Tested and working on android 4.2+.

app/build.gradle

@@ -41,9 +41,15 @@ android {
         abortOnError false
     }
 
+    compileOptions {
+        sourceCompatibility JavaVersion.VERSION_1_7
+        targetCompatibility JavaVersion.VERSION_1_7
+    }
+
 }
 
 dependencies {
+    compile 'com.android.support:multidex:1.0.0'
     compile project(':ethereumj-core')
     compile fileTree(include: ['*.jar'], dir: '../libraries')
     //compile 'com.android.support:appcompat-v7:21.0.3'
@@ -52,4 +58,4 @@ dependencies {
     //compile "org.slf4j:slf4j-android:1.6.1-RC1"
     compile 'com.android.support:support-v4:22.1.1'
     compile 'com.android.support:appcompat-v7:22.1.1'
-}
+}

app/src/main/AndroidManifest.xml

@@ -9,6 +9,7 @@
         android:icon="@mipmap/ic_launcher"
         android:label="@string/app_name"
         android:theme="@style/AppTheme"
+        android:name="android.support.multidex.MultiDexApplication"
         android:largeHeap="true">
         <activity
             android:name=".MainActivity"
@@ -27,4 +28,4 @@
         </service>
     </application>
 
-</manifest>
+</manifest>