feat: multicast playground

README.md

@@ -26,6 +26,8 @@ I've also been giving talks about Learning Rx using many of the examples listed
 14. [Pagination with Rx (using Subjects)](#14-pagination-with-rx-using-subjects)
 15. [Orchestrating Observable: make parallel network calls, then combine the result into a single data point (using flatmap & zip)](#15-orchestrating-observable-make-parallel-network-calls-then-combine-the-result-into-a-single-data-point-using-flatmap--zip)
 16. [Simple Timeout example (using timeout)](#16-simple-timeout-example-using-timeout)
+17. [Setup and teardown resources (using `using`)](#17-setup-and-teardown-resources-using-using)
+18. [Multicast playground](#18-multicast-playground)
 
 ## Description
 
@@ -161,7 +163,7 @@ Cases demonstrated here:
 4. run a task constantly every 3s, but after running it 5 times, terminate automatically
 5. run a task A, pause for sometime, then execute Task B, then terminate
 
-### 11. RxBus : event bus using RxJava (using RxRelay (never terminating Subjects) and debouncedBuffer)  
+### 11. RxBus : event bus using RxJava (using RxRelay (never terminating Subjects) and debouncedBuffer)
 
 There are accompanying blog posts that do a much better job of explaining the details on this demo:
 
@@ -222,6 +224,20 @@ This is a simple example demonstrating the use of the `.timeout` operator. Butto
 
 Notice how we can provide a custom Observable that indicates how to react under a timeout Exception.
 
+### 17. Setup and teardown resources (using `using`)
+
+The [operator `using`](http://reactivex.io/documentation/operators/using.html) is relatively less known and notoriously hard to Google. It's a beautiful API that helps to setup a (costly) resource, use it and then dispose off in a clean way.
+
+The nice thing about this operator is that it provides a mechansim to use potentially costly resources in a tightly scoped manner. using -> setup, use and dispose. Think DB connections (like Realm instances), socket connections, thread locks etc.
+
+### 18. Multicast Playground
+
+Multicasting in Rx is like a dark art. Not too many folks know how to pull it off without concern. This example condiers two subscribers (in the forms of buttons) and allows you to add/remove subscribers at different points of time and see how the different operators behave under those circumstances.
+
+The source observale is a timer (`interval`) observable and the reason this was chosen was to intentionally pick a non-terminating observable, so you can test/confirm if your multicast experiment will leak.
+
+_I also gave a talk about [Multicasting in detail at 360|Andev](https://speakerdeck.com/kaushikgopal/rx-by-example-volume-3-the-multicast-edition). If you have the inclination and time, I highly suggest watching that talk first (specifically the Multicast operator permutation segment) and then messing around with the example here._
+
 ## Rx 2.x
 
 All the examples here have been migrated to use RxJava 2.X.

app/build.gradle

@@ -18,13 +18,14 @@ apply plugin: 'com.f2prateek.javafmt'
 apply plugin: 'kotlin-android'
 
 dependencies {
+    compile 'com.android.support:multidex:1.0.1'
     compile "com.android.support:support-v13:${supportLibVersion}"
     compile "com.android.support:appcompat-v7:${supportLibVersion}"
     compile "com.android.support:recyclerview-v7:${supportLibVersion}"
 
     compile 'com.github.kaushikgopal:CoreTextUtils:c703fa12b6'
     compile "com.jakewharton:butterknife:${butterKnifeVersion}"
-    annotationProcessor "com.jakewharton:butterknife-compiler:${butterKnifeVersion}"
+    kapt "com.jakewharton:butterknife-compiler:${butterKnifeVersion}"
     compile 'com.jakewharton.timber:timber:4.5.1'
     compile "com.squareup.retrofit2:retrofit:${retrofitVersion}"
     compile "com.squareup.retrofit2:converter-gson:${retrofitVersion}"
@@ -44,8 +45,10 @@ dependencies {
     // explicitly depend on RxJava's latest version for bug fixes and new features.
     compile 'io.reactivex.rxjava2:rxandroid:2.0.1'
 
