Is it possible to create object without declaring class?

In Groovy you must always provide the class of an object being created, so there is no equivalent in Groovy to JavaScript's object-literal syntax.

However, Groovy does have a literal syntax for a Map, which is conceptually very similar to a JavaScript object, i.e. both are a collection of properties or name-value pairs.

The equivalent Groovy code to the JavaScript above is:

def obj = [a: '1']
println obj.a

Even though there is no class name used here you're still creating an object of a particular class (java.util.LinkedHashMap). The code above is just shorthand for:

def obj = new LinkedHashMap();
obj.a = '1'
println obj.a

The Expando class is perhaps even more similar to a JavaScript object, and is useful when you want to avoid the "overhead" of defining a class, or want a dynamic object to which any arbitrary property can be added at runtime.

Groovy has an equivalent notation for json. Only difference is they use [:] for maps instead of {}. So you can clearly convert a json into a groovy object notation.

import groovy.json.JsonOutput

def obj = [:] //define map
obj.batsmen = [] //define array 
def b = [:] 
b.name= "V. Kohli"
b.score = 55
b.strike = false

obj.batsmen.push(b)

//push second object
obj.batsmen.push(b)
println JsonOutput.toJson(obj)

Here I have not printed the object directly. Since it will print with square braces notation.

Read the whole article. Groovy for javascript developers. https://metamug.com/article/groovy-for-javascript-developers.php

Slightly surprised that nobody has mentioned the Expando class. This adds extra functionality over a map in that you can directly reference properties within your functions. Code example below.

def expando = new Expando(a:"def")
expando.run = {def b ->
println("$a")
println("$b")
}
expando.run("ABC")

def map = [a:"def"]
map.run = {def b ->
 println("$a") //THIS DOES NOT WORK.  You will get a missing property exception.
 println("$b")
}
map.run("ABC")

printed output:

def

ABC

groovy.lang.MissingPropertyException

ABC (if you comment out the println($a) in the map.run, println($b) prints out ABC)

Ignore the extra line breaks in the output. Was having a heck of a time putting def and ABC on consecutive lines.

See the Expando API documentation for more information.