Groovy 中的设计模式

class TwoupMessages {
    def welcome = 'Welcome to the twoup game, you start with $1000'
    def done = 'Sorry, you have no money left, goodbye'
}

class TwoupInputConverter {
    def convert(input) { input.toInteger() }
}

class TwoupControl {
    private money = 1000
    private random = new Random()
    private tossWasHead() {
        def next = random.nextInt()
        return next % 2 == 0
    }
    def moreTurns() {
        if (money > 0) {
            println "You have $money, how much would you like to bet?"
            return true
        }

        false
    }
    def play(amount) {
        def coin1 = tossWasHead()
        def coin2 = tossWasHead()
        if (coin1 && coin2) {
            money += amount
            println 'You win'
        } else if (!coin1 && !coin2) {
            money -= amount
            println 'You lose'
        } else {
            println 'Draw'
        }
    }
}

class GuessGameMessages {
    def welcome = 'Welcome to the guessing game, my secret number is between 1 and 100'
    def done = 'Correct'
}

class GuessGameInputConverter {
    def convert(input) { input.toInteger() }
}

class GuessGameControl {
    private lower = 1
    private upper = 100
    private guess = new Random().nextInt(upper - lower) + lower
    def moreTurns() {
        def done = (lower == guess || upper == guess)
        if (!done) {
            println "Enter a number between $lower and $upper"
        }

        !done
    }
    def play(nextGuess) {
        if (nextGuess <= guess) {
            lower = [lower, nextGuess].max()
        }
        if (nextGuess >= guess) {
            upper = [upper, nextGuess].min()
        }
    }
}

def guessFactory = [messages: GuessGameMessages, control: GuessGameControl, converter: GuessGameInputConverter]
def twoupFactory = [messages: TwoupMessages, control: TwoupControl, converter: TwoupInputConverter]

class GameFactory {
    def static factory
    def static getMessages() { return factory.messages.newInstance() }
    def static getControl() { return factory.control.newInstance() }
    def static getConverter() { return factory.converter.newInstance() }
}

GameFactory.factory = twoupFactory
def messages = GameFactory.messages
def control = GameFactory.control
def converter = GameFactory.converter
println messages.welcome
def reader = new BufferedReader(new InputStreamReader(System.in))
while (control.moreTurns()) {
    def input = reader.readLine().trim()
    control.play(converter.convert(input))
}
println messages.done

Welcome to the twoup game, you start with $1000
You have 1000, how much would you like to bet?
300
Draw
You have 1000, how much would you like to bet?
700
You win
You have 1700, how much would you like to bet?
1700
You lose
Sorry, you have no money left, goodbye

Welcome to the guessing game, my secret number is between 1 and 100
Enter a number between 1 and 100
75
Enter a number between 1 and 75
35
Enter a number between 1 and 35
15
Enter a number between 1 and 15
5
Enter a number between 5 and 15
10
Correct

class SquarePeg {
    def width
}

class RoundPeg {
    def radius
}

class RoundHole {
    def radius
    def pegFits(peg) {
        peg.radius <= radius
    }
    String toString() { "RoundHole with radius $radius" }
}

class SquarePegAdapter {
    def peg
    def getRadius() {
        Math.sqrt(((peg.width / 2) ** 2) * 2)
    }
    String toString() {
        "SquarePegAdapter with peg width $peg.width (and notional radius $radius)"
    }
}

def hole = new RoundHole(radius: 4.0)
(4..7).each { w ->
    def peg = new SquarePegAdapter(peg: new SquarePeg(width: w))
    if (hole.pegFits(peg)) {
        println "peg $peg fits in hole $hole"
    } else {
        println "peg $peg does not fit in hole $hole"
    }
}

peg SquarePegAdapter with peg width 4 (and notional radius 2.8284271247461903) fits in hole RoundHole with radius 4.0
peg SquarePegAdapter with peg width 5 (and notional radius 3.5355339059327378) fits in hole RoundHole with radius 4.0
peg SquarePegAdapter with peg width 6 (and notional radius 4.242640687119285) does not fit in hole RoundHole with radius 4.0
peg SquarePegAdapter with peg width 7 (and notional radius 4.949747468305833) does not fit in hole RoundHole with radius 4.0

class SquarePeg {
    def width
}

class RoundPeg {
    def radius
}

class RoundHole {
    def radius
    def pegFits(peg) {
        peg.radius <= radius
    }
    String toString() { "RoundHole with radius $radius" }
}

class SquarePegAdapter extends SquarePeg {
    def getRadius() {
        Math.sqrt(((width / 2) ** 2) * 2)
    }
    String toString() {
        "SquarePegAdapter with width $width (and notional radius $radius)"
    }
}

def hole = new RoundHole(radius: 4.0)
(4..7).each { w ->
    def peg = new SquarePegAdapter(width: w)
    if (hole.pegFits(peg)) {
        println "peg $peg fits in hole $hole"
    } else {
        println "peg $peg does not fit in hole $hole"
    }
}

peg SquarePegAdapter with width 4 (and notional radius 2.8284271247461903) fits in hole RoundHole with radius 4.0
peg SquarePegAdapter with width 5 (and notional radius 3.5355339059327378) fits in hole RoundHole with radius 4.0
peg SquarePegAdapter with width 6 (and notional radius 4.242640687119285) does not fit in hole RoundHole with radius 4.0
peg SquarePegAdapter with width 7 (and notional radius 4.949747468305833) does not fit in hole RoundHole with radius 4.0

interface RoundThing {
    def getRadius()
}

def adapter = {
    p -> [getRadius: { Math.sqrt(((p.width / 2) ** 2) * 2) }] as RoundThing
}

def peg = new SquarePeg(width: 4)
if (hole.pegFits(adapter(peg))) {
    // ... as before
}

def peg = new SquarePeg(width: 4)
peg.metaClass.radius = Math.sqrt(((peg.width / 2) ** 2) * 2)

class NullChecker {
    static check(name, arg) {
        if (arg == null) {
            throw new IllegalArgumentException(name + ' is null')
        }
    }
}

void doStuff(String name, Object value) {
    NullChecker.check('name', name)
    NullChecker.check('value', value)
    // do stuff
}

void doStuff(String name, Object value) {
    assert name != null, 'name should not be null'
    assert value != null, 'value should not be null'
    // do stuff
}

class NumberChecker {
    static final String NUMBER_PATTERN = "\\\\d+(\\\\.\\\\d+(E-?\\\\d+)?)?"
    static isNumber(str) {
        if (!str ==~ NUMBER_PATTERN) {
            throw new IllegalArgumentException("Argument '$str' must be a number")
        }
    }
    static isNotZero(number) {
        if (number == 0) {
            throw new IllegalArgumentException('Argument must not be 0')
        }
    }
}

