Here is some code using java 6 to get you started:

JSONObject jo = new JSONObject();
jo.put("firstName", "John");
jo.put("lastName", "Doe");

JSONArray ja = new JSONArray();
ja.put(jo);

JSONObject mainObj = new JSONObject();
mainObj.put("employees", ja);

Edit: Since there has been a lot of confusion about put vs add here I will attempt to explain the difference. In java 6 org.json.JSONArray contains the put method and in java 7 javax.json contains the add method.

An example of this using the builder pattern in java 7 looks something like this:

JsonObject jo = Json.createObjectBuilder()
  .add("employees", Json.createArrayBuilder()
    .add(Json.createObjectBuilder()
      .add("firstName", "John")
      .add("lastName", "Doe")))
  .build();

The exception occurred because your input JSON string is not properly assigned to JSONObject. There is no constructor like JSONObject(StringBuffer). Just Change it to JSONObject(String) or JSONObject(StringBufferObject.toString())

also, add ]} at the end of your input JSON string.

public static void parseJson(StringBuffer sb) throws JSONException {

    JSONObject obj = new JSONObject(sb.toString());


    JSONArray arr = obj.getJSONArray("value");

    for (int i = 0; i < arr.length(); i++) {
        System.out.println(arr.getJSONObject(i).getString("Name"));
    }
}