Two hours of the Groovy Puzzlers as were presented at Groovy and Grails Austin Meetup! The video: https://www.youtube.com/watch?v=9qa1seKaRCU

2. linkd.in/jbaruch
stackoverflow.com/users/402053/jbaruch

16. 1. Two entertaining guys on stage

18. 1. Two entertaining guys on stage
2. Funny Puzzling questions
3. You think and vote
4. Lots of T-shirts flying in the air
5. Official twitter handle!
groovypuzzlers

20. Cédric?!

24. class Conference {def name; def year}
def gr = new Conference(name: 'Greach', year: 2014)
gr.each {println it}

28. -3.abs()

30. (-3).abs()
int value = -3
value.abs()

32. println (-3).abs()

35. -3
Caught: java.lang.NullPointerException: Cannot invoke method abs() on null
object
java.lang.NullPointerException: Cannot invoke method abs() on null object
at AbsolutelyGroovy.run(AbsolutelyGroovy.groovy:7)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:134)
println (-3).abs()

36. “All problems in computer science can be
solved by another pair of parentheses”
John McCarthy, the inventor of LISP

37. println ((-3).abs())
int value = -3
println value.abs()

40. 'a'..'z'.each { println it }
B. NoSuchMethodError
C. z
D. Won’t run
A. a
b
c
.
.
.
z

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

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

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

47. >groovysh (('9' as Character) as Integer)
===> 57

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

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

52. def random = new Random()
def randomList = []
0..10.each {randomList << random.nextInt()}
assert randomList.max{ null } == randomList[0]

55. def x = int
println x
if ((x = long)) {
println x
}
if (x = boolean ) {
println x
}

56. def x = int
println x
if ((x = long)) {
println x
}
if (x = boolean ) {
println x
}

62. def key = 'x'
def map = [key: 'treasure']
def value = map.get(key)
println value

63. def key = 'x'
def map = [key: 'treasure']
def value = map.get(key)
println value

66. 1.def map = [(key): 'treasure']
2.map.put(key, 'treasure')
3.map."$key" = 'treasure'
4.map[key] = 'treasure'

68. def map = [2: 'treasure']
def key = 2
def value = map."$key"
println value

69. def map = [2: 'treasure']
def key = 2
def value = map."$key"
println value

71. def map = [2: 'treasure']
println map.keySet().first().class.name
java.lang.Integer

74. @groovy.transform.InheritConstructors
class TreaayeMap extends HashMap {
}
TreaayeMap a = [5]
TreaayeMap b = [6]
println "${a.getClass()} ${a.equals(b)}"

78. TreaayeMap a = [5]

79. TreaayeMap a = [5]

80. TreaayeMap a = [5]

81. TreaayeMap a = [5]
@groovy.transform.InheritConstructors
class TreaayeMap extends HashMap {
}

82. TreaayeMap a = [5]
@groovy.transform.InheritConstructors
class TreaayeMap extends HashMap {
}
/**
* Constructs an empty <tt>HashMap</tt> with the specified initial
* capacity and the default load factor (0.75).
*
* @param initialCapacity the initial capacity.
* @throws IllegalArgumentException if the initial capacity is negative.
*/
public HashMap(int initialCapacity)

87. A. def beast = '6' * Math.PI
B. def beast = '6' * '3'
C. def beast = '667' – 1
D. def beast = '6' + '6' + 0 + 6

89. def beast = '6' * Math.PI

90. def beast = '6' * 3.1415926…

92. /**
* Repeat a String a certain number of times.
*
* @param self a String to be repeated
* @param factor the number of times the String should be repeated
* @return a String composed of a repetition
* @throws IllegalArgumentException if the number of repetitions is &lt; 0
* @since 1.0
*/
public static String multiply(String self, Number factor) {
int size = factor.intValue();
…
}