def stringDivide(String dividendStr, String divisorStr) {
    NumberChecker.isNumber(dividendStr)
    NumberChecker.isNumber(divisorStr)
    def dividend = dividendStr.toDouble()
    def divisor = divisorStr.toDouble()
    NumberChecker.isNotZero(divisor)
    dividend / divisor
}

println stringDivide('1.2E2', '3.0')
// => 40.0

def stringDivide(String dividendStr, String divisorStr) {
    assert dividendStr =~ NumberChecker.NUMBER_PATTERN
    assert divisorStr =~ NumberChecker.NUMBER_PATTERN
    def dividend = dividendStr.toDouble()
    def divisor = divisorStr.toDouble()
    assert divisor != 0, 'Divisor must not be 0'
    dividend / divisor
}

class UnixLister {
    private nextInLine
    UnixLister(next) { nextInLine = next }
    def listFiles(dir) {
        if (System.getProperty('os.name') == 'Linux') {
            println "ls $dir".execute().text
        } else {
            nextInLine.listFiles(dir)
        }
    }
}

class WindowsLister {
    private nextInLine
    WindowsLister(next) { nextInLine = next }
    def listFiles(dir) {
        if (System.getProperty('os.name').startsWith('Windows')) {
            println "cmd.exe /c dir $dir".execute().text
        } else {
            nextInLine.listFiles(dir)
        }
    }
}

class DefaultLister {
    def listFiles(dir) {
        new File(dir).eachFile { f -> println f }
    }
}

def lister = new UnixLister(new WindowsLister(new DefaultLister()))

lister.listFiles('Downloads')

String unixListFiles(dir) {
    if (System.getProperty('os.name') == 'Linux') {
        "ls $dir".execute().text
    }
}

String windowsListFiles(dir) {
    if (System.getProperty('os.name').startsWith('Windows')) {
        "cmd.exe /c dir $dir".execute().text
    }
}

String defaultListFiles(dir) {
    new File(dir).listFiles().collect{ f -> f.name }.join('\\n')
}

def dir = 'Downloads'
println unixListFiles(dir) ?: windowsListFiles(dir) ?: defaultListFiles(dir)

String listFiles(dir) {
    switch(dir) {
    case { System.getProperty('os.name') == 'Linux' }:
        return "ls $dir".execute().text
    case { System.getProperty('os.name').startsWith('Windows') }:
        return "cmd.exe /c dir $dir".execute().text
    default:
        new File(dir).listFiles().collect{ f -> f.name }.join('\\n')
    }
}

println listFiles('Downloads')

Optional<String> unixListFiles(String dir) {
    Optional.ofNullable(dir)
        .filter(d -> System.getProperty('os.name') == 'Linux')
        .map(d -> "ls $d".execute().text)
}

Optional<String> windowsListFiles(String dir) {
    Optional.ofNullable(dir)
        .filter(d -> System.getProperty('os.name').startsWith('Windows'))
        .map(d -> "cmd.exe /c dir $d".execute().text)
}

Optional<String> defaultListFiles(String dir) {
    Optional.ofNullable(dir)
        .map(d -> new File(d).listFiles().collect{ f -> f.name }.join('\\n'))
}

def dir = 'Downloads'
def handlers = [this::unixListFiles, this::windowsListFiles, this::defaultListFiles]
println handlers.stream()
    .map(f -> f(dir))
    .filter(Optional::isPresent)
    .map(Optional::get)
    .findFirst()
    .get()

import static Math.PI as π
abstract class Shape {
    String name
}
class Polygon extends Shape {
    String name
    double lengthSide
    int numSides
}
class Circle extends Shape {
    double radius
}

class CircleAreaCalculator {
    def next
    def area(shape) {
        if (shape instanceof Circle) {            (1)
            return shape.radius ** 2 * π
        } else {
            next.area(shape)
        }
    }
}
class SquareAreaCalculator {
    def next
    def area(shape) {
        if (shape instanceof Polygon && shape.numSides == 4) {      (1)
            return shape.lengthSide ** 2
        } else {
            next.area(shape)
        }
    }
}
class DefaultAreaCalculator {
    def area(shape) {
        throw new IllegalArgumentException("Don't know how to calculate area for $shape")
    }
}

def chain = new CircleAreaCalculator(next: new SquareAreaCalculator(next: new DefaultAreaCalculator()))
def shapes = [
    new Circle(name: 'Circle', radius: 5.0),
    new Polygon(name: 'Square', lengthSide: 10.0, numSides: 4)
]
shapes.each { println chain.area(it) }

// ...
class Square extends Polygon {
    // ...
}

double area(Circle c) {
    c.radius ** 2 * π
}

double area(Square s) {
    s.lengthSide ** 2
}

def shapes = [
    new Circle(radius: 5.0),
    new Square(lengthSide: 10.0, numSides: 4)
]
shapes.each { println area(it) }

import static Math.PI as π
interface Shape {
    double area()
}
abstract class Polygon implements Shape {
    double lengthSide
    int numSides
    abstract double area()
}
class Circle implements Shape {
    double radius
    double area() {
        radius ** 2 * π
    }
}
class Square extends Polygon {
    // ...
    double area() {
        lengthSide ** 2
    }
}

def shapes = [
    new Circle(radius: 5.0),
    new Square(lengthSide: 10.0, numSides: 4)
]
shapes.each { println it.area() }

interface Command {
    void execute()
}

// invoker class
class Switch {
    private final Map<String, Command> commandMap = new HashMap<>()

    void register(String commandName, Command command) {
        commandMap[commandName] = command
    }

    void execute(String commandName) {
        Command command = commandMap[commandName]
        if (!command) {
            throw new IllegalStateException("no command registered for " + commandName)
        }
        command.execute()
    }
}

// receiver class
class Light {
    void turnOn() {
        println "The light is on"
    }

    void turnOff() {
        println "The light is off"
    }
}

class SwitchOnCommand implements Command {
    Light light

    @Override // Command
    void execute() {
        light.turnOn()
    }
}

class SwitchOffCommand implements Command {
    Light light

    @Override // Command
    void execute() {
        light.turnOff()
    }
}

Light lamp = new Light()
Command switchOn = new SwitchOnCommand(light: lamp)
Command switchOff = new SwitchOffCommand(light: lamp)

Switch mySwitch = new Switch()
mySwitch.register("on", switchOn)
mySwitch.register("off", switchOff)

mySwitch.execute("on")
mySwitch.execute("off")

interface Command {
    void execute()
}

// invoker class
class Switch {
    private final Map<String, Command> commandMap = [:]

    void register(String commandName, Command command) {
        commandMap[commandName] = command
    }

    void execute(String commandName) {
        Command command = commandMap[commandName]
        if (!command) {
            throw new IllegalStateException("no command registered for $commandName")
        }
        command.execute()
    }
}

