Is it possible to replace groovy method for existing object?

Question

The following code tried to replace an existing method in a Groovy class:

class A {
  void abc()  {
     println \"original\"
  }
} 

x= new A()
x.abc()
A.me         


        

Answer 1

You can use the per-instance metaClass to change the value in the existing object like so:

x= new A()
x.abc()
x.metaClass.abc={-> println "new" }
x.abc()
x.metaClass.methods.findAll{it.name=="abc"}.each { println "Method $it"}

But as you have seen, x will have two methods associated with it (well, in actual fact, a method and the closure you added

If you change the definition of A so that the method becomes a closure definition like so:

class A {
  def abc = { ->
     println "original"  
  }
} 

Then you will only get a single closure in the metaClass and no method after the alteration