Json Object Array Length

Javascript is case sensitive. Change this.Groups.length to this.groups.length.

This code should work:

$.each(myJsonObject.Apps, function() { 
   alert(this.groups.length);
}); 

I have a working example on JSFiddle

To avoid this sort of problem, you should use a consistent capitalization. In Javascript, it is conventional to use camelCase.

this works well:

HTML:

<span id="result"></span>

JS:

var myJsonObject = 
{ 
   "Apps" : [
   { 
     "Name" : "app1",
     "id" : "1",
     "groups" : [ 
       { "id" : "1", "name" : "test group 1", "desc" : "this is a test group" },
       { "id" : "2", "name" : "test group 2", "desc" : "this is another test group" } 
     ]
   }
   ]
};

$.each(myJsonObject.Apps, function(i, el) { 
    $("#result").html(el.groups.length);
});

example

Looks like you just have a simple typo in your code. JavaScript is case-sensitive, so groups is not the same as Groups.

If your JSON object has groups in all lowercase, like your example, then you only need to use this.groups.length inside the iteration function.

Try this: function objectCount(obj) {

objectcount = 0;
$.each(obj, function(index, item) {
    objectcount = objectcount + item.length;
});
return objectcount;
}
objectCount(obj);

where obj is a json object with json array as sub objects

Try this

import org.json.JSONObject;

JSONObject myJsonObject = new JSONObject(yourJson);
int length = myJsonObject.getJSONArray("groups").length();