// receiver class
class Light {
    void turnOn() {
        println 'The light is on'
    }

    void turnOff() {
        println 'The light is off'
    }
}

Light lamp = new Light()

Switch mySwitch = new Switch()
mySwitch.register("on", lamp.&turnOn)       (1)
mySwitch.register("off", lamp.&turnOff)     (1)

mySwitch.execute("on")
mySwitch.execute("off")

class Light {
    void turnOn() {
        println 'The light is on'
    }

    void turnOff() {
        println 'The light is off'
    }
}

class Door {
    static void unlock() {
        println 'The door is unlocked'
    }
}

Light lamp = new Light()
Map<String, Runnable> mySwitch = [
    on: lamp::turnOn,
    off: lamp::turnOff,
    unlock: Door::unlock
]

mySwitch.on()
mySwitch.off()
mySwitch.unlock()

The light is on
The light is off
The door is unlocked

// ...
List<Runnable> tasks = [lamp::turnOn, lamp::turnOff, Door::unlock]
tasks.each{ it.run() }

abstract class Component {
    def name
    def toString(indent) {
        ("-" * indent) + name
    }
}

class Composite extends Component {
    private children = []
    def toString(indent) {
        def s = super.toString(indent)
        children.each { child ->
            s += "\\n" + child.toString(indent + 1)
        }
        s
    }
    def leftShift(component) {
        children << component
    }
}

class Leaf extends Component { }

def root = new Composite(name: "root")
root << new Leaf(name: "leaf A")
def comp = new Composite(name: "comp B")
root << comp
root << new Leaf(name: "leaf C")
comp << new Leaf(name: "leaf B1")
comp << new Leaf(name: "leaf B2")
println root.toString(0)

root
-leaf A
-comp B
--leaf B1
--leaf B2
-leaf C

class Logger {
    def log(String message) {
        println message
    }
}

class TimeStampingLogger extends Logger {
    private Logger logger
    TimeStampingLogger(logger) {
        this.logger = logger
    }
    def log(String message) {
        def now = Calendar.instance
        logger.log("$now.time: $message")
    }
}

class UpperLogger extends Logger {
    private Logger logger
    UpperLogger(logger) {
        this.logger = logger
    }
    def log(String message) {
        logger.log(message.toUpperCase())
    }
}

def logger = new UpperLogger(new TimeStampingLogger(new Logger()))
logger.log("G'day Mate")
// => Tue May 22 07:13:50 EST 2007: G'DAY MATE

logger = new TimeStampingLogger(new UpperLogger(new Logger()))
logger.log('Hi There')
// => TUE MAY 22 07:13:50 EST 2007: HI THERE

class DecoratingLogger {
    def decoration = Closure.IDENTITY

    def log(String message) {
        println decoration(message)
    }
}

def upper = { it.toUpperCase() }
def stamp = { "$Calendar.instance.time: $it" }
def logger = new DecoratingLogger(decoration: stamp << upper)
logger.log("G'day Mate")
// Sat Aug 29 15:28:29 AEST 2020: G'DAY MATE

import java.util.function.Function

class DecoratingLogger {
    Function<String, String> decoration = Function.identity()

    def log(String message) {
        println decoration.apply(message)
    }
}

Function<String, String> upper = s -> s.toUpperCase()
Function<String, String> stamp = s -> "$Calendar.instance.time: $s"
def logger = new DecoratingLogger(decoration: upper.andThen(stamp))
logger.log("G'day Mate")
// => Sat Aug 29 15:38:28 AEST 2020: G'DAY MATE

class GenericLowerDecorator {
    private delegate
    GenericLowerDecorator(delegate) {
        this.delegate = delegate
    }
    def invokeMethod(String name, args) {
        def newargs = args.collect { arg ->
            if (arg instanceof String) {
                return arg.toLowerCase()
            } else {
                return arg
            }
        }
        delegate.invokeMethod(name, newargs)
    }
}

logger = new GenericLowerDecorator(new TimeStampingLogger(new Logger()))
logger.log('IMPORTANT Message')
// => Tue May 22 07:27:18 EST 2007: important message

// Can't mix and match Interface-Oriented and Generic decorators
// logger = new TimeStampingLogger(new GenericLowerDecorator(new Logger()))

// current mechanism to enable ExpandoMetaClass
GroovySystem.metaClassRegistry.metaClassCreationHandle = new ExpandoMetaClassCreationHandle()

def logger = new Logger()
logger.metaClass.log = { String m -> println 'message: ' + m.toUpperCase() }
logger.log('x')
// => message: X

class Calc {
    def add(a, b) { a + b }
}

class TracingDecorator {
    private delegate
    TracingDecorator(delegate) {
        this.delegate = delegate
    }
    def invokeMethod(String name, args) {
        println "Calling $name$args"
        def before = System.currentTimeMillis()
        def result = delegate.invokeMethod(name, args)
        println "Got $result in ${System.currentTimeMillis()-before} ms"
        result
    }
}

def tracedCalc = new TracingDecorator(new Calc())
assert 15 == tracedCalc.add(3, 12)

Calling add{3, 12}
Got 15 in 31 ms

class TimingInterceptor extends TracingInterceptor {
    private beforeTime
    def beforeInvoke(object, String methodName, Object[] arguments) {
        super.beforeInvoke(object, methodName, arguments)
        beforeTime = System.currentTimeMillis()
    }
    Object afterInvoke(Object object, String methodName, Object[] arguments, Object result) {
        super.afterInvoke(object, methodName, arguments, result)
        def duration = System.currentTimeMillis() - beforeTime
        writer.write("Duration: $duration ms\\n")
        writer.flush()
        result
    }
}

def proxy = ProxyMetaClass.getInstance(Calc)
proxy.interceptor = new TimingInterceptor()
proxy.use {
    assert 7 == new Calc().add(1, 6)
}

before Calc.ctor()
after  Calc.ctor()
Duration: 0 ms
before Calc.add(java.lang.Integer, java.lang.Integer)
after  Calc.add(java.lang.Integer, java.lang.Integer)
Duration: 2 ms

protected Sql getGroovySql() {
    final Connection con = session.connection()
    def invoker = { object, method, args ->
        if (method.name == "close") {
            log.debug("ignoring call to Connection.close() for use by groovy.sql.Sql")
        } else {
            log.trace("delegating $method")
            return con.invokeMethod(method.name, args)
        }
    } as InvocationHandler;
    def proxy = Proxy.newProxyInstance( getClass().getClassLoader(), [Connection] as Class[], invoker )
    return new Sql(proxy)
}

interface Calc {
    def add(a, b)
}

class CalcImpl implements Calc {
    def add(a, b) { a + b }
}

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns:lang="http://www.springframework.org/schema/lang"
	xsi:schemaLocation="
		http://www.springframework.org/schema/beans https://www.springframework.org/schema/beans/spring-beans.xsd
		http://www.springframework.org/schema/lang https://www.springframework.org/schema/lang/spring-lang.xsd">

