java - ClassCastException on custom class loading -

i'm trying write scripting system in java , i've managed scripts compile , instantiate when try cast script "deftscript" throws classcasterror thought script extends class "deftscript"

error (the important part @ least):

java.lang.classcastexception: scripts.compass cannot cast com.deft.core.scripts.deftscript     @ com.deft.core.scripts.deftscriptmanager.instantiate(deftscriptmanager.java:52) ~[?:?] 

the error caused this

deftscript = (deftscript)obj; 

compiling , instantiating:

public static deftscript instantiate(string java) {     file file = new file("./plugins/deft-core/scripts/" + java);      deftscript deftscript = null;      diagnosticcollector<javafileobject> diagnostics = new diagnosticcollector<javafileobject>();     javacompiler compiler = toolprovider.getsystemjavacompiler();     standardjavafilemanager filemanager = compiler.getstandardfilemanager(diagnostics, null, null);      list<string> optionlist = new arraylist<string>();     optionlist.addall(arrays.aslist("-classpath", system.getproperty("java.class.path") + ";./plugins/deft-core.jar"));       iterable<? extends javafileobject> compilationunit = filemanager.getjavafileobjectsfromfiles(arrays.aslist(file));     javacompiler.compilationtask task = compiler.gettask(null, filemanager, diagnostics, optionlist, null, compilationunit);     if (task.call()) {          object obj = null;         try {             string jarfile = "./plugins/deft-core.jar";             urlclassloader classloader = new urlclassloader (new url[] {new file(jarfile).touri().tourl(), new file("./plugins/deft-core/").touri().tourl()}, thread.currentthread().getcontextclassloader());              class<?> loadedclass;             loadedclass = class.forname("scripts.compass", false, classloader);             obj = loadedclass.newinstance();          } catch (classnotfoundexception | instantiationexception | illegalaccessexception | malformedurlexception e) {             e.printstacktrace();         }           deftscript = (deftscript)obj;         deftscript.onenable();     } else {         (diagnostic<? extends javafileobject> diagnostic : diagnostics.getdiagnostics()) {             system.out.format("error on line %d in %s%n", diagnostic.getlinenumber(), diagnostic.getsource().touri());         }     }      return deftscript; } 

calling instantiate method:

string script = "compass.java"; deftscriptmanager.instantiate(script); 

deftscript.java

package com.deft.core.scripts;  public abstract class deftscript {     public abstract void onenable(); } 

compass.java

package scripts; import com.deft.core.scripts.deftscript; public class compass extends deftscript {     @override     public void onenable() {} } 

if default classloader loads class deftscript , .jar loading contains class deftscript, java think these 2 different classes same binary name loaded different classloaders , exception since java sees trying mix 2 different classes same thing.

the unique identification of class in java consists of binary class name , classloader used load class.

if create urlclassloader :

urlclassloader classloader =      new urlclassloader (new url[] {new file(jarfile).touri().tourl(),      new file("./plugins/deft-core/").touri().tourl()},            thread.currentthread().getcontextclassloader()); 

the second parameter tells java use current thread's classloader first load classes, , load them jar in urlclassloader if not defined in parent.

now classloader refer it's parent first , class deftscript loaded parent classloader though .jar file defines same class (by name).

this pretty article describing way works :

http://www2.sys-con.com/itsg/virtualcd/java/archives/0808/chaudhri/index.html

this helpful

http://www.javaworld.com/article/2077344/core-java/find-a-way-out-of-the-classloader-maze.html?page=1