http://groups.google.com/group/jggug/browse_thread/thread/a35e9abf90790391

g100ponNo55.groovy

// g100pon No.55 multi method dispatching

def typeOf(Object o)  { 'This is Object'  }
def typeOf(String s)  { 'This is String'  }
def typeOf(Integer i) { 'This is Integer' }
def typeOf(List l)    { 'This is List'    }
def typeOf(Map m)     { 'This is Map'     }

Object o = new Object()
assert typeOf(o) == 'This is Object'
assert o.class.name == 'java.lang.Object'

Object s = "hogehoge"
assert typeOf(s) == 'This is String'       // => Javaでは'This is Object'になる
assert s.class.name == 'java.lang.String'  // => JavaでもこれはString

Object i = 123
assert typeOf(i) == 'This is Integer'      // => Javaでは'This is Object'になる
assert i.class.name == 'java.lang.Integer' // => JavaでもこれはInteger

Object l = ['a', 'b', 'c', 1, 2, 3]
assert typeOf(l) == 'This is List'           // => Javaでは'This is Object'になる
assert l.class.name == 'java.util.ArrayList' // => JavaでもこれはArrayList

Object m = ['a':1, 'b':2, 'c':3]
assert typeOf(m) == 'This is Map'                     // => Javaでは'This is Object'になる
assert m.getClass().name == 'java.util.LinkedHashMap' // => JavaでもこれはLinkedHashMap