    <bean id="performanceInterceptor" autowire="no"
          class="org.springframework.aop.interceptor.PerformanceMonitorInterceptor">
        <property name="loggerName" value="performance"/>
    </bean>
    <bean id="calc" class="util.CalcImpl"/>
    <bean class="org.springframework.aop.framework.autoproxy.BeanNameAutoProxyCreator">
        <property name="beanNames" value="calc"/>
        <property name="interceptorNames" value="performanceInterceptor"/>
    </bean>
</beans>

@Grab('org.springframework:spring-context:5.2.8.RELEASE')
import org.springframework.context.support.ClassPathXmlApplicationContext

def ctx = new ClassPathXmlApplicationContext('beans.xml')
def calc = ctx.getBean('calc')
println calc.add(3, 25)

21/05/2007 23:02:35 org.springframework.aop.interceptor.PerformanceMonitorInterceptor invokeUnderTrace
FINEST: StopWatch 'util.Calc.add': running time (millis) = 16

@Grab('org.codehaus.gpars:gpars:0.10')
import static groovyx.gpars.GParsPool.withPool

interface Document {
    void print()
    String getText()
}

class DocumentImpl implements Document {
    def document
    void print() { println document }
    String getText() { document }
}

def words(String text) {
    text.replaceAll('[^a-zA-Z]', ' ').trim().split("\\\\s+")*.toLowerCase()
}

def avgWordLength = {
    def words = words(it.text)
    sprintf "Avg Word Length: %4.2f", words*.size().sum() / words.size()
}
def modeWord = {
    def wordGroups = words(it.text).groupBy {it}.collectEntries { k, v -> [k, v.size()] }
    def maxSize = wordGroups*.value.max()
    def maxWords = wordGroups.findAll { it.value == maxSize }
    "Mode Word(s): ${maxWords*.key.join(', ')} ($maxSize occurrences)"
}
def wordCount = { d -> "Word Count: " + words(d.text).size() }

def asyncDecorator(Document d, Closure c) {
    ProxyGenerator.INSTANCE.instantiateDelegate([print: {
        withPool {
            def result = c.callAsync(d)
            d.print()
            println result.get()
        }
    }], [Document], d)
}

Document d = asyncDecorator(asyncDecorator(asyncDecorator(
        new DocumentImpl(document:"This is the file with the words in it\\n\\t\\nDo you see the words?\\n"),
//        new DocumentImpl(document: new File('AsyncDecorator.groovy').text),
        wordCount), modeWord), avgWordLength)
d.print()

class Delegator {
    private targetClass
    private delegate
    Delegator(targetClass, delegate) {
        this.targetClass = targetClass
        this.delegate = delegate
    }
    def delegate(String methodName) {
        delegate(methodName, methodName)
    }
    def delegate(String methodName, String asMethodName) {
        targetClass.metaClass."$asMethodName" = delegate.&"$methodName"
    }
    def delegateAll(String[] names) {
        names.each { delegate(it) }
    }
    def delegateAll(Map names) {
        names.each { k, v -> delegate(k, v) }
    }
    def delegateAll() {
        delegate.class.methods*.name.each { delegate(it) }
    }
}

class Person {
    String name
}

class MortgageLender {
    def borrowAmount(amount) {
       "borrow \\$$amount"
    }
    def borrowFor(thing) {
       "buy \\$thing"
    }
}

def lender = new MortgageLender()

def delegator = new Delegator(Person, lender)

delegator.delegate 'borrowFor'
delegator.delegate 'borrowAmount', 'getMoney'

def p = new Person()

println p.borrowFor('present')   // => buy present
println p.getMoney(50)

delegator.delegateAll 'borrowFor', 'borrowAmount'

delegator.delegateAll()

delegator.delegateAll borrowAmount:'getMoney', borrowFor:'getThing'

class Person {
    def name
    @Delegate MortgageLender mortgageLender = new MortgageLender()
}

class MortgageLender {
    def borrowAmount(amount) {
       "borrow \\$$amount"
    }
    def borrowFor(thing) {
       "buy $thing"
    }
}

def p = new Person()

assert "buy present" == p.borrowFor('present')
assert "borrow \\$50" == p.borrowAmount(50)

class Boeing797 {
    def wingspan = '80.8 m'
    def capacity = 1000
    def speed = '1046 km/h'
    def range = '14400 km'
    // ...
}

class Airbus380 {
    def wingspan = '79.8 m'
    def capacity = 555
    def speed = '912 km/h'
    def range = '10370 km'
    // ...
}

class FlyweightFactory {
    static instances = [797: new Boeing797(), 380: new Airbus380()]
}

class Aircraft {
    private type         // intrinsic state
    private assetNumber  // extrinsic state
    private bought       // extrinsic state
    Aircraft(typeCode, assetNumber, bought) {
        type = FlyweightFactory.instances[typeCode]
        this.assetNumber = assetNumber
        this.bought = bought
    }
    def describe() {
        println """
        Asset Number: $assetNumber
        Capacity: $type.capacity people
        Speed: $type.speed
        Range: $type.range
        Bought: $bought
        """
    }
}

def fleet = [
    new Aircraft(380, 1001, '10-May-2007'),
    new Aircraft(380, 1002, '10-Nov-2007'),
    new Aircraft(797, 1003, '10-May-2008'),
    new Aircraft(797, 1004, '10-Nov-2008')
]

fleet.each { p -> p.describe() }

Asset Number: 1001
Capacity: 555 people
Speed: 912 km/h
Range: 10370 km
Bought: 10-May-2007

Asset Number: 1002
Capacity: 555 people
Speed: 912 km/h
Range: 10370 km
Bought: 10-Nov-2007

Asset Number: 1003
Capacity: 1000 people
Speed: 1046 km/h
Range: 14400 km
Bought: 10-May-2008

