Groovy Api Tutorial

You can define a variable without specifying TYPEdef user = new User()You can define function argumentswithout TYPEvoid testUser(user) { user.shout() }Types in Groovy1.1.getClass().name // java.math.BigDecimalMultimethordsExampleDynamic Type

import java.util.*;public class UsingCollection{public static void main(String[] args){ArrayList<String> lst = new ArrayList<String>();Collection<String> col = lst;lst.add("one" );lst.add("two" );lst.add("three" );lst.remove(0);col.remove(0);System.out.println("Added three items, remove two, so 1 item to remain." );System.out.println("Number of elements is: " + lst.size());System.out.println("Number of elements is: " + col.size());}}ExamplePlease Give Result running on Java & Groovy

One of The biggest contributions of GDK is extending the JDK with methods that take closures.Define a closuredef closure = { println “hello world”}ExampledefpickEven(n, block){for(inti = 2; i <= n; i += 2){ block(i)}}pickEvent(10, {println it})=== pickEvent(10) {println it} when closure is the last argumentdef Total = 0; pickEvent(10) {total += it}; println total Using Closures

When you curry( ) a closure, you’re asking the parameters to be prebound.ExampledeftellFortunes(closure){Date date = new Date("11/15/2007" )postFortune= closure.curry(date)postFortune "Your day is filled with ceremony"postFortune "They're features, not bugs"}tellFortunes() { date, fortune ->println"Fortune for ${date} is '${fortune}'"}Curried Closure

def examine(closure){println "$closure.maximumNumberOfParameters parameter(s) given:"for(aParameter in closure.parameterTypes) { println aParameter.name }}examine() { } // 1, Objectexamine() { it } // 1, Objectexamine() {-> } // 0examine() { val1 -> } // 1, Objectexamine() {Date val1 -> } // 1, Dateexamine() {Date val1, val2 -> } // 2, Date, Objectexamine() {Date val1, String val2 -> } // 2, Date, StringDynamic Closures

Three properties of a closure determine which object handles a method call from within a closure. These are this, owner, and delegate. Generally, the delegate is set to owner, but changing it allows you to exploit Groovy for some really good metaprogramming capabilities.Example ??? Closure Delegation

Creating String with ‘, “(GStringImpl), ‘’’(multiLine) getSubString using [] , “hello”[3], “hello”[1..3]As String in Java, String in Groovy is immutable.Working with String

Problemprice = 568.23company = 'Google'quote = "Today $company stock closed at $price"println quotestocks = [Apple : 130.01, Microsoft : 35.95]stocks.each { key, value ->company = keyprice = valueprintln quote}Why ? When you defined the GString—quote—you bound the variables company and price to a String holding the value Google and an Integer holding that obscene stock price, respectively. You can change the company and price references all you want (both of these are referring to immutable objects) to refer to other objects, but you’re not changing what the GString instance has been bound to.SolutionUsing closurequote = “Today ${->company} stock closed at ${->price}”GString Lazy Evaluation Problem

“hello world” -= “world” for(str in ‘abc’..’abz’){ print “${str} ”}Regular ExpressionsDefine pattern : def pattern = ~”[aAbB]”Matching=~ , ==~“Groovy is good” =~ /g|Groovy/ //match“Groovy is good” ==~ /g|Groovy/ //no match('Groovy is groovy, really groovy'=~ /groovy/).replaceAll(‘good' )String Convenience Methods

def a = [1,2,3,4,5,6,7] // ArrayListDef b = a[2..5] // b is an object of RandomAccessSubListUsing each for iterating over an lista.each { println it }Finder Methords: find & findAlla.find {it > 6} //7 return the first match resulta.findAll {it > 5} //[5,7] return a list include all matched membersConvenience Methodcollectinjectjoinflatten*List

def a = [s:1,d:2,f:3] //LinkedHashMapfetch value by Key: a.s, a[“s”]a.each {entry -> println “$entry.key : $entry.value” }a.each{key, value -> println“$key : $value” }MethodsCollect, find, findAllAny, everygroupByMap

The dump and inspect Methodsdump( ) lets you take a peek into an object.Println“hello”.dump()java.lang.String@5e918d2 value=[h, e, l, l, o] offset=0 count=5 hash=99162322Groovy also adds another method, inspect( ), to Object. This method is intended to tell you what input would be needed to create an object. If unimplemented on a class, it simply returns what toString( ) returns. If your object takes extensive input, this method will help users of your class figure out at runtime what input they should provide.Object Extensions

identity: The Context Methodlst = [1, 2]lst.identity {add(3)add(4)println size() //4println contains(2) // trueprintln "this is ${this}," //this is Identity@ce56f8,println "owner is ${owner}," //owner is Identity@ce56f8,println "delegate is ${delegate}." //delegate is [1, 2, 3, 4].}Object Extensions

Sleep: suppresses the Interrupted-Exception. If you do care to be interrupted, you don’t have to endure try-catch. Instead, in Groovy, you can use a variation of the previous sleep( ) method that accepts a closure to handle the interruption.new Object().sleep(2000) {println "Interrupted... " + itflag //if false, the thread will sleep 2 second as if there is no interruption}Object Extensions

class Car{int miles, fuelLevelvoid run(){println “boom …”}Void status(int a, String b) {println“$a --- $b”}}car = new Car(fuelLevel: 80, miles: 25)Indirect Property Accessprintln car[“miles”]Indirect Method Invokecar.invokeMethod(“status”, [1,”a”] as Object[])Object Extensions

Overloaded operators for Character, Integer, and so on. Such as plus( ) for operator +, next( ) for operator++, and so on.Number (which Integer and Double extend) has picked up the iterator methods upto( ) and downto( ). It also has the step( ) method.Thread.start{} & Thread.startDaemon()java.lang extensions

Read fileprintln new File('thoreau.txt' ).textnew File('thoreau.txt' ).eachLine { line ->println line}println new File('thoreau.txt' ).filterLine { it =~ /life/ }Write filenew File("output.txt" ).withWriter{ file -> file << "some data..."}java.io Extensions

Details about calling a methodGroovy Object

Use MetaClass to modify a class at runtimeDynamic Adding or modifying MethodA.metaclass.newMethod= { println “new method”}Dynamic Adding or modifying variableA.metaClass.newParam = 1After these, U cannew A().newMethod()println new A().newParamMetaClass

Implements GroovyInterceptable & define method invokeMethod(String name, args)Using MetaClassdefine a closure for metaclassCar.metaClass.invokeMethod = { String name, args->//…}Intercepting Methods

Groovy Api Tutorial

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