Introduction to Groovy
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Introduction to Groovy, the next generation JVM programming language.
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Introduction to Groovy
- 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