Asset Number: 1004
Capacity: 1000 people
Speed: 1046 km/h
Range: 14400 km
Bought: 10-Nov-2008

def f = new File('junk.txt')
f.withPrintWriter { pw ->
    pw.println(new Date())
    pw.println(this.class.name)
}
println f.size()
// => 42

f.eachLine { line ->
    println line
}
// =>
// Mon Jun 18 22:38:17 EST 2007
// RunPattern

def reader = f.newReader()
reader.splitEachLine(' ') { wordList ->
    println wordList
}
reader.close()
// =>
// [ "Mon", "Jun", "18", "22:38:17", "EST", "2007" ]
// [ "RunPattern" ]

def withListOfWordsForEachLine(File f, Closure c) {
    def r = f.newReader()
    try {
        r.splitEachLine(' ', c)
    } finally {
        r?.close()
    }
}

withListOfWordsForEachLine(f) { wordList ->
    println wordList
}
// =>
// [ "Mon", "Jun", "18", "22:38:17", "EST", "2007" ]
// [ "RunPattern" ]

def nums = 10..16
GParsPool.withPool {
    assert 91 == nums.injectParallel(0){ total, next -> total + next }
    assert 91 == nums.parallel.reduce(0, (total, next) -> total + next)
}

assert (1..10).average() == 5.5

assert (0..10).average() == 5

def avg = { a, b -> (a + b) / 2 }

assert 6 == avg(avg(10, 2), 6)
assert 7 == avg(10, avg(2, 6))

def nums = 1..10
def total = nums.sum()
def avg = total / nums.size()
assert avg == 5.5

withPool {
    assert 5.5 == nums.sumParallel() / nums.size()
}

def holder = nums
    .collect{ [it, 1] }
    .inject{ a, b -> [a[0] + b[0], a[1] + b[1]] }
def avg = holder[0] / holder[1]
assert avg == 5.5

class AverageHolder {
    int total
    int count
    AverageHolder plus(AverageHolder other) {
        return new AverageHolder(total: total + other.total,
                                 count: count + other.count)
    }
    static final AverageHolder ZERO =
        new AverageHolder(total: 0, count: 0)
}

def asHolder = {
    it instanceof Integer ? new AverageHolder(total: it, count : 1) : it
}
def pairwiseAggregate = { aggregate, next ->
    asHolder(aggregate) + asHolder(next)
}
withPool {
    def holder = nums.injectParallel(AverageHolder.ZERO, pairwiseAggregate)
    def avg = holder.with{ total / count }
    assert avg == 5.5
}

class Job {
    def salary
}

class Person {
    def name
    def Job job
}

def people = [
    new Person(name: 'Tom', job: new Job(salary: 1000)),
    new Person(name: 'Dick', job: new Job(salary: 1200)),
]

def biggestSalary = people.collect { p -> p.job.salary }.max()
println biggestSalary

people << new Person(name: 'Harry')

class NullJob extends Job { def salary = 0 }

people << new Person(name: 'Harry', job: new NullJob())
biggestSalary = people.collect { p -> p.job.salary }.max()
println biggestSalary

people << new Person(name:'Harry')
biggestSalary = people.collect { p -> p.job?.salary }.max()
println biggestSalary

class NullHandlingTree {
    def left, right, value

    def size() {
        1 + (left ? left.size() : 0) + (right ? right.size() : 0)
    }

    def sum() {
       value + (left ? left.sum() : 0) + (right ? right.sum() : 0)
    }

    def product() {
       value * (left ? left.product() : 1) * (right ? right.product() : 1)
    }
}

def root = new NullHandlingTree(
    value: 2,
    left: new NullHandlingTree(
        value: 3,
        right: new NullHandlingTree(value: 4),
        left: new NullHandlingTree(value: 5)
    )
)

println root.size()
println root.sum()
println root.product()

class Tree {
    def left = new NullTree(), right = new NullTree(), value

    def size() {
        1 + left.size() + right.size()
    }

    def sum() {
       value + left.sum() + right.sum()
    }

    def product() {
       value * left.product() * right.product()
    }
}

class NullTree {
    def size() { 0 }
    def sum() { 0 }
    def product() { 1 }
}

def root = new Tree(
    value: 2,
    left: new Tree(
        value: 3,
        right: new Tree(value: 4),
        left: new Tree(value: 5)
    )
)

println root.size()
println root.sum()
println root.product()

4
14
120

interface Observer {
    void update(message)
}

class Subject {
    private List observers = []
    void register(observer) {
        observers << observer
    }
    void unregister(observer) {
        observers -= observer
    }
    void notifyAll(message) {
        observers.each{ it.update(message) }
    }
}

class ConcreteObserver1 implements Observer {
    def messages = []
    void update(message) {
        messages << message
    }
}

class ConcreteObserver2 implements Observer {
    def messages = []
    void update(message) {
        messages << message.toUpperCase()
    }
}

def o1a = new ConcreteObserver1()
def o1b = new ConcreteObserver1()
def o2 = new ConcreteObserver2()
def observers = [o1a, o1b, o2]
new Subject().with {
    register(o1a)
    register(o2)
    notifyAll('one')
}
new Subject().with {
    register(o1b)
    register(o2)
    notifyAll('two')
}
def expected = [['one'], ['two'], ['ONE', 'TWO']]
assert observers*.messages == expected

interface Observer {
    void update(message)
}

class Subject {
    private List observers = []
    void register(Observer observer) {
        observers << observer
    }
    void unregister(observer) {
        observers -= observer
    }
    void notifyAll(message) {
        observers.each{ it.update(message) }
    }
}

def messages1a = [], messages1b = [], messages2 = []
def o2 = { messages2 << it.toUpperCase() }
new Subject().with {
    register{ messages1a << it }
    register(o2)
    notifyAll('one')
}
new Subject().with {
    register{ messages1b << it }
    register(o2)
    notifyAll('two')
}
def expected = [['one'], ['two'], ['ONE', 'TWO']]
assert [messages1a, messages1b, messages2] == expected

import java.util.function.Consumer

class Subject {
    private List<Consumer> observers = []
    void register(Consumer observer) {
        observers << observer
    }
    void unregister(observer) {
        observers -= observer
    }
    void notifyAll(message) {
        observers.each{ it.accept(message) }
    }
}

def messages1a = [], messages1b = [], messages2 = []
def o2 = { messages2 << it.toUpperCase() }
new Subject().with {
    register(s -> messages1a << s)
    register(s -> messages2 << s.toUpperCase())
    notifyAll('one')
}
new Subject().with {
    register(s -> messages1b << s)
    register(s -> messages2 << s.toUpperCase())
    notifyAll('two')
}
def expected = [['one'], ['two'], ['ONE', 'TWO']]
assert [messages1a, messages1b, messages2] == expected

import groovy.beans.*
import java.beans.*

class PersonBean {
    @Bindable String first
    @Bindable String last
    @Vetoable Integer age
}

def messages = [:].withDefault{[]}
new PersonBean().with {
    addPropertyChangeListener{ PropertyChangeEvent ev ->
        messages[ev.propertyName] << "prop: $ev.newValue"
    }
    addVetoableChangeListener{ PropertyChangeEvent ev ->
        def name = ev.propertyName
        if (name == 'age' && ev.newValue > 40)
            throw new PropertyVetoException()
        messages[name] << "veto: $ev.newValue"
    }
    first = 'John'
    age = 35
    last = 'Smith'
    first = 'Jane'
    age = 42
}

def expected = [
    first:['prop: John', 'prop: Jane'],
    age:['veto: 35'],
    last:['prop: Smith']
]
assert messages == expected

