Lectura y Reconocimiento de Números Complejos

Sigue un ejemplo:

~/Lgroovy/overloading$ cat -n  ComplexNumber.groovy 
 1  class MyComplex  {
 2    def real, imaginary
 3  
 4    def plus(other) {
 5      new MyComplex(
 6            real: real+other.real,
 7            imaginary: imaginary+other.imaginary
 8      )
 9    }
10  
11    String toString() {
12      "$real "+(imaginary > 0? "+${imaginary}i" : '')
13    }
14  
15    def static _numre = /\s*([-+]?\d+(?:\.\d*)?)\s*/
16    def static _complexre = ~/^\s*${_numre}\s*(?:\+\s*${_numre}i)?$/
17  
18    def static read() {
19  
20      def scanner = new Scanner(System.in)
21  
22      print "Enter a complex number (e.g. 2+1i): ";
23      def input = scanner.nextLine()
24  
25      def m = (input =~ _complexre);
26      if (m) {
27        m = m[0]
28        def re = m[1].toDouble()
29        def im = m[2]? m[2].toDouble() : 0.0;
30  
31        return new MyComplex(real : re, imaginary: im)
32      }
33  
34      throw new Exception("\n\tExpected a complex number. Found: '$input'\n")
35    }
36  
37  }
38  
39  c1 = MyComplex.read()
40  c2 = MyComplex.read()
41  
42  println c1+c2

Ejecución:

~/Lgroovy/overloading$ groovy ComplexNumber.groovy 
Enter a complex number (e.g. 2+1i): 2+3i
Enter a complex number (e.g. 2+1i): 4+5i
6.0 +8.0i
~/Lgroovy/overloading$ groovy ComplexNumber.groovy 
Enter a complex number (e.g. 2+1i): juf+plos i
Caught: java.lang.Exception: 
        Expected a complex number. Found: 'juf+plos i'

        at MyComplex.read(ComplexNumber.groovy:34)
        at ComplexNumber.run(ComplexNumber.groovy:39)
~/Lgroovy/overloading$ groovy ComplexNumber.groovy 
Enter a complex number (e.g. 2+1i): 2
Enter a complex number (e.g. 2+1i): 3
5.0 
~/Lgroovy/overloading$ groovy ComplexNumber.groovy 
Enter a complex number (e.g. 2+1i): 2+i
Caught: java.lang.Exception: 
        Expected a complex number. Found: '2+i'

        at MyComplex.read(ComplexNumber.groovy:34)
        at ComplexNumber.run(ComplexNumber.groovy:39)