93. def beast = '6' * 3.1415926…

94. def beast = '6' * 3

95. B. def beast = '6' * '3'
C. def beast = '667' – 1
D. def beast = '6' + '6' + 0 + 6

96. B. def beast = '6' * '3'
C. def beast = '667' – 1
D. def beast = '6' + '6' + (0 + 6)

97. B. def beast = '6' * '3'
C. def beast = '667' – 1
D. def beast = '6' + '6' + (0 + 6)
Yup, I am
watching you!

100. class THERE_CAN_BE_ONLY_ONE { }
class MacLeod {
THERE_CAN_BE_ONLY_ONE getTHERE_CAN_BE_ONLY_ONE() {
Class clazz = THERE_CAN_BE_ONLY_ONE
return clazz.newInstance()
}
}
println new MacLeod().THERE_CAN_BE_ONLY_ONE

101. class THERE_CAN_BE_ONLY_ONE { }
class MacLeod {
THERE_CAN_BE_ONLY_ONE
getTHERE_CAN_BE_ONLY_ONE() {
Class clazz = THERE_CAN_BE_ONLY_ONE
return clazz.newInstance()
}
}
println new MacLeod().THERE_CAN_BE_ONLY_ONE
A. Won't start
B. No such property: THERE_CAN_BE_ONLY_ONE for class:
MacLeod
C. THERE_CAN_BE_ONLY_ONE@3d74bf60
D. Another Exception

103. A.MultipleCompilationErrorsException
B.StackOverflowError
C.NullPointerException
D.Yet Another Exception

105. class MacLeod {
THERE_CAN_BE_ONLY_ONE getTHERE_CAN_BE_ONLY_ONE() {
Class clazz = THERE_CAN_BE_ONLY_ONE
return clazz.newInstance()
}
}

106. class MacLeod {
THERE_CAN_BE_ONLY_ONE getTHERE_CAN_BE_ONLY_ONE() {
Class clazz = getTHERE_CAN_BE_ONLY_ONE()
return clazz.newInstance()
}
}

108. class MacLeod {
THERE_CAN_BE_ONLY_ONE getTHERE_CAN_BE_ONLY_ONE() {
Class<THERE_CAN_BE_ONLY_ONE> clazz =
THERE_CAN_BE_ONLY_ONE.class
return clazz.newInstance()
}
}

110. class MacLeod {
THERE_CAN_BE_ONLY_ONE getTHERE_CAN_BE_ONLY_ONE() {
Class<THERE_CAN_BE_ONLY_ONE> clazz =
getTHERE_CAN_BE_ONLY_ONE().class
return clazz.newInstance()
}
}

112. class MacLeod {
THERE_CAN_BE_ONLY_ONE getTHERE_CAN_BE_ONLY_ONE() {
Class<THERE_CAN_BE_ONLY_ONE> clazz = (THERE_CAN_BE_ONLY_ONE as
Class)
return clazz.newInstance()
}
}

114. class MacLeod {
THERE_CAN_BE_ONLY_ONE getTHERE_CAN_BE_ONLY_ONE() {
Class<THERE_CAN_BE_ONLY_ONE> clazz = (getTHERE_CAN_BE_ONLY_ONE() as
Class)
return clazz.newInstance()
}
}

118. class Kitty { def fur }
def kitties = [new Kitty(fur: 'soft'),new Kitty(fur: 'warm'),new Kitty(fur: 'purr') ]
println kitties.collect { it.fur }
println kitties*.fur
println kitties.fur

120. class Kitty { def fur }
def kitties
println kitties.collect { it.fur }
println kitties*.fur
println kitties.fur

122. class Kitty { def fur }
def kitties
println kitties.fur

123. class Kitty { def fur }
def kitties
println kitties.fur

124. class Kitty { def fur }
def kitties
println kitties.collect { it.fur }

125. class Kitty { def fur }
def kitties
println kitties.collect { it.fur }
public static Collection asCollection(Object value) {
if (value == null) {
return Collections.EMPTY_LIST;
}
…
}

126. class Kitty { def fur }
def kitties
println kitties*.fur

127. class Kitty { def fur }
def kitties
println kitties*.fur

128. class Kitty { def fur }
def kitties
println kitties*.fur

129. []
null
Caught: java.lang.NullPointerException:
Cannot get property 'fur' on null object

132. ArrayList<String> expendables = ['Arnold', 'Chuck', 'Sylvester']
def expendable = //someone from the list
for(String hero in expendables) {
if(hero == expendable){
expendables.remove(hero)
}
}
println expendables

133. ArrayList<String> expendables = ['Arnold', 'Chuck', 'Sylvester']
def expendable = //someone from the list
for(String hero in expendables) {
if(hero == expendable){
expendables.remove(hero)
}
}
println expendables
A.Can't avoid CME
B.Arnold
C.Chuck
D.Sylvester
Which one won’t cause a
ConcurrentModificationException?

