Groovy: call operator

The call operator () is used to call a method named call implicitly.

For example,

class Factorial{

         int call(int num){

                  if(num < 0)

                           throw new IllegalArgumentException('input must be >= 0')

                 

                  if(num == 0 || num == 1)

                           return 1

                          

                  int result = 1

                  for(int i = 2; i <= num; i++){

                           result  = result * i

                  }

                 

                  return result

         }

        

}

I can call the call method like below.

Factorial factorial = new Factorial()

int result1 = factorial.call(5)

I can even call the ‘call’ method like below.

int result2 = factorial(5)

HelloWorld.groovy

class Factorial{

 int call(int num){
  if(num < 0)
   throw new IllegalArgumentException('input must be >= 0')
  
  if(num == 0 || num == 1)
   return 1
   
  int result = 1
  for(int i = 2; i <= num; i++){
   result  = result * i
  }
  
  return result
 }
 
}

Factorial factorial = new Factorial()

int result1 = factorial.call(5)
int result2 = factorial(5)

println "Factorial of 5 is ${result1}"
println "Factorial of 5 is ${result2}"

Output

Factorial of 5 is 120

Factorial of 5 is 120

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