1. init project

2. create product flavor 'dev', 'prod' and 'mock'
3. create FlavorObject class and print method

.gitignore

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+*.iml
+.gradle
+/local.properties
+/.idea/workspace.xml
+/.idea/libraries
+.DS_Store
+/build
+/captures
+.externalNativeBuild

app/.gitignore

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+/build

app/build.gradle

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+apply plugin: 'com.android.application'
+
+android {
+    compileSdkVersion 25
+    buildToolsVersion "25.0.2"
+    defaultConfig {
+        applicationId "tw.andyang.multipleflavor"
+        minSdkVersion 21
+        targetSdkVersion 25
+        versionCode 1
+        versionName "1.0"
+        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
+    }
+    buildTypes {
+        release {
+            minifyEnabled false
+            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
+        }
+    }
+    productFlavors {
+        prod {
+
+        }
+        dev {
+
+        }
+        mock {
+
+        }
+    }
+}
+
+dependencies {
+    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'
+    })
+    compile 'com.android.support:appcompat-v7:25.2.0'
+    compile 'com.android.support.constraint:constraint-layout:1.0.0-alpha8'
+    testCompile 'junit:junit:4.12'
+}

app/proguard-rules.pro

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+# Add project specific ProGuard rules here.
+# By default, the flags in this file are appended to flags specified
+# in /Users/andy/Library/Android/sdk/tools/proguard/proguard-android.txt
+# You can edit the include path and order by changing the proguardFiles
+# directive in build.gradle.
+#
+# For more details, see
+#   http://developer.android.com/guide/developing/tools/proguard.html
+
+# Add any project specific keep options here:
+
+# If your project uses WebView with JS, uncomment the following
+# and specify the fully qualified class name to the JavaScript interface
+# class:
+#-keepclassmembers class fqcn.of.javascript.interface.for.webview {
+#   public *;
+#}
+
+# Uncomment this to preserve the line number information for
+# debugging stack traces.
+#-keepattributes SourceFile,LineNumberTable
+
+# If you keep the line number information, uncomment this to
+# hide the original source file name.
+#-renamesourcefileattribute SourceFile

app/src/androidTest/java/tw/andyang/multipleflavor/ExampleInstrumentedTest.java

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+package tw.andyang.multipleflavor;
+
+import android.content.Context;
+import android.support.test.InstrumentationRegistry;
+import android.support.test.runner.AndroidJUnit4;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import static org.junit.Assert.*;
+
+/**
+ * Instrumentation test, which will execute on an Android device.
+ *
+ * @see <a href="http://d.android.com/tools/testing">Testing documentation</a>
+ */
+@RunWith(AndroidJUnit4.class)
+public class ExampleInstrumentedTest {
+    @Test
+    public void useAppContext() throws Exception {
+        // Context of the app under test.
+        Context appContext = InstrumentationRegistry.getTargetContext();
+
+        assertEquals("tw.andyang.multipleflavor", appContext.getPackageName());
+    }
+}

app/src/dev/java/tw/andyang/multipleflavor/FlavorObject.java

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+package tw.andyang.multipleflavor;
+
+import android.util.Log;
+
+class FlavorObject {
+
+    private static final String TAG = "FlavorObject";
+
+    void print(){
+        Log.d(TAG, "dev FlavorObject");
+    }
+}

app/src/main/AndroidManifest.xml

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+<?xml version="1.0" encoding="utf-8"?>
+<manifest xmlns:android="http://schemas.android.com/apk/res/android"
+    package="tw.andyang.multipleflavor">
+
+    <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>