class EnhancedInteger {
    static boolean greaterThanAll(Integer self, Object[] others) {
        greaterThanAll(self, others)
    }
    static boolean greaterThanAll(Integer self, others) {
        others.every { self > it }
    }
}

use(EnhancedInteger) {
    assert 4.greaterThanAll(1, 2, 3)
    assert !5.greaterThanAll(2, 4, 6)
    assert 5.greaterThanAll(-4..4)
    assert 5.greaterThanAll([])
    assert !5.greaterThanAll([4, 5])
}

class AccumulatorProxy {
    def accumulate(args) {
        def result
        def s = new Socket("localhost", 54321)
        s.withObjectStreams { ois, oos ->
            oos << args
            result = ois.readObject()
        }
        s.close()
        return result
    }
}

println new AccumulatorProxy().accumulate([1, 2, 3, 4, 5, 6, 7, 8, 9, 10])
// => 55

class Accumulator {
    def accumulate(args) {
        args.inject(0) { total, arg -> total += arg }
    }
}

def port = 54321
def accumulator = new Accumulator()
def server = new ServerSocket(port)
println "Starting server on port $port"
while(true) {
    server.accept() { socket ->
        socket.withObjectStreams { ois, oos ->
            def args = ois.readObject()
            oos << accumulator.accumulate(args)
        }
    }
}

class VoteCollector {
    def votes = 0
    private static final INSTANCE = new VoteCollector()
    static getInstance() { return INSTANCE }
    private VoteCollector() { }
    def display() { println "Collector:${hashCode()}, Votes:$votes" }
}

def collector = VoteCollector.instance
collector.display()
collector.votes++
collector = null

Thread.start{
    def collector2 = VoteCollector.instance
    collector2.display()
    collector2.votes++
    collector2 = null
}.join()

def collector3 = VoteCollector.instance
collector3.display()

Collector:15959960, Votes:0
Collector:15959960, Votes:1
Collector:15959960, Votes:2

class Calculator {
    private total = 0
    def add(a, b) { total++; a + b }
    def getTotalCalculations() { 'Total Calculations: ' + total }
    String toString() { 'Calc: ' + hashCode() }
}

class Client {
    def calc = new Calculator()
    def executeCalc(a, b) { calc.add(a, b) }
    String toString() { 'Client: ' + hashCode() }
}

class CalculatorMetaClass extends MetaClassImpl {
    private static final INSTANCE = new Calculator()
    CalculatorMetaClass() { super(Calculator) }
    def invokeConstructor(Object[] arguments) { return INSTANCE }
}

def registry = GroovySystem.metaClassRegistry
registry.setMetaClass(Calculator, new CalculatorMetaClass())

def client = new Client()
assert 3 == client.executeCalc(1, 2)
println "$client, $client.calc, $client.calc.totalCalculations"

client = new Client()
assert 4 == client.executeCalc(2, 2)
println "$client, $client.calc, $client.calc.totalCalculations"

Client: 7306473, Calc: 24230857, Total Calculations: 1
Client: 31436753, Calc: 24230857, Total Calculations: 2

@Grapes([@Grab('aopalliance:aopalliance:1.0'), @Grab('com.google.code.guice:guice:1.0')])
import com.google.inject.*

interface Calculator {
    def add(a, b)
}

class CalculatorImpl implements Calculator {
    private total = 0
    def add(a, b) { total++; a + b }
    def getTotalCalculations() { 'Total Calculations: ' + total }
    String toString() { 'Calc: ' + hashCode() }
}

class Client {
    @Inject Calculator calc
    def executeCalc(a, b) { calc.add(a, b) }
    String toString() { 'Client: ' + hashCode() }
}

def injector = Guice.createInjector (
    [configure: { binding ->
        binding.bind(Calculator)
               .to(CalculatorImpl)
               .asEagerSingleton() } ] as Module
)

def client = injector.getInstance(Client)
assert 3 == client.executeCalc(1, 2)
println "$client, $client.calc, $client.calc.totalCalculations"

client = injector.getInstance(Client)
assert 4 == client.executeCalc(2, 2)
println "$client, $client.calc, $client.calc.totalCalculations"

@Grapes([@Grab('aopalliance:aopalliance:1.0'), @Grab('com.google.code.guice:guice:1.0')])
import com.google.inject.*

@ImplementedBy(CalculatorImpl)
interface Calculator {
    // as before ...
}

@Singleton
class CalculatorImpl implements Calculator {
    // as before ...
}

class Client {
    // as before ...
}

def injector = Guice.createInjector()

// ...

Client: 8897128, Calc: 17431955, Total Calculations: 1
Client: 21145613, Calc: 17431955, Total Calculations: 2

@Grapes([@Grab('org.springframework:spring-core:5.2.8.RELEASE'), @Grab('org.springframework:spring-beans:5.2.8.RELEASE')])
import org.springframework.beans.factory.support.*

interface Calculator {
    def add(a, b)
}

class CalculatorImpl implements Calculator {
    private total = 0
    def add(a, b) { total++; a + b }
    def getTotalCalculations() { 'Total Calculations: ' + total }
    String toString() { 'Calc: ' + hashCode() }
}

class Client {
    Client(Calculator calc) { this.calc = calc }
    def calc
    def executeCalc(a, b) { calc.add(a, b) }
    String toString() { 'Client: ' + hashCode() }
}

// Here we 'wire' up our dependencies through the API. Alternatively,
// we could use XML-based configuration or the Grails Bean Builder DSL.
def factory = new DefaultListableBeanFactory()
factory.registerBeanDefinition('calc', new RootBeanDefinition(CalculatorImpl))
def beanDef = new RootBeanDefinition(Client, false)
beanDef.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_AUTODETECT)
factory.registerBeanDefinition('client', beanDef)

def client = factory.getBean('client')
assert 3 == client.executeCalc(1, 2)
println "$client, $client.calc, $client.calc.totalCalculations"

client = factory.getBean('client')
assert 4 == client.executeCalc(2, 2)
println "$client, $client.calc, $client.calc.totalCalculations"

