Question

I’d like to re-implement a method of a Java class. For example, for "hi".length() to return 4. (How) Can I do that?

I know using SomeClass.metaClass I can get a reference to an existing method and define new (or overriding) method, but I can’t seem to be able to do that for existing Java methods.

Answer 1

Seems like it could be possible by abusing String metaClass. But the attempt I’ve done so far in groovy console didn’t led to the expected result :

def oldLength = String.metaClass.length
String.metaClass.length = { ->
    return oldLength+10;
}

println "hi".length()

outputs the sad 2

I think you could take a look at Proxy MetaClass or Delegating metaClass.