How can I solve "org.json.simple.JSONObject cannot be resolved"?

Firstly, you don't need the json-simple.jar in your project.
Therefore remove the import org.json.simple.*

Secondly, the best practice is to import only the required classes from your jar.Therefore you can replace import org.json.*; by

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import org.json.JSONString;

You are missing json-simple-1.1.1.jar from your classpath.

if you are using Maven, add below into your pom.xml.

<dependency>
    <groupId>com.googlecode.json-simple</groupId>
    <artifactId>json-simple</artifactId>
    <version>1.1.1</version>
</dependency>

Or you can download it from here.