+    compile 'com.jakewharton.rx:replaying-share-kotlin:2.0.0'
     compile "com.github.akarnokd:rxjava2-extensions:0.16.0"
     compile 'com.jakewharton.rxrelay2:rxrelay:2.0.0'
+
     compile 'com.jakewharton.rxbinding2:rxbinding:2.0.0'
     compile 'com.jakewharton.retrofit:retrofit2-rxjava2-adapter:1.0.0'
 
@@ -65,6 +68,7 @@ android {
         targetSdkVersion sdkVersion
         versionCode 2
         versionName "1.2"
+        multiDexEnabled true
     }
     buildTypes {
         release {

app/src/main/java/com/morihacky/android/rxjava/MyApp.java

@@ -1,12 +1,12 @@
 package com.morihacky.android.rxjava;
 
-import android.app.Application;
+import android.support.multidex.MultiDexApplication;
 import com.morihacky.android.rxjava.volley.MyVolley;
 import com.squareup.leakcanary.LeakCanary;
 import com.squareup.leakcanary.RefWatcher;
 import timber.log.Timber;
 
-public class MyApp extends Application {
+public class MyApp extends MultiDexApplication {
 
   private static MyApp _instance;
   private RefWatcher _refWatcher;

app/src/main/java/com/morihacky/android/rxjava/fragments/MainFragment.java

@@ -116,6 +116,16 @@ void demoNetworkDetector() {
     clickedOn(new NetworkDetectorFragment());
   }
 
+  @OnClick(R.id.btn_demo_using)
+  void demoUsing() {
+    clickedOn(new UsingFragment());
+  }
+
+  @OnClick(R.id.btn_demo_multicastPlayground)
+  void demoMulticastPlayground() {
+    clickedOn(new MulticastPlaygroundFragment());
+  }
+
   private void clickedOn(@NonNull Fragment fragment) {
     final String tag = fragment.getClass().toString();
     getActivity()

app/src/main/kotlin/com/morihacky/android/rxjava/ext/RxExt.kt

@@ -0,0 +1,11 @@
+package com.morihacky.android.rxjava.ext
+
+import io.reactivex.disposables.CompositeDisposable
+import io.reactivex.disposables.Disposable
+
+operator fun CompositeDisposable.plus(disposable: Disposable): CompositeDisposable {
+    add(disposable)
+    return this
+}
+
+

app/src/main/kotlin/com/morihacky/android/rxjava/fragments/MulticastPlaygroundFragment.kt

