To modify the values of a JSONObject in Java, you can use the put method. This method takes the key of the value you want to modify and the new value as arguments. For example:

JSONObject obj = new JSONObject();
obj.put("key", "value");

// To modify the value of "key"
obj.put("key", "new value");

You can also use the get method to retrieve the value of a key, modify it, and then use the put method to update the value in the JSONObject. For example:

String oldValue = obj.getString("key");
String newValue = oldValue + " some additional text";
obj.put("key", newValue);

Keep in mind that the put method can only be used to add or modify key-value pairs in a JSONObject. It cannot be used to add or modify elements in a JSONArray. To do that, you can use the put method of the JSONArray class.