Iterating through nested Json Array and performing operations on String Java

I have json array in this format

    [
{
    "promise_detail": [
        {
            "promise_date": "15 OCT 2020",
            "promise_amount": "USD 1086",
            "status": "CANCELLED"
        }
    ],
    "promise_note": "hello"
}

]

My requirement is i need to loop through Json array and format promise amount field to two decimal places which looks like "USD 1086.00"

Here is what i am trying to do

    result = executeQueries.getPromiseHistoryDetails(promiseHistoryModel);//Here result is same Json Array as shown above
    for (int n = 0; n < result.length(); n++) {
			JSONObject object = result.getJSONObject(n);
			for(int k=0;k<object.length();k++) {  //struck here
				String promiseAmount = object.getJSONObject(k);
                Float amount=Float.parseFloat(promiseAmount);
				if (object.get("promise_amount") != null) {
					DecimalFormat df = new DecimalFormat("0.00");
					df.setMaximumFractionDigits(2);
					result.getJSONObject(n).put("promise_amount", df.format(amount));
				}
			}
			
		}

But I am getting some issues.I am struck at this point.Can anyone suggest me how i can achieve this.This is my expected output

    [
{
    "promise_detail": [
        {
            "promise_date": "15 OCT 2020",
            "promise_amount": "USD 1086.00",
            "status": "CANCELLED"
        }
    ],
    "promise_note": "hello"
}
]

It seems you mixed up the operation of JSONArray with JSONObject. The inner for-loop is supposed to traverse a JSONArray rather than a JSONObject.

And the format of promise_amount in your given JSON string is a String, so you can just append .00 to the origin value as follows:

Code snippet

for (int n = 0; n < result.length(); n++) {
    JSONArray object = result.getJSONObject(n).getJSONArray("promise_detail");
    for (int k = 0; k < object.length(); k++) {
        String promiseAmount = object.getJSONObject(k).getString("promise_amount");
        if (promiseAmount != null) {
            object.getJSONObject(k).put("promise_amount", String.format("%s.00", promiseAmount));
        }
    }
}