Client: 29418586, Calc: 10580099, Total Calculations: 1
Client: 14800362, Calc: 10580099, Total Calculations: 2

class Client {
    def context = new Context()
    def connect() {
        context.state.connect()
    }
    def disconnect() {
        context.state.disconnect()
    }
    def send_message(message) {
        context.state.send_message(message)
    }
    def receive_message() {
        context.state.receive_message()
    }
}

class Context {
    def state = new Offline(this)
}

class ClientState {
    def context
    ClientState(context) {
        this.context = context
        inform()
    }
}

class Offline extends ClientState {
    Offline(context) {
        super(context)
    }
    def inform() {
        println "offline"
    }
    def connect() {
        context.state = new Online(context)
    }
    def disconnect() {
        println "error: not connected"
    }
    def send_message(message) {
        println "error: not connected"
    }
    def receive_message() {
        println "error: not connected"
    }
}

class Online extends ClientState {
    Online(context) {
        super(context)
    }
    def inform() {
        println "connected"
    }
    def connect() {
        println "error: already connected"
    }
    def disconnect() {
        context.state = new Offline(context)
    }
    def send_message(message) {
        println "\"$message\" sent"
    }
    def receive_message() {
        println "message received"
    }
}

client = new Client()
client.send_message("Hello")
client.connect()
client.send_message("Hello")
client.connect()
client.receive_message()
client.disconnect()

offline
error: not connected
connected
"Hello" sent
error: already connected
message received
offline

interface State {
    def connect()
    def disconnect()
    def send_message(message)
    def receive_message()
}

class Client implements State {
  // ... as before ...
}

class Online implements State {
  // ... as before ...
}

class Offline implements State {
  // ... as before ...
}

abstract class InstanceProvider {
    static def registry = GroovySystem.metaClassRegistry
    static def create(objectClass, param) {
        registry.getMetaClass(objectClass).invokeConstructor([param] as Object[])
    }
}

abstract class Context {
    private context
    protected setContext(context) {
        this.context = context
    }
    def invokeMethod(String name, Object arg) {
        context.invokeMethod(name, arg)
    }
    def startFrom(initialState) {
        setContext(InstanceProvider.create(initialState, this))
    }
}

abstract class State {
    private client

    State(client) { this.client = client }

    def transitionTo(nextState) {
        client.setContext(InstanceProvider.create(nextState, client))
    }
}

class Client extends Context {
    Client() {
        startFrom(Offline)
    }
}

class Offline extends State {
    Offline(client) {
        super(client)
        println "offline"
    }
    def connect() {
        transitionTo(Online)
    }
    def disconnect() {
        println "error: not connected"
    }
    def send_message(message) {
        println "error: not connected"
    }
    def receive_message() {
        println "error: not connected"
    }
}

class Online extends State {
    Online(client) {
        super(client)
        println "connected"
    }
    def connect() {
        println "error: already connected"
    }
    def disconnect() {
        transitionTo(Offline)
    }
    def send_message(message) {
        println "\"$message\" sent"
    }
    def receive_message() {
        println "message received"
    }
}

client = new Client()
client.send_message("Hello")
client.connect()
client.send_message("Hello")
client.connect()
client.receive_message()
client.disconnect()

class Grammar {
    def fsm

    def event
    def fromState
    def toState

    Grammar(a_fsm) {
        fsm = a_fsm
    }

    def on(a_event) {
        event = a_event
        this
    }

    def on(a_event, a_transitioner) {
        on(a_event)
        a_transitioner.delegate = this
        a_transitioner.call()
        this
    }

    def from(a_fromState) {
        fromState = a_fromState
        this
    }

    def to(a_toState) {
        assert a_toState, "Invalid toState: $a_toState"
        toState = a_toState
        fsm.registerTransition(this)
        this
    }

    def isValid() {
        event && fromState && toState
    }

    public String toString() {
        "$event: $fromState=>$toState"
    }
}

class FiniteStateMachine {
    def transitions = [:]

    def initialState
    def currentState

    FiniteStateMachine(a_initialState) {
        assert a_initialState, "You need to provide an initial state"
        initialState = a_initialState
        currentState = a_initialState
    }

    def record() {
        Grammar.newInstance(this)
    }

    def reset() {
        currentState = initialState
    }

    def isState(a_state) {
        currentState == a_state
    }

    def registerTransition(a_grammar) {
        assert a_grammar.isValid(), "Invalid transition ($a_grammar)"
        def transition
        def event = a_grammar.event
        def fromState = a_grammar.fromState
        def toState = a_grammar.toState

        if (!transitions[event]) {
            transitions[event] = [:]
        }

        transition = transitions[event]
        assert !transition[fromState], "Duplicate fromState $fromState for transition $a_grammar"
        transition[fromState] = toState
    }

    def fire(a_event) {
        assert currentState, "Invalid current state '$currentState': passed into constructor"
        assert transitions.containsKey(a_event), "Invalid event '$a_event', should be one of ${transitions.keySet()}"
        def transition = transitions[a_event]
        def nextState = transition[currentState]
        assert nextState, "There is no transition from '$currentState' to any other state"
        currentState = nextState
        currentState
    }
}

class StatePatternDslTest extends GroovyTestCase {
    private fsm

    protected void setUp() {
        fsm = FiniteStateMachine.newInstance('offline')
        def recorder = fsm.record()
        recorder.on('connect').from('offline').to('online')
        recorder.on('disconnect').from('online').to('offline')
        recorder.on('send_message').from('online').to('online')
        recorder.on('receive_message').from('online').to('online')
    }

    void testInitialState() {
        assert fsm.isState('offline')
    }

    void testOfflineState() {
        shouldFail{
            fsm.fire('send_message')
        }
        shouldFail{
            fsm.fire('receive_message')
        }
        shouldFail{
            fsm.fire('disconnect')
        }
        assert 'online' == fsm.fire('connect')
    }

    void testOnlineState() {
        fsm.fire('connect')
        fsm.fire('send_message')
        fsm.fire('receive_message')
        shouldFail{
            fsm.fire('connect')
        }
        assert 'offline' == fsm.fire('disconnect')
    }
}

interface Calc {
    def execute(n, m)
}

class CalcByMult implements Calc {
    def execute(n, m) { n * m }
}

class CalcByManyAdds implements Calc {
    def execute(n, m) {
        def result = 0
        n.times{
            result += m
        }

        result
    }
}

def sampleData = [
    [3, 4, 12],
    [5, -5, -25]
]

Calc[] multiplicationStrategies = [
    new CalcByMult(),
    new CalcByManyAdds()
]

sampleData.each{ data ->
    multiplicationStrategies.each { calc ->
        assert data[2] == calc.execute(data[0], data[1])
    }
}

def multiplicationStrategies = [
    { n, m -> n * m },
    { n, m -> def result = 0; n.times{ result += m }; result }
]

def sampleData = [
    [3, 4, 12],
    [5, -5, -25]
]

sampleData.each{ data ->
    multiplicationStrategies.each { calc ->
        assert data[2] == calc(data[0], data[1])
    }
}

interface Calc {
    def execute(n, m)
}

List<Calc> multiplicationStrategies = [
    (n, m) -> n * m,
    (n, m) -> { def result = 0; n.times{ result += m }; result }
]

def sampleData = [
    [3, 4, 12],
    [5, -5, -25]
]

sampleData.each{ data ->
    multiplicationStrategies.each { calc ->
        assert data[2] == calc(data[0], data[1])
    }
}

import java.util.function.BiFunction

List<BiFunction<Integer, Integer, Integer>> multiplicationStrategies = [
    (n, m) -> n * m,
    (n, m) -> { def result = 0; n.times{ result += m }; result }
]

def sampleData = [
    [3, 4, 12],
    [5, -5, -25]
]

sampleData.each{ data ->
    multiplicationStrategies.each { calc ->
        assert data[2] == calc(data[0], data[1])
    }
}

abstract class Accumulator {
    protected initial
    abstract doAccumulate(total, v)
    def accumulate(values) {
        def total = initial
        values.each { v -> total = doAccumulate(total, v) }
        total
    }
}

class Sum extends Accumulator {
    def Sum() { initial = 0 }
    def doAccumulate(total, v) { total + v }
}

class Product extends Accumulator {
    def Product() { initial = 1 }
    def doAccumulate(total, v) { total * v }
}

assert 10 == new Sum().accumulate([1,2,3,4])
assert 24 == new Product().accumulate([1,2,3,4])

