The Groovy Puzzlers – The Complete 01 and 02 Seasons

The Groovy Pz

The epic Groovy puzzlers!

Who's [email protected]/jbaruch

linkd.in/jbaruch

stackoverflow.com/users/402053/jbaruch

2

Developer who?

Developer who?

What Frog?

What Frog?

What Frog?

What Frog?

Frogs Groovy

Hosting Groovy on BintrayHosting Groovy on ArtifactoryBintray UI is GrailsArtifactory plugins are GroovyGradle and Grails plugins on Bintray

Frogs Groovy

Click and hackthe typing brothers

CURRENT JBNEXT - FRED2001 OracleWorld: Joshua Bloch, Neal Gafter14

BTW

CURRENT JBNEXT - FRED

The Car Show (1977-2012) Click and Clack, the Tappet Brothers - Tom and Ray Magliozzi

15

Two entertaining guys on stage


16

Ryan!

Two entertaining guys on stageFunny Puzzling questionsYou think and voteLots of T-shirts flying in the airOfficial twitter handle! groovypuzzlers


18

First rule of the puzzlers:No cheating!


19

First rule of the puzzlers:No cheating!Cdric?!


20

Consider the puzzlers correct as of 2.4.5

21


22

CURRENT FREDNEXT - FRED23

class Conference {def name; def year}

def gr = new Conference(name: 'Greach', year: 2014)

gr.each {println it}class=class Conferencename=Greachyear=2014 Conference@XXXXXX

Startup failure Greach 2014

CURRENT FREDNEXT - FRED

24

Not exactly iteration, is it?


25

Read the source, Luke.


26

Absolutely Groovy

CURRENT FREDNEXT - JB27

3NoSuchMethodError-3Execution Failure-3.abs()

CURRENT FREDNEXT - JB

28


29

Fix is simple(-3).abs()orint value = -3value.abs()


30

My idea prints nothing when I copy paste this code. What gives?


31

-333 and NullPointerException-3 and NullPointerExceptionPrintln for the rescue!println (-3).abs()


32


33

Delete all parentheses!Compiler will figure it out!


34

-3Caught: java.lang.NullPointerException: Cannot invoke method abs() on null objectjava.lang.NullPointerException: Cannot invoke method abs() on null objectat AbsolutelyGroovy.run(AbsolutelyGroovy.groovy:7)at com.intellij.rt.execution.application.AppMain.main(AppMain.java:134)println (-3).abs()


35

All problems in computer science can be solved by another pair of parentheses

John McCarthy, the inventor of LISP


36

Just Throw in some more parentheses!println ((-3).abs())orint value = -3println value.abs()


37

And the t-shirt goes to


38

'a'..'z'.each { println it }NoSuchMethodErrorzWont run

a b c . . . z

You knew it, right?('a'..'z').each { println it }



43

Max power

CURRENT JBNEXT - FRED44

Max powerList list = [56, '9', 74]def max = list.max { item -> (item < 50) ? item : null}println max


45

List list = [56, '9', 74]def max = list.max { item -> (item < 50) ? item : null}println maxClassCastException956null


46

Tricky, but I got it!>groovysh (('9' as Character) as Integer)===> 57


47

List list = [56, 57, 74]def max = list.max { item -> (item < 50) ? item : null}println max


48

Hmm, now they all null?!


49

ClassCastException956null

List list = [56, '9', 74]def max = list.max { item -> (item < 50) ? item : null}println max


50


51

What the hell happened?!def random = new Random()

def randomList = []0..10.each {randomList delegate.class.simpleName}.call())

class Ghostwriter { String book = '****** in Action, *** Edition'}

DierkGuillaumePaulCedricHamletErikJon.groovyGhostwriter Startup error DierkGuillaumePaulCedricHamletErikJon SimpleGroovyDoc


307


308

import org.codehaus.groovy.tools.groovydoc.SimpleGroovyDoc as delegate

// def delegate = new Ghostwriter()

println ({ -> delegate.class.name}.call())

/* class Ghostwriter { String book = '****** in Action, *** Edition'}*/

DierkGuillaumePaulCedricHamletErikJon.groovy

Startup error DierkGuillaumePaulCedricHamletErikJon SimpleGroovyDoc

CURRENT JBNEXT - FRED309

That explains *a lot*


310


311

1985


class CountDown { int counter = 10 }

CountDown finalCountDown() { def countDown = new CountDown() try { countDown.counter = --countDown.counter } catch (ignored) { println "That will never happen." countDown.counter = Integer.MIN_VALUE } finally { return countDown }}

println finalCountDown().counter


313


CountDown finalCountDown() { def countDown = new CountDown() try { countDown.counter = --countDown.counter } catch (ignored) { println "That will never happen." countDown.counter = Integer.MIN_VALUE } finally { return countDown }}


Startup failureThat will never happen.-2147483648910


314


315


CountDown finalCountDown() { def countDown = new CountDown() try { countDown.counter = --countDown.counter } catch (ignored) { ignored.printStackTrace() countDown.counter = Integer.MIN_VALUE } finally { return countDown }}

println finalCountDown().counterorg.codehaus.groovy.runtime.typehandling.GroovyCastException: Cannot cast object '9' with class 'java.lang.Integer' to class 'CountDown-2147483648


316

What the hell happened?!


317

Fix? Just use the answer.class CountDown { int counter = 10 }

CountDown finalCountDown() { def countDown = new CountDown() try { countDown.counter = --countDown.counter } catch (ignored) { println "That will never happen." countDown.counter = Integer.MIN_VALUE } finally { return countDown } 42}



318


How that even possible?!


320


321



322

And the t-shirts go to


323

Conclusions

Write readable codeComment neat tricksSometimes it is just a bugUse static code analysis (intellij IDEA!)Rtfm

Dont code like my brother

We have just started!(may end up in proper uniform)

Puzzlers? Gotchas? Fetal position inducing behavior?

puzzlers jfrog.com Groovypuzzlers

Jfrog always pays its debts

Positive feedback?Praise us on twitter groovypuzzlers Groovypuzzlers ryanvanderwerf jbaruch

Negative feeback?/dev/null

No, Thank you!

null10161.629The Final Countdown - fragmentEuropeTop Disco Hits vol. 1, track 179743.676

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The Groovy Puzzlers – The Complete 01 and 02 Seasons