166     // maps a module name to a module reference
 167     private final Map<String, ModuleReference> nameToModule;
 168 
 169     // maps a module reference to a module reader
 170     private final Map<ModuleReference, ModuleReader> moduleToReader;
 171 
 172     // cache of resource name -> list of URLs.
 173     // used only for resources that are not in module packages
 174     private volatile SoftReference<Map<String, List<URL>>> resourceCache;
 175 
 176     /**
 177      * Create a new instance.
 178      */
 179     BuiltinClassLoader(String name, BuiltinClassLoader parent, URLClassPath ucp) {
 180         // ensure getParent() returns null when the parent is the boot loader
 181         super(name, parent == null || parent == ClassLoaders.bootLoader() ? null : parent);
 182 
 183         this.parent = parent;
 184         this.ucp = ucp;
 185 
 186         this.nameToModule = new ConcurrentHashMap<>();
 187         this.