Closure addAll = { total, item -> total += item }
def accumulated = [1, 2, 3, 4].inject(0, addAll)
assert accumulated == 10

accumulated = [ "1", "2", "3", "4" ].inject("", addAll)
assert accumulated == "1234"

assert 24 == [1, 2, 3, 4].inject(1) { total, item -> total *= item }

assert 10 == [1, 2, 3, 4].stream().reduce(0, (l, r) -> l + r)
assert 24 == [1, 2, 3, 4].stream().reduce(1, (l, r) -> l * r)
assert '1234' == ['1', '2', '3', '4'].stream().reduce('', (l, r) -> l + r)

abstract class Shape { }

@ToString(includeNames=true)
class Rectangle extends Shape {
    def x, y, w, h

    Rectangle(x, y, w, h) {
        this.x = x; this.y = y; this.w = w; this.h = h
    }

    def union(rect) {
        if (!rect) return this
        def minx = [rect.x, x].min()
        def maxx = [rect.x + rect.w, x + w].max()
        def miny = [rect.y, y].min()
        def maxy = [rect.y + rect.h, y + h].max()
        new Rectangle(minx, miny, maxx - minx, maxy - miny)
    }

    def accept(visitor) {
        visitor.visit_rectangle(this)
    }
}

class Line extends Shape {
    def x1, y1, x2, y2

    Line(x1, y1, x2, y2) {
        this.x1 = x1; this.y1 = y1; this.x2 = x2; this.y2 = y2
    }

    def accept(visitor){
        visitor.visit_line(this)
    }
}

class Group extends Shape {
    def shapes = []
    def add(shape) { shapes += shape }
    def remove(shape) { shapes -= shape }
    def accept(visitor) {
        visitor.visit_group(this)
    }
}

class BoundingRectangleVisitor {
    def bounds

    def visit_rectangle(rectangle) {
        if (bounds)
            bounds = bounds.union(rectangle)
        else
            bounds = rectangle
    }

    def visit_line(line) {
        def line_bounds = new Rectangle([line.x1, line.x2].min(),
                                        [line.y1, line.y2].min(),
                                        line.x2 - line.y1,
                                        line.x2 - line.y2)
        if (bounds)
            bounds = bounds.union(line_bounds)
        else
            bounds = line_bounds
    }

    def visit_group(group) {
        group.shapes.each { shape -> shape.accept(this) }
    }
}

def group = new Group()
group.add(new Rectangle(100, 40, 10, 5))
group.add(new Rectangle(100, 70, 10, 5))
group.add(new Line(90, 30, 60, 5))
def visitor = new BoundingRectangleVisitor()
group.accept(visitor)
bounding_box = visitor.bounds
assert bounding_box.toString() == 'Rectangle(x:60, y:5, w:50, h:70)'

abstract class Shape {
    def accept(Closure yield) { yield(this) }
}

@ToString(includeNames=true)
class Rectangle extends Shape {
    def x, y, w, h
    def bounds() { this }
    def union(rect) {
        if (!rect) return this
        def minx = [ rect.x, x ].min()
        def maxx = [ rect.x + rect.w, x + w ].max()
        def miny = [ rect.y, y ].min()
        def maxy = [ rect.y + rect.h, y + h ].max()
        new Rectangle(x:minx, y:miny, w:maxx - minx, h:maxy - miny)
    }
}

class Line extends Shape {
    def x1, y1, x2, y2
    def bounds() {
        new Rectangle(x:[x1, x2].min(), y:[y1, y2].min(),
                      w:(x2 - x1).abs(), h:(y2 - y1).abs())
    }
}

class Group {
    def shapes = []
    def leftShift(shape) { shapes += shape }
    def accept(Closure yield) { shapes.each{it.accept(yield)} }
}

def group = new Group()
group << new Rectangle(x:100, y:40, w:10, h:5)
group << new Rectangle(x:100, y:70, w:10, h:5)
group << new Line(x1:90, y1:30, x2:60, y2:5)
def bounds
group.accept{ bounds = it.bounds().union(bounds) }
assert bounds.toString() == 'Rectangle(x:60, y:5, w:50, h:70)'

abstract class Shape {
    def accept(Function<Shape, Shape> yield) { yield.apply(this) }
}

@ToString(includeNames=true)
class Rectangle extends Shape {
    /* ... same as with Closures ... */
}

class Line extends Shape {
    /* ... same as with Closures ... */
}

class Group {
    def shapes = []
    def leftShift(shape) { shapes += shape }
    def accept(Function<Shape, Shape> yield) {
        shapes.stream().forEach(s -> s.accept(yield))
    }
}

def group = new Group()
group << new Rectangle(x:100, y:40, w:10, h:5)
group << new Rectangle(x:100, y:70, w:10, h:5)
group << new Line(x1:90, y1:30, x2:60, y2:5)
def bounds
group.accept(s -> { bounds = s.bounds().union(bounds) })
assert bounds.toString() == 'Rectangle(x:60, y:5, w:50, h:70)'

interface Visitor {
    void visit(NodeType1 n1)
    void visit(NodeType2 n2)
}

interface Visitable {
    void accept(Visitor visitor)
}

class NodeType1 implements Visitable {
    Visitable[] children = new Visitable[0]
    void accept(Visitor visitor) {
        visitor.visit(this)
        for(int i = 0; i < children.length; ++i) {
            children[i].accept(visitor)
        }
    }
}

class NodeType2 implements Visitable {
    Visitable[] children = new Visitable[0]
    void accept(Visitor visitor) {
        visitor.visit(this)
        for(int i = 0; i < children.length; ++i) {
            children[i].accept(visitor)
        }
    }
}

class NodeType1Counter implements Visitor {
    int count = 0
    void visit(NodeType1 n1) {
        count++
    }
    void visit(NodeType2 n2){}
}

NodeType1 root = new NodeType1()
root.children = new Visitable[]{new NodeType1(), new NodeType2()}

def counter = new NodeType1Counter()
root.accept(counter)
assert counter.count == 2