@@ -0,0 +1,166 @@
+package com.morihacky.android.rxjava.fragments
+
+import android.content.Context
+import android.os.Bundle
+import android.os.Handler
+import android.os.Looper
+import android.view.LayoutInflater
+import android.view.View
+import android.view.ViewGroup
+import android.widget.*
+import butterknife.BindView
+import butterknife.ButterKnife
+import butterknife.OnClick
+import com.jakewharton.rx.replayingShare
+import com.morihacky.android.rxjava.R
+import io.reactivex.Observable
+import io.reactivex.disposables.Disposable
+import java.util.concurrent.TimeUnit
+
+class MulticastPlaygroundFragment : BaseFragment() {
+
+    @BindView(R.id.list_threading_log) lateinit var logList: ListView
+    @BindView(R.id.dropdown) lateinit var pickOperatorDD: Spinner
+    @BindView(R.id.msg_text) lateinit var messageText: TextView
+
+    private lateinit var sharedObservable: Observable<Long>
+    private lateinit var adapter: LogAdapter
+
+    private var logs: MutableList<String> = ArrayList()
+    private var disposable1: Disposable? = null
+    private var disposable2: Disposable? = null
+
+    override fun onCreateView(inflater: LayoutInflater?,
+                              container: ViewGroup?,
+                              savedInstanceState: Bundle?): View? {
+        val layout = inflater!!.inflate(R.layout.fragment_multicast_playground, container, false)
+        ButterKnife.bind(this, layout)
+
+        _setupLogger()
+        _setupDropdown()
+
+        return layout
+    }
+
+    @OnClick(R.id.btn_1)
+    fun onBtn1Click() {
+
+        disposable1?.let {
+            it.dispose()
+            _log("subscriber 1 disposed")
+            disposable1 = null
+            return
+        }
+
+        disposable1 =
+                sharedObservable
+                        .doOnSubscribe { _log("subscriber 1 (subscribed)") }
+                        .subscribe({ long -> _log("subscriber 1: onNext $long") })
+
+    }
+
+    @OnClick(R.id.btn_2)
+    fun onBtn2Click() {
+        disposable2?.let {
+            it.dispose()
+            _log("subscriber 2 disposed")
+            disposable2 = null
+            return
+        }
+
+        disposable2 =
+                sharedObservable
+                        .doOnSubscribe { _log("subscriber 2 (subscribed)") }
+                        .subscribe({ long -> _log("subscriber 2: onNext $long") })
+    }
+
+    @OnClick(R.id.btn_3)
+    fun onBtn3Click() {
+        logs = ArrayList<String>()
+        adapter.clear()
+    }
+
+    // -----------------------------------------------------------------------------------
+    // Method that help wiring up the example (irrelevant to RxJava)
+
+    private fun _log(logMsg: String) {
+
+        if (_isCurrentlyOnMainThread()) {
+            logs.add(0, logMsg + " (main thread) ")
+            adapter.clear()
+            adapter.addAll(logs)
+        } else {
+            logs.add(0, logMsg + " (NOT main thread) ")
+
+            // You can only do below stuff on main thread.
+            Handler(Looper.getMainLooper()).post {
+                adapter.clear()
+                adapter.addAll(logs)
+            }
+        }
+    }
+
+    private fun _setupLogger() {
+        logs = ArrayList<String>()
+        adapter = LogAdapter(activity, ArrayList<String>())
+        logList.adapter = adapter
+    }
+
+    private fun _setupDropdown() {
+        pickOperatorDD.adapter = ArrayAdapter<String>(context,
+                android.R.layout.simple_spinner_dropdown_item,
+                arrayOf(".publish().refCount()",
+                        ".publish().autoConnect(2)",
+                        ".replay(1).autoConnect(2)",
+                        ".replay(1).refCount()",
+                        ".replayingShare()"))
+
+
+        pickOperatorDD.onItemSelectedListener = object : AdapterView.OnItemSelectedListener {
+
+            override fun onItemSelected(p0: AdapterView<*>?, p1: View?, index: Int, p3: Long) {
+
+                val sourceObservable = Observable.interval(0L, 3, TimeUnit.SECONDS)
+                        .doOnSubscribe { _log("observer (subscribed)") }
+                        .doOnDispose { _log("observer (disposed)") }
+                        .doOnTerminate { _log("observer (terminated)") }
+
+                sharedObservable =
+                        when (index) {
+                            0 -> {
+                                messageText.setText(R.string.msg_demo_multicast_publishRefCount)
+                                sourceObservable.publish().refCount()
+                            }
+                            1 -> {
+                                messageText.setText(R.string.msg_demo_multicast_publishAutoConnect)
+                                sourceObservable.publish().autoConnect(2)
+                            }
+                            2 -> {
+                                messageText.setText(R.string.msg_demo_multicast_replayAutoConnect)
+                                sourceObservable.replay(1).autoConnect(2)
+                            }
+                            3 -> {
+                                messageText.setText(R.string.msg_demo_multicast_replayRefCount)
+                                sourceObservable.replay(1).refCount()
+                            }
+                            4 -> {
+                                messageText.setText(R.string.msg_demo_multicast_replayingShare)
+                                sourceObservable.replayingShare()
+                            }
+                            else -> throw RuntimeException("got to pick an op yo!")
+                        }
+            }
+
+            override fun onNothingSelected(p0: AdapterView<*>?) {}
+        }
+    }
+
+    private fun _isCurrentlyOnMainThread(): Boolean {
+        return Looper.myLooper() == Looper.getMainLooper()
+    }
+
+    private inner class LogAdapter(context: Context, logs: List<String>) :
+            ArrayAdapter<String>(context, R.layout.item_log, R.id.item_log, logs)
+
+}
+

app/src/main/java/com/morihacky/android/rxjava/fragments/PlaygroundFragment.kt → app/src/main/kotlin/com/morihacky/android/rxjava/fragments/PlaygroundFragment.kt

@@ -16,25 +16,21 @@ class PlaygroundFragment : BaseFragment() {
     private var _logsList: ListView? = null
     private var _adapter: LogAdapter? = null
 