137. List expendables = Arrays.asList(new String[]{"Arnold", "Chuck", "Sylvester"});
String expendable = "Chuck";
Iterator iterator = expendables.iterator();
while(iterator.hasNext()) {
String hero = (String)iterator.next();
if(hero.equals(expendable)) {
expendables.remove(hero);
}
}

138. while(iterator.hasNext()) {
String hero = (String)iterator.next();
if(hero.equals(expendable)) {
// expendables.remove(hero);
}
}

139. while(iterator.hasNext()) {
String hero = (String)iterator.next();
if(hero.equals(expendable)) {
// expendables.remove(hero);
}
}
public E next() {
checkForComodification();
…
cursor = i + 1;
}
Modifications are only
checked in the next
cycle
Getting ready for
hasNext() check in the
next cyclepublic boolean hasNext() {
return cursor != size();
}
Exit on last element +1 ==
size()

140. while(iterator.hasNext()) {
String hero = (String)iterator.next();
if(hero.equals(expendable)) {
// expendables.remove(hero);
}
}
public E next() {
checkForComodification();
…
cursor = i + 1;
}
public boolean hasNext() {
return cursor != size();
}
After Sylvester cursor is 3
And size is 3 as well
All good. Now let’s mess with it.

141. while(iterator.hasNext()) {
String hero = (String)iterator.next();
if(hero.equals(expendable)) {
expendables.remove(hero);
}
}
public E next() {
checkForComodification();
…
cursor = i + 1;
}
public boolean hasNext() {
return cursor != size();
}
After Chuck the cursor is 2
And now the size now is 2!
It won’t get to the next() to run checkForComodification!
Then we remove the element

143. while(iterator.hasNext()) {
String hero = (String)iterator.next();
if(hero.equals(expendable)) {
expendables.remove(hero);
}
}
public E next() {
checkForComodification();
…
cursor = i + 1;
}
public boolean hasNext() {
return cursor != size();
}
After Sylvester the cursor is
3
But the size now is 2!
It will go to another loop and fail on checkForComodification!
Then we remove the element

146. Closure whodunit() {
{
'The butler did it.'
}
}
println whodunit()

148. Closure whodunit() {
{ ->
'The butler did it.'
}
}

151. def range = 1.0..10.0
assert range.contains(5.0)
println range.contains(5.6)

156. Iterator iterator = (1.0..10.0).iterator()
while (iterator.hasNext()) {
print "${iterator.next()} "
}
1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0

162. [0..9].each { println(it - 1) }

172. boolean isPrime(def x) {
if (x == 2) return true
int limit = Math.sqrt(x) + 1
(2..limit).each {
if (x % it == 0) {
return false
}
}
true
}
println isPrime("4" as Double)

174. boolean isPrime(def x) {
if (x == 2) return true
int limit = Math.sqrt(x) + 1
(2..limit).each {
if (x % it == 0) {
return false
}
}
true
}
println isPrime("4" as Double)

175. boolean isPrime(def x) {
if (x == 2) return true
int limit = Math.sqrt(x) + 1
(2..limit).each {
if (x % it == 0) {
return false
}
}
true
}
println isPrime("4" as Double)

182. http://kousenit.wordpress.com/2014/04/

186. A. [[2, 3, 5], [2, 4, 8], [42, 73, 2147483647, 0]]
B. Won't run
C. [[null, null, null, 5]]
D.null

192. def jailhouseRock
def loveMeTender
def rockAroundTheClock = [1,2,3]
jailhouseRock?:[] + loveMeTender?:[] + rockAroundTheClock?:[]
*Yes, we know, it's not Elvis' song.

