Random item?

[ter0]

So, I was thinking of ways to make a funny and simple mod and I had this idea of a mod that adds new item that can be found somewhere in the Overworld, when you craft this item, you get one random item from vanilla minecraft or any mod you have installed. I know some basic java, but I'm new to modding on minecraft, so my question is, how can you craft an item and as a result you get a completely random item? 

GameRegistry.addRecipe(new ItemStack(woodenSickle), new Object[]{"","a","", 'a', random_item?});

What would I replace "random_item?" with? 

Edited December 16, 2017 by ter0

[Draco18s]

You need to create your own IRecipe implementation.