Custom Class Loader For Loading JAR Files

I'm writing a custom class loader to load some .jar file

public class IQJarClassLoader extends ClassLoader { 
private String jarFile = "json-simple-1.1.1.jar";
private Hashtable classes = new Hashtable();
public IQJarClassLoader() {
super(IQJarClassLoader.class.getClassLoader());

[Code] .....

I receive this exception :

Exception in thread "main" java.lang.ClassCastException: org.json.simple.parser.JSONParser cannot be cast to org.json.simple.parser.JSONParser

Everytime, because i don't cast. Casting an object to a class with the same name loaded by different classloaders is no different than trying to cast.