Why I can use method 'each' in List interface in Groovy?

Question

I am a beginner for Groovy. I feel confused for the List interface. According the type, it is an instance of java.util.ArrayList . And there is no method each in Java JDK for ArrayList.

Why I can type below code:

list = [1, 2, 3]
list.each { println "- ${it}" }

println list.class

Answer 1

Groovy adds methods to existing classes to support its coding style.

For example these are all the methods added to the List interface, including the each method .

A rough overview over the additional features added this way can be found in the Groovy Development Kit overview page .