If you pass a negative number to the Math.sqrt method, it will return a value called NaN Not A Number.

examples/groovy/sqrt.groovy

println( Math.sqrt( 4 ))    // 2.0
println( Math.sqrt( -1 ))   // NaN
println('still alive')      // still alive

What if you'd like to write your own sqrt function that will throw an exception if a negative value is passed to it?

Here is a solution:

examples/groovy/my_sqrt.groovy

def sqrt(int n) {
    if (n < 0) {
        throw new Exception("The number ${n} was negative")
    }
    return Math.sqrt(n)
}


println( sqrt( 4 ))    // 2.0
println( sqrt( -1 ))   // exception
println('still alive') // is not executed...

2.0
Caught: java.lang.Exception: The number -1 was negative
java.lang.Exception: The number -1 was negative
	at my_sqrt.sqrt(my_sqrt.groovy:4)
	at my_sqrt$sqrt.callCurrent(Unknown Source)
	at my_sqrt.run(my_sqrt.groovy:11)

The code that would print "still alive" is not executed.

Catch my exception

examples/groovy/catch_my_sqrt.groovy

def sqrt(int n) {
    if (n < 0) {
        throw new Exception("The number ${n} was negative")
    }
    return Math.sqrt(n)
}


println( sqrt( 4 ))    // 2.0
try {
   println( sqrt( -1 ))
} catch(Exception e) {
    println("Exception: ${e}")
}                      // Exception: java.lang.Exception: The number -1 was negative
println('still alive') // still alive