Wednesday, May 06, 2009

0.0 Is A BigDecimal In Groovy!

When you are so used to the convenience offered by Groovy and Grails, sometimes you are caught by simplicity itself.

I created a domain class recently:

class Foo {
double price

static constraints = {
price(min: 0.0)

Boom! The application failed to run with the error message:

Parameter for constraint [min] of property [value] of class [class Foo]
must be the same type as property: [double]

The cause of the problem is that I declared price to be a double, but 0.0 is a BigDecimal in Groovy. To fix the problem, change the value to 0.0d. I found the answer from this thread.

When Class.forName() Can't Find The Domain Class

I was trying to use reflection to create a domain class:

try {
def clazz = Class.forName(domainClassName)
def obj = clazz.newInstance()
catch (ClassNotFoundException ex) {

To my surprise, I caught ClassNotFoundException at line 2. After searching for a while, I found an explanation in this thread. Burt Beckwith explained that classes loaded without a ClassLoader will not resolve dynamically added classes such as the domain classes. He suggested to use the other variant:

try {
def clazz = Class.forName(domainClassName, true, Thread.currentThread().contextClassLoader)
obj = clazz.newInstance()
catch (ClassNotFoundException ex) {

Thanks for the tips, Burt.

Saturday, May 02, 2009

Self-printing Groovy Program

It always amazes me when I read about how people write a C program that print itself. The self-printing program, or more formally, quine, prints out its source code.

Having used Groovy for a while, I wonder if there is any self-printing Groovy program on the Internet. After some googling around, I found some Java programs on this page. After spending about 15 minutes, I came up with what I think is the first self-printing Groovy program to date. I used Bertram Felgenhauer's 2nd example as my starting point. Here is my version in Groovy (the code is written in one line):

class S{public static void main(a){def s="class S{public static void main(a){def s=;char c=34;println(s.substring(0,41)+c+s+c+s.substring(41));}}";char c=34;println(s.substring(0,41)+c+s+c+s.substring(41));}}

See if you can make it shorter.


Chrigel suggested the removal of "public". I have to adjust the parameter to substring() too. Here is a shorter version (195 bytes):

class S{static void main(a){def s="class S{static void main(a){def s=;char c=34;println(s.substring(0,34)+c+s+c+s.substring(34));}}";char c=34;println(s.substring(0,34)+c+s+c+s.substring(34));}}

paulk's version is 97 bytes:

def s="def s=;char c=34;println s[0..5]+c+s+c+s[6..-1]";char c=34;println s[0..5]+c+s+c+s[6..-1]

paulk's 2nd version is 46 bytes:

s="s=%c%s%c;printf s,34,s,34";printf s,34,s,34

paulk's 3rd version is 42 bytes. Keep going, paulk!

s='s=%c%s%1$c;printf s,39,s';printf s,39,s

Gavin Grover found a 38-char solution at

printf _='printf _=%c%s%1$c,39,_',39,_

Are we approaching the limit?