-    private var _attempt = 0
     private var _logs: MutableList<String> = ArrayList()
 
     override fun onCreateView(inflater: LayoutInflater?,
                               container: ViewGroup?,
                               savedInstanceState: Bundle?): View? {
-        return inflater!!.inflate(R.layout.fragment_concurrency_schedulers, container, false)
-    }
-
-    override fun onActivityCreated(savedInstanceState: Bundle?) {
-        super.onActivityCreated(savedInstanceState)
+        val view = inflater?.inflate(R.layout.fragment_concurrency_schedulers, container, false)
 
-        _logsList = activity.findViewById(R.id.list_threading_log) as ListView
+        _logsList = view?.findViewById(R.id.list_threading_log) as ListView
+        _setupLogger()
 
-        activity.findViewById(R.id.btn_start_operation).setOnClickListener { _ ->
+        view.findViewById(R.id.btn_start_operation).setOnClickListener { _ ->
             _log("Button clicked")
         }
 
-        _setupLogger()
+        return view
     }
 
     // -----------------------------------------------------------------------------------
@@ -44,23 +40,23 @@ class PlaygroundFragment : BaseFragment() {
 
         if (_isCurrentlyOnMainThread()) {
             _logs.add(0, logMsg + " (main thread) ")
-            _adapter!!.clear()
-            _adapter!!.addAll(_logs)
+            _adapter?.clear()
+            _adapter?.addAll(_logs)
         } else {
             _logs.add(0, logMsg + " (NOT main thread) ")
 
             // You can only do below stuff on main thread.
             Handler(Looper.getMainLooper()).post {
-                _adapter!!.clear()
-                _adapter!!.addAll(_logs)
+                _adapter?.clear()
+                _adapter?.addAll(_logs)
             }
         }
     }
 
     private fun _setupLogger() {
         _logs = ArrayList<String>()
         _adapter = LogAdapter(activity, ArrayList<String>())
-        _logsList!!.adapter = _adapter
+        _logsList?.adapter = _adapter
     }
 
     private fun _isCurrentlyOnMainThread(): Boolean {

app/src/main/kotlin/com/morihacky/android/rxjava/fragments/UsingFragment.kt

@@ -0,0 +1,94 @@
+package com.morihacky.android.rxjava.fragments
+
+import android.content.Context
+import android.os.Bundle
+import android.os.Handler
+import android.os.Looper
+import android.view.LayoutInflater
+import android.view.View
+import android.view.ViewGroup
+import android.widget.ArrayAdapter
+import android.widget.ListView
+import android.widget.TextView
+import com.morihacky.android.rxjava.R
+import io.reactivex.Flowable
+import io.reactivex.functions.Consumer
+import io.reactivex.functions.Function
+import org.reactivestreams.Publisher
+import timber.log.Timber
+import java.util.*
+import java.util.concurrent.Callable
+
+class UsingFragment : BaseFragment() {
+
+    private lateinit var _logs: MutableList<String>
+    private lateinit var _logsList: ListView
+    private lateinit var _adapter: UsingFragment.LogAdapter
+
+    override fun onCreateView(inflater: LayoutInflater?, container: ViewGroup?, savedInstanceState: Bundle?): View? {
+        val view = inflater?.inflate(R.layout.fragment_buffer, container, false)
+        _logsList = view?.findViewById(R.id.list_threading_log) as ListView
+
+        (view.findViewById(R.id.text_description) as TextView).setText(R.string.msg_demo_using)
+
+        _setupLogger()
+        view.findViewById(R.id.btn_start_operation).setOnClickListener { executeUsingOperation() }
+        return view
+    }
+
+    private fun executeUsingOperation() {
+        val resourceSupplier = Callable<Realm> { Realm() }
+        val sourceSupplier = Function<Realm, Publisher<Int>> { realm ->
+            Flowable.just(true)
+                    .map {
+                        realm.doSomething()
+                        // i would use the copyFromRealm and change it to a POJO
+                        Random().nextInt(50)
+                    }
+        }
+        val disposer = Consumer<Realm> { realm ->
+            realm.clear()
+        }
+
+        Flowable.using(resourceSupplier, sourceSupplier, disposer)
+                .subscribe({ i ->
+                    _log("got a value $i - (look at the logs)")
+                })
+    }
+
+    inner class Realm {
+        init {
+            Timber.d("--- initializing Realm instance")
+        }
+
+        fun doSomething() {
+            Timber.d("--- do something with Realm instance")
+        }
+
+        fun clear() {
+            // notice how this is called even before you manually "dispose"
+            Timber.d("--- cleaning up the resources (happens before a manual 'dispose'")
+        }
+    }
+
+    // -----------------------------------------------------------------------------------
+    // Method that help wiring up the example (irrelevant to RxJava)
+
+    private fun _log(logMsg: String) {
+        _logs.add(0, logMsg)
+
+        // You can only do below stuff on main thread.
+        Handler(Looper.getMainLooper()).post {
+            _adapter.clear()
+            _adapter.addAll(_logs)
+        }
+    }
+
+    private fun _setupLogger() {
+        _logs = ArrayList<String>()
+        _adapter = LogAdapter(activity, ArrayList<String>())
+        _logsList.adapter = _adapter
+    }
+
+    private class LogAdapter(context: Context, logs: List<String>) : ArrayAdapter<String>(context, R.layout.item_log, R.id.item_log, logs)
+}

