same linkedlist code different behavior between groovy and java, why

Question

I am using linkedlist as a stack in groovy

as doc says, pop() take elm from the first

Stack Method  Equivalent Deque Method  
push(e)       addFirst(e) 
pop()         removeFirst()

so a linkedlist [1,2,3] should pop() 1 2 3

and it does in Java, but does NOT in groovy. WHY?

test below

A.java

import java.util.*;

public class A{


    public static void main(String[] args){

        String[] x = "1/2/3/".split("/");
        LinkedList <String> stack = new LinkedList<String>(Arrays.asList(x));
        System.out.println(stack.pop());
    }
}

compile and run

$ javac A.java
$ java A
1

runing in groovy

$ ln -s A.java A.groovy
$ groovy A.groovy
3

here is my java and groovy version

$ java -version
java version "1.6.0_51"
Java(TM) SE Runtime Environment (build 1.6.0_51-b11-457-11M4509)
Java HotSpot(TM) 64-Bit Server VM (build 20.51-b01-457, mixed mode)

$ groovy -version
Groovy Version: 2.1.5 JVM: 1.6.0_51 Vendor: Apple Inc. OS: Mac OS X

Answer 1

This appears to be a "feature" of groovy. Default Groovy Methods are described as This class defines new groovy methods which appear on normal JDK classes inside the Groovy environment.

One of the methods that DefaultGroovyMethods provides is pop(), which is described as: Removes the last item from the List. So it appears that Groovy is weaving in a different implementation of pop() which is conflicting with what LinkedList provides you by default.

A bug report filed against GDM a few years ago describes it best, and provides some additional commentary: LinkedList seems to implement List and a pop/push method, thus the classes method should not be shadowed by a DGM method. Only if we had a LinkedList#pop/push method in DGM, it should be different.