Unlike the "strongly typed" languges, Groovy does not check the existance of all the variables at compile time. This can lead to run-time exceptions such as groovy.lang.MissingPropertyException

examples/groovy/undeclared_variable.groovy

print "Input: "
def val = System.in.newReader().readLine() as Integer

if (val > 10) {
   println "bigger than 10"
} else if (value < 10) {
   println "smaller than 10"
} else {
   println "it is 10"
}

In this script we declare and use a variable called val, but in one point, in the second if-statement, we used the variable name value. Presumably by mistake.

If the input is 10 or more the code runs smoothly, but if the input is less than 10 then we get a run-time exception: 

Caught: groovy.lang.MissingPropertyException: No such property: value for class: undeclared_variable
groovy.lang.MissingPropertyException: No such property: value for class: undeclared_variable
	at undeclared_variable.run(undeclared_variable.groovy:6)