app/src/main/res/layout/fragment_buffer.xml

@@ -7,7 +7,8 @@
     >
 
     <TextView
-        android:layout_height="wrap_content"
+      android:id="@+id/text_description"
+      android:layout_height="wrap_content"
         android:layout_width="match_parent"
         android:padding="10dp"
         android:gravity="center"

app/src/main/res/layout/fragment_main.xml

@@ -127,5 +127,19 @@
             android:layout_width="match_parent"
             android:text="@string/btn_demo_networkDetector"
             />
+
+        <Button
+            android:id="@+id/btn_demo_using"
+            android:layout_height="wrap_content"
+            android:layout_width="match_parent"
+            android:text="@string/btn_demo_using"
+            />
+
+        <Button
+            android:id="@+id/btn_demo_multicastPlayground"
+            android:layout_height="wrap_content"
+            android:layout_width="match_parent"
+            android:text="@string/btn_demo_multicastPlayground"
+            />
     </LinearLayout>
 </ScrollView>

app/src/main/res/layout/fragment_multicast_playground.xml

@@ -0,0 +1,72 @@
+<?xml version="1.0" encoding="utf-8"?>
+<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
+  android:layout_width="match_parent"
+  android:layout_height="match_parent"
+  android:orientation="vertical">
+
+
+  <TableLayout
+    android:layout_width="match_parent"
+    android:layout_height="wrap_content">
+
+    <TableRow
+      android:layout_width="match_parent"
+      android:layout_height="wrap_content"
+      android:gravity="center">
+
+      <Spinner
+        android:id="@+id/dropdown"
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:layout_span="3"/>
+
+    </TableRow>
+
+    <TableRow
+      android:layout_width="match_parent"
+      android:layout_height="wrap_content">
+
+      <TextView
+        android:id="@+id/msg_text"
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:layout_weight="1"
+        android:layout_span="3"
+        android:padding="@dimen/text_micro"
+        android:text="@string/msg_demo_multicast_publishRefCount"/>
+    </TableRow>
+
+    <TableRow
+      android:layout_width="match_parent"
+      android:layout_height="wrap_content">
+
+      <Button
+        android:id="@+id/btn_1"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_weight="1"
+        android:text="Subscribe 1"/>
+
+      <Button
+        android:id="@+id/btn_2"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_weight="1"
+        android:text="Subscribe 2"/>
+
+      <Button
+        android:id="@+id/btn_3"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_weight="1"
+        android:text="Clear log"/>
+    </TableRow>
+
+  </TableLayout>
+
+
+  <ListView
+    android:id="@+id/list_threading_log"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent"/>
+</LinearLayout>

app/src/main/res/values/strings.xml

@@ -23,6 +23,8 @@
     <string name="btn_demo_pagination">Paging example</string>
     <string name="btn_demo_pagination_more">MOAR</string>
     <string name="btn_demo_networkDetector">Network Detector (Subject)</string>
+    <string name="btn_demo_using">Setup &amp; teardown resources (using)</string>
+    <string name="btn_demo_multicastPlayground">MultiConnect operator playground</string>
 
