGTH_SHORT).show();
                        }
                    });
        } else {
            ActivityCompat.requestPermissions(this,
                    new String[]{android.Manifest.permission.ACCESS_FINE_LOCATION}, 1);
        }
    }

    private PendingIntent createGeofencePendingIntent() {
        Intent intent = new Intent(this, GeofenceIntentService.class);
        return PendingIntent.getService(this, 0, intent, PendingIntent.FLAG_UPDATE_CURRENT);
    }

    private List createGeofenceList() {
        List<Geofence> geofenceList = new ArrayList<>();
        geofenceList.add(new Geofence.Builder()
                .setRequestId("GeofenceLocation")
                .setCircularRegion(
                        47.6062,  //Latitude
                        122.3321, //Longitude
                        MINIMUM_RECOMENDED_RADIUS)
                .setLoiteringDelay(30000)
                .setExpirationDuration(Geofence.NEVER_EXPIRE)
                .setTransitionTypes(Geofence.GEOFENCE_TRANSITION_DWELL)
                .build());
        return geofenceList;
    }

    private GeofencingRequest createGeofencingRequest() {
        GeofencingRequest.Builder builder = new GeofencingRequest.Builder();
        builder.setInitialTrigger(GeofencingRequest.INITIAL_TRIGGER_DWELL);
        builder.addGeofences(createGeofenceList());
        return builder.build();
    }

    @Override
    protected void onStop() {
        super.onStop();

        GeofencingClient geofencingClient = LocationServices.getGeofencingClient(this);
        geofencingClient.removeGeofences(createGeofencePendingIntent())
                .addOnSuccessListener(this, new OnSuccessListener<Void>() {
                    @Override
                    public void onSuccess(Void aVoid) {
                        //Success
                    }
                })
                .addOnFailureListener(this, new OnFailureListener() {
                    @Override
                    public void onFailure(@NonNull Exception e) {
                        //Failure
                    }
                });
    }
}

manifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.geofencing">
    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/>
    <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">
         <service android:name=".GeofenceIntentService"/>
        <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>