Introduction to Groovy, the next generation JVM programming language.

1. Introduction to Groovy
The next generation JVM programming language

2. What is Groovy?
• Scripting language
• Programming Language
• runs on JVM
• dynamic
• derived from Java
• JSR-241
• started from 2003

3. Problem with Java
• Primitive data types, defies the nature of OO
programming

4. Why Groovy
• Easier than Java syntax
• Fully compatible with Java
• Easy to find workarounds since Java code can be
compiled
• Principle of least surprises

5. Use Cases
• Scripting instead of Sh, Perl, Python, Ruby, etc
• Simpler ways of writing unit tests, stub and mocks
• Configuration/Dependency Management in Gradle
!
• Full blown applications via Grails and Griffon

6. Groovy Features
Everything is an object, including numbers
Example:
5.times{
println “ho”
}
(NOTE: Curly braces is a Closure)

7. Groovy Features
• Dynamic data type / Explicit typing
def b = 2
def is a reference, asks the compiler to figure out for
itself.

8. Groovy Features
• Objects
new User(name: ‘Kevin’, email:’kevin@kevin.com’)

9. Groovy Features
• Collections
New collection type - Range
Eg.
1..5 (inclusive, range from 1 to 5) or
1..<5 (exclusive, range from 1 to 4)

10. Groovy Features
• Collections
Iterator, eg.
r.each { n->
println n
}
or
r.each { println it }
(where ‘it’ is a reserved word)

11. Groovy Features
• Syntactic sugar for List
def countries = [“Malaysia”, “Thailand”]

12. Groovy Features
• Adding or removing values
list += “Singapore” becomes [“Malaysia”, “Thailand”,
“Singapore”]
!
list = list - [“Singapore”] becomes [“Malaysia”,
“Thailand”]

13. Groovy Features
Map
def person = [name:”Kevin”, age:”27”]!
println person.name <- how you access the value

14. Groovy Features
• New for loop syntax
for(i in 1..5){!
println i!
}!
but Java loop syntax is supported anyways.

15. Groovy Features
Operator overloading
a + b (Java) becomes a.plus(b) (Groovy)
a++ or ++a (Java) becomes a.next() (Groovy)
switch(a) { case b: } becomes b.isCase(a)
More info: http://groovy.codehaus.org/Operator+Overloading

16. Groovy Features
• Switch statement is more general than Java, eg:
switch (val) {
case it > 3:
break
case 5..9:
break
case Number:
break
}

17. Groovy Features
• Groovy Truth
standard conditional operators on boolean
expressions
&
boolean expressions for collections (empty
collections = false)

18. Groovy Features
• Groovy Truth
Applies for Maps, iterations and enums, objects,
numbers
!
http://groovy.codehaus.org/Groovy+Truth

19. Groovy Features
• Closures : High Order Functions
Idea : Methods are like objects, anonymous class in steroids
Treated as a “code block” to be executed later, eg.
def testClosure = {
println “test closure”
}

20. Groovy Features
• Closures : High Order Functions
with parameters eg.
def methodName = { n, r ->
… do something
}
To call the method,
method(n, r)

21. Groovy Features
• File I/O
def count=0, MAXSIZE=100
new File("foo.txt").withReader { reader ->
while (reader.readLine() != null) {
if (++count > MAXSIZE) throw new RuntimeException('File too
large!')
}
}

22. Groovy Features
• File I/O
def fields = ["a":"1", "b":"2", "c":"3"]
new File("foo.ini").withWriter { out ->
fields.each() { key, value ->
out.writeLine("${key}=${value}")
}
}

23. More References
• Groovy http://groovy.codehaus.org
• Grails (www.grails.org) for Web development
• Griffon (www.griffon.org) for desktop app
development

24. Contacts
• http://gplus.to/kevintanhongann