java - Passing json array in a key value pair

Question

I want to know how to pass the json array as key in a json object.

{   
  "name" :"Sam", 
  "grades": [{"maths": "A", "result":"pass"}, {"science": "B", "result":"pass"}]
}

I couldn't pass both the values to 'grades' in jSONObject. I Looped it. But, it simply overwrites the values.