IntelliJ IDEA doesn't like a HashMap as delegate - intellij-idea

Question

Let's consider the following code:
class MyClass { //Here:IJ says method putAll not implemented
#Delegate
HashMap<String, Integer> map = new HashMap<String, Integer>()
}
hello = new MyClass()
hello.put("x", 1)
println "x=" + hello.get("x")
It works fine when called with Groovy directly on the command line, but IntelliJ IDEA complains about the first line with the following error message:
Method putAll() is not implemented
Any idea why and how to fix it?

Answer 1

I have experienced the same behavior.
What I found was in my IntelliJ project, the class (MyClass) was showing with the .groovy file extension in the Project view. By doing a refactor-->Rename and removing the .groovy extension, the class would then show without the extension in the Project view and the issue was resolved.
The explanation for the issue came when I tried to run the class, which is really a Groovy Script and not just a plain Class. When it compiles, it would encounter an error:
Invalid duplicate class definition, which gave me a hint that I had created what IntelliJ saw as a Class definition, but was really a Groovy script, so IntelliJ, behind the scenes processed the script and created a second, synthetic class for the script.