changes getDefinedPackage back to getPackage when Java is < 9.

build.xml

   <path id="test.compile.classpath">
     <pathelement location="${build.classes.dir}"/>
     <pathelement location="${lib.dir}/junit.jar"/>
+    <pathelement location="${lib.dir}/hamcrest.jar"/>
   </path>
 
   <property name="test.compile.classpath" refid="test.compile.classpath"/>
   <path id="test.classpath">
     <pathelement location="${test.build.dir}"/>
     <pathelement location="${lib.dir}/junit.jar"/>
-  	<pathelement location="${build.classes.dir}"/>
+    <pathelement location="${lib.dir}/hamcrest.jar"/>
+    <pathelement location="${build.classes.dir}"/>
   </path>
 
   <property name="test.classpath" refid="test.classpath"/>

src/main/javassist/Loader.java

 import java.util.Hashtable;
 import java.util.Vector;
 
+import javassist.bytecode.ClassFile;
+
 /**
  * The class loader for Javassist.
  *
         int i = name.lastIndexOf('.');
         if (i != -1) {
             String pname = name.substring(0, i);
-            if (getDefinedPackage(pname) == null)
+            if (isDefinedPackage(pname))
                 try {
                     definePackage(
                         pname, null, null, null, null, null, null, null);
         return defineClass(name, classfile, 0, classfile.length, domain);
     }
 
+    private boolean isDefinedPackage(String name) {
+        if (ClassFile.MAJOR_VERSION >= ClassFile.JAVA_9)
+            return getDefinedPackage(name) == null;
+        else
+            return getPackage(name) == null;
+    }
+
     protected Class<?> loadClassByDelegation(String name)
         throws ClassNotFoundException
     {