Infinum android talks_10_getting groovy on android

Java on Android
• no Java 8 and lambda expressions
• writing a lot of boilerplate code

Groovy
• optionally typed
• dynamic language
• compiles into Java VM bytecode

Groovy
Thread thread = new Thread(new Runnable() { 
 
@Override 
void run() { 
//do stuff in background 
} 
});
• example (executing code in a new thread) on Java:

Groovy
• same thing in Groovy, using closures:
Thread.start { //do stuff in background }

Groovy
• more concise code
• more readable code
• still type safe
• still fast

Beneﬁts of Groovy
• semi colons are optional
• parentheses are optional
• dynamic typing
• return keyword is optional
• public keyword is optional
• all Java is valid Groovy

Default imports
• java.io.*
• java.lang.*
• java.math.BigDecimal
• java.math.BigInteger
• java.net.*
• java.util.*
• groovy.lang.*
• groovy.util.*

Special operators
• Elvis operator 
• ?. operator
def name = person.name ?: "unknown"
def name = person?.name

Initializers
• Java:
• Groovy:
int[] array = { 1, 2, 3}
int[] array = [1,2,3]
• { … } block reserved for closures

Initializers
def list = [1, 2, 3, 4 ,5] 
 
def map = [a: 1, b: 2, c:3] 
 
def regex = ~/.*foo.*/ 
 
def range = 128..255 
 
def closure = {a, b -> a + b}
• other available initializers:

== operator
• == in groovy translates to: 
a.compareTo(b) == 0 if they are Comparable 
a.equals(b) otherwise

Groovy truth
• in Java: 
• in Groovy: 
if(s)
if(s != null && s.length() > 0)

Package scope
• Java: package private ﬁeld
• Groovy: property
• package private ﬁeld in groovy:
class Person {
String name
}
class Person {
@PackageScope String name
}

Multi-methods
• java: result = 2 (method chosen at compile time)
• groovy: result = 1 (method chosen at run time)
int method(String arg) {
return 1;
}
int method(Object arg) {
return 2;
}
Object o = "Object";
int result = method(o);

Properties
public class Pokemon { 
 
private String name; 
 
public String getName() { 
return name; 
} 
 
public void setName(String name) { 
this.name = name; 
} 
}
Pokemon pokemon = new Pokemon(); 
pokemon.setName("Pikachu");
public class Pokemon { 
 
String name; 
}
Pokemon pokemon =
new Pokemon(name: "Pikachu") 
pokemon.setName("Raichu")

Annotation processing
• no annotation processing in Groovy
• AST transformations
• example: @Immutable - implements immutable “by
the book”

AST transformations example
public final class Person { 
 
private final String name; 
private final int age; 
 
public Person(String name, int age) { 
this.name = name; 
this.age = age; 
} 
 
public String getName() { 
return name; 
} 
 
public int getAge() { 
return age; 
} 
 
@Override 
public int hashCode() { 
return age + 31 * name.hashCode(); 
} 
 
@Override 
public boolean equals(Object other) { 
if(other == null) { 
return false; 
} 
 
if(this == other) { 
return true; 
} 
 
if(Person.class != other.getClass()) { 
return false; 
} 
 
Person otherPerson = (Person) other; 
if(!name.equals(otherPerson.name)) { 
return false; 
} 
 
if(age != otherPerson.age) { 
return false; 
} 
 
return true; 
} 
 
@Override 
public String toString() { 
return "Person(" + name + ", " + age + ")"; 
} 
}
import groovy.transform.Immutable 
 
@Immutable 
public class Person { 
String name; 
int age; 
}

with {} method
view = new TextView(context); 
view.setName(name); 
view.setTextSize(16f); 
view.setTextColor(Color.WHITE);
view = new TextView(context);
view.with { 
text = name 
textSize = 16f 
textColor = Color.WHITE 
}

Resource handling
File f = new File("/sdcard/dir/f.txt"); 
if(f.exists() && f.canRead()) { 
FileInputStream fis = null; 
try { 
fis = new FileInputStream(f); 
byte[] bytes = new byte[fis.available()]; 
while(fis.read(bytes) != -1) {}; 
textView.setText(new String(bytes)); 
} catch(IOException e) { 
//handle 
} finally { 
if(fis != null) { 
try { 
fis.close(); 
} catch(IOException e) { 
//ignore 
} 
} 
} 
} else { 
//handle 
}
def f = new File("/sdcard/dir/f.txt"); 
if(f.exists() && f.canRead()) { 
f.withInputStream { fis -> 
def bytes = new byte[fis.available()] 
while(fis.read(bytes) != -1) {} 
textView.setText(new String(bytes)) 
} 
}

HTTP GET example
def url = "https://api.github.com/repos" + 
"groovy/groovy-core/commits" 
def commits = new JsonSlurper().parseText(url.toURL().text) 
 
assert commits[0].commit.author.name == "Cedric Champeau"
• easy to parse JSON REST API:

But there is more
• all the differences are described: 
http://groovy-lang.org/differences.html

Modify build.gradle
buildscript { 
repositories { 
jcenter() 
} 
dependencies { 
classpath 'com.android.tools.build:gradle:1.0.1' 
classpath 'me.champeau.gradle:gradle-groovy-android-plugin:0.3.0' 
} 
} 
 
apply plugin: 'com.android.application' 
apply plugin: 'me.champeau.gradle.groovy-android' 
 
android { 
… 
} 
 
dependencies { 
compile fileTree(dir: 'libs', include: ['*.jar']) 
 
compile ‘org.codehaus.groovy:groovy-all:2.4.3' 
 
… 
}

Add groovy code
• rename class ﬁles from .java to .groovy
• Android Studio has autocomplete support!

Proguard
-dontobfuscate 
-keep class org.codehaus.groovy.reflection.** { *; } 
-keep class org.codehaus.groovy.vmplugin.** { *; } 
-keep class org.codehaus.groovy.runtime.dgm* { *; } 
-keepclassmembernames class org.codehaus.groovy.runtime.dgm* { 
*; 
} 
-keepclassmembernames class ** implements 
org.codehaus.groovy.runtime.GeneratedClosure { 
*; 
} 
-dontwarn org.codehaus.groovy.** 
-dontwarn groovy**

Groovy overhead
Java Groovy
Without
Proguard
947 kB 2.9 MB
With
Proguard
719 kB 1.6 MB

Libraries
• all Android libraries can be used with Groovy
• caveat: annotation processing won’t be run  
(except for .java ﬁles)

Swiss knife
• Butterknife for Groovy
• same annotations as Butterknife
• in onCreate() add:
SwissKnife.inject(this); 
SwissKnife.restoreState(this, savedInstanceState);
compile ‘com.arasthel:swissknife:1.2.3'
• in build.gradle add:

The good
• less boilerplate and more concise code
• closures
• neat Exception stacktraces for closures  
(vs Java 8 lambdas)

The bad
• a little bit slower than Java Android project
• larger .apk
• no annotation processing (APT)

Conclusion
• good for smaller projects
• faster to code
• lots of syntax sugar
• add some overhead to performance and .apk size

Resources
• Groovy presentation by Guillaume Laforge:  
https://speakerdeck.com/glaforge/groovy-on-
android-droidcon-paris-2014
• Groovy ofﬁcial site: 
http://groovy-lang.org/
• groovy project example: 
https://github.com/ikust/groovy-pokemons

Infinum android talks_10_getting groovy on android

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