Java8のOptional

optional.groovy

def opt = Optional.of("HOGE")
assert opt.get() == "HOGE"
assert opt.isPresent()
assert opt.map { it * 2 }.get() == "HOGEHOGE"
assert opt.flatMap { Optional.of(it * 2) }.get() == 'HOGEHOGE'

assert opt.map { null } == Optional.empty()

// Optional.of(null) // => NPE

def nullOpt = Optional.ofNullable(null)
assert nullOpt == Optional.empty()
assert nullOpt.isPresent() == false
assert nullOpt.orElse("FOO") == "FOO"
assert nullOpt.map { it * 2 } == Optional.empty()
assert nullOpt.flatMap { Optional.of(it * 2) } == Optional.empty()