     <string name="msg_demo_pagination">This is a demo of how you can do a list pagination with Rx. We page 10 items at a time and there are 55 items altogether</string>
     <string name="msg_demo_volley">This is a Volley request demo</string>
@@ -40,6 +42,12 @@
     <string name="msg_demo_timing">BTN 1: run single task once (after 2s complete)\nBTN 2: run task every 1s (start delay of 1s) toggle \nBTN 3: run task every 1s (start immediately) toggle \nBTN 4: run task 5 times every 3s (then complete) \nBTN 5: run task A, pause for sometime, then proceed with Task B</string>
     <string name="msg_demo_rotation_persist">This is an example of starting an Observable and using the result across rotations. There are many ways to do this, we use a retained fragment in this example</string>
     <string name="msg_demo_network_detector">This is a demo of how to use Subjects to detect Network connectivity\nToggle your Wifi/Network on or off and notice the logs</string>
+    <string name="msg_demo_using">This is a demo of the somewhat unknown operator "using".\n\nmsg_demo_usingYou typically use it for managing setup/teardown of resources. Classic cases are DB connections (like Realm), sockets, locks etc.\n\nTap the button and look at the logcat. Particularly notice how the Realm instance is self-contained. That is, it is auto-disposed right after use.</string>
+    <string name="msg_demo_multicast_publishRefCount">RefCount starts the upstream right away and gets disposed off, when all subscribers stop. Hit S1, Hit S2, Hit S1, Hit S2. Hit S1/S2 now and notice the stream starts all over.</string>
+    <string name="msg_demo_multicast_publishAutoConnect">AutoConnect(2) waits for a min. subscriber count, before starting the upstream. Hit S1 (notice events don\'t start), Hit S2 (notice events now start), Hit S1 (notice that unsubscribing doesn\'t affect upstream), Hit S2, wait for sometime and hit S1 again (notice source stream doesn\'t restart)</string>
+    <string name="msg_demo_multicast_replayAutoConnect">Replay caches the last item. Hit S1, Hit S2, event starts, Hit S2, wait a bit, Hit S2 again (notice it starts with the last item that S1 saw - courtesy Replay). Hit S2, Hit S1, wait a bit. Hit S1 again (notice event upstream continues and doesn\'t restart)</string>
+    <string name="msg_demo_multicast_replayRefCount">Replay caches the last item. Hit S1, wait a bit, then hit S2 (notice S2 starts immediately with last item that S1 saw), Hit S2, Hit S1. Hit S1/S2 again (notice the stream restarts all over. Interestingly cached last item also removed when both subscribers released)</string>
+    <string name="msg_demo_multicast_replayingShare">Courtesy: new #AndroidDev on the block - JakeWharton. exactly like replay(1).refCount(), but caches the last item even when upstream has been disposed off/released. Hit S1, Hit S2, Hit S1, Hit S2 (notice observable is disposed). Hit S1/S2 again (notice we start with last item emitted)</string>
 
     <string name="msg_pseudoCache_demoInfo_concat">Concat merges the results sequentially. But notice that the latter subscription starts only AFTER the first one completes. Some unnecessary waiting there.</string>
     <string name="msg_pseudoCache_demoInfo_concatEager">Concat eager is cooler. Both subscriptions start at the same time (parallely) but the order of emission is respected.</string>

build.gradle

@@ -6,7 +6,7 @@ buildscript {
         mavenCentral()
     }
     dependencies {
-        classpath 'com.android.tools.build:gradle:2.3.2'
+        classpath 'com.android.tools.build:gradle:2.3.3'
         classpath 'com.f2prateek.javafmt:javafmt:0.1.2'
 
         // NOTE: Do not place your application dependencies here; they belong
@@ -26,7 +26,7 @@ allprojects {
         sdkVersion = 24
         buildToolsVrs = "25.0.0"
 
-        kotlinVersion = "1.1.2-4"
+        kotlinVersion = "1.1.3-2"
 
         butterKnifeVersion = '8.5.1'
         mockitoKotlinVersion = "1.4.0"

gradle/wrapper/gradle-wrapper.properties

@@ -3,4 +3,4 @@ distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-3.5-all.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-4.0-all.zip