Realm Database version 3.0.0 example

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="np.gov.mof.budget">
  
    <!-- for internet -->
    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
  
    <!-- sd card read/write -->
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

    <!-- for alarm manager -->
    <uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED" />
    <uses-permission android:name="android.permission.VIBRATE" />
  
    <!-- android:name="AppController"  -->  <!-- This is added to initialize the realm database during app initialization. -->
    <application
        android:name="AppController"
        android:allowBackup="true"
        android:hardwareAccelerated="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme.NoActionBar">
        <activity
            android:name=".activity.SplashActivity"
            android:label="@string/app_name"
            android:theme="@style/AppTheme.Launch">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity
            android:name=".activity.MainActivity"
            android:label="@string/app_name"
            android:theme="@style/AppTheme.NoActionBar" />
      
      <!-- other activity in the app....  -->
 
    </application>

</manifest>

AppController.java

public class AppController extends Application{

    public static final String TAG = AppController.class.getSimpleName();

    private static AppController mInstance;

    @Override
    public void onCreate() {
        super.onCreate();

        // Initialize Realm
        Realm.init(this);

        //migration process here, since we donot worry about data loss database is destroyed if migration is needed.
        RealmConfiguration config = new RealmConfiguration.Builder()
                .deleteRealmIfMigrationNeeded()
                .build();
        Realm.setDefaultConfiguration(config);
    }
}

build.gradle (Module: app)

apply plugin: 'com.android.application'
apply plugin: 'realm-android'

android {
    compileSdkVersion 25
    buildToolsVersion "25.0.2"
    defaultConfig {
        applicationId "np.gov.mof.budget"
        minSdkVersion 16
        targetSdkVersion 25
        versionCode 1
        versionName "0.1"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {

    def SUPPORT = '25.1.1'
    compile project(':helperlib')
    //compile files('libs/YouTubeAndroidPlayerApi.jar')
    compile fileTree(dir: 'libs', include: ['*.jar'])
    androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
        exclude group: 'com.android.support', module: 'support-annotations'
    })
    testCompile 'junit:junit:4.12'

    //google
    compile "com.android.support:appcompat-v7:$SUPPORT"
    compile "com.android.support:design:$SUPPORT"
    compile "com.android.support:support-v4:$SUPPORT"
    compile "com.android.support:cardview-v7:$SUPPORT"
    compile "com.android.support:recyclerview-v7:$SUPPORT"

    compile 'com.google.code.gson:gson:2.6.2'

    //butternknife library
    compile 'com.jakewharton:butterknife:8.4.0'
    annotationProcessor 'com.jakewharton:butterknife-compiler:8.4.0'

    //expandable recyclerveiw
    compile 'com.bignerdranch.android:expandablerecyclerview:2.1.1'

    //square
    compile 'com.squareup.retrofit2:retrofit:2.1.0'
    compile 'com.squareup.retrofit2:converter-gson:2.1.0'

    //ion for network
    compile 'com.koushikdutta.ion:ion:2.1.9'

    //for charts
    compile 'com.github.PhilJay:MPAndroidChart:v3.0.1'
}

build.gradle (Project: YourProjectName)

// Top-level build file where you can add configuration options common to all sub-projects/modules.

buildscript {
    repositories {
        jcenter()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:2.3.0'

        //realm database
        classpath "io.realm:realm-gradle-plugin:3.0.0"

        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
    }
}

allprojects {
    repositories {
        jcenter()
        maven { url "https://jitpack.io" }
    }
}

task clean(type: Delete) {
    delete rootProject.buildDir
}

MainActivity.java

public class MainActivity extends AppCompatActivity {
  
  @Override
    protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
      Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
      setSupportActionBar(toolbar);
     
      Realm realm = Realm.getDefaultInstance();
      
      List<User> userArrayList = new ArrayList<>();
      
      //creating object which is not managed by realm
      User user = new User();
      user.setName("Kishor");
      user.setAddress("Sanepa");
      
      User anotherUser = new User();
      anotherUser.setName("Sagar");
      anotherUser.setAddress("Satdobato");
      
      userArrayList.add(user);
      userArrayList.add(anotherUser)
      
      //inserting the object to realm database
      realm.beginTransaction;
      user = realm.copyToRealm(user); //user is now managed object which can only be updated inside transaction only
      user.setAddress("Lalitpur");
      realm.commitTransaction;
      
      
      realm.beginTransaction;
      realm.copyToRealm(anotherUser);  //anotherUser is inserted 
      realm.copyToRealm(userArrayList);//list is inserted to database
      realm.commitTransaction;
      
      //reading objects from realm, no need of beginTransaction while reading from realm
      RealmResults<User> userList = realm.where(User.class).findAll;
      RealmResults<User> usersAtLalipur = realm.where(User.class).equalTo("address","Lalitpur").findAll;
      User sagar = realm.where(User.class).equalTo("name","Sagar").findFirst();
      
    }
  
}

User.java

public class User extends RealmObject{
    private String name;
    private String address;
    
    //getter and setter or constructor or custom methods
    
}