193. def jailhouseRock
def loveMeTender
def rockAroundTheClock = [1,2,3]
jailhouseRock?:[] + loveMeTender?:[] + rockAroundTheClock?:[]

195. def jailhouseRock
def loveMeTender
def rockAroundTheClock = [1,2,3]
jailhouseRock?:[] + loveMeTender?:[] + rockAroundTheClock?:[]

196. def jailhouseRock
def loveMeTender
def rockAroundTheClock = [1,2,3]
jailhouseRock?:[null]?:[] + rockAroundTheClock?:[]

197. def jailhouseRock
def loveMeTender
def rockAroundTheClock = [1,2,3]
jailhouseRock?:[null]?:[1,2,3]?:[]

198. def jailhouseRock
def loveMeTender
def rockAroundTheClock = [1,2,3]
[null]

199. (jailhouseRock?:[])+(loveMeTender?:[])+(rockAroundTheClock?:[])
Love me tender!

202. double value = 3
println "$value.14".isDouble()

206. double value = 3
println "$value.14".isDouble()

211. List<Long> list = [1,2,3]
def now = new Date()
list << now
println list

212. List<Long> list = [1,2,3]
def now = new Date()
list << now
println list

217. List<Long> list = [1,2,3]
def now = new Date()
list << now
list << 'foo'
println list*.class.name
[java.lang.Long, java.lang.Long,
java.lang.Long, java.util.Date,
java.lang.String]

220. class VanHalen {
public static jump() {
"Here are the ${lyrics()}"
}
def methodMissing(String name, def args) {
'lyrics'
}
}
println VanHalen.jump()

221. class VanHalen {
public static jump()
{
"Here are the
${lyrics()}"
}
def
methodMissing(String
name, def args) {
'lyrics'
}
}

226. class VanHalen {
public static jump() {
"Here are the ${lyrics()}"
}
static $static_methodMissing(String name, def args) {
'lyrics'
}
}
println VanHalen.jump()

227. class VanHalen {
public jump() {
"Here are the ${lyrics()}"
}
def methodMissing(String name, def args) {
'lyrics'
}
}
println new VanHalen().jump()

229. class Invite {
int attending = 1
}
def invite = new Invite()
def attendees = (invite.attending) +1
println attendees

230. class Invite {
int attending = 1
}
def invite = new Invite()
def attendees = (invite.attending) +1
println attendees

236. def attendees = (new Invite().attending) + 1
println attendees
def invite = new Invite()
println (invite.attending +1)

239. def back = 'back'
def quotes = ["I'll be $back",
"I'll be ${-> back}",
"I'll be ${back}",
"I'll be "+back]
println quotes
back = 'Bach'
println quotes

242. def back = 'back'
def quotes = ["I'll be $back",
"I'll be ${-> back}",
"I'll be ${back}",
"I'll be "+back]

243. def back = 'back'
def quotes = ["I'll be $back",
"I'll be ${-> back}",
"I'll be ${back}",
"I'll be "+back]
That is the only closure

246. String truth = 'false'
boolean groovyTruth = truth
println groovyTruth

247. String truth = 'false'
boolean groovyTruth = truth
println groovyTruth

253. assert 1L == 1
println 1L.equals(1)

259. PUBLIC -
PROPERTY!

260. trait Public {
public String property = "I am all public!"
}
class Property implements Public {}
Property publicProperty = new Property()

261. trait Public {
public String property = "I am all public!"
}
class Property implements Public {}
Property publicProperty = new Property()

265. http://beta.groovy-
lang.org/docs/groovy-

267. def map = [metaClass: ‘frequency']
println "What's the $map.metaClass, Frederic?"

270. map.metaClass
map.get('metaClass')
map.getMetaClass()

274. 1. Write readable code
2. Comment neat tricks
3. Sometimes it is just a bug
4. Use static code analysis (intellij IDEA!)
5. Rtfm
6. Don’t code like my brother

275. We have just started!
(may end up in proper uniform)
Puzzlers? Gotchas? Fetal position inducing behavior?
- puzzlers jfrog.com
- Groovypuzzlers

277. Positive feedback?
Praise us on twitter
groovypuzzlers
- Groovypuzzlers
- ryanvanderwerf
- jbaruch
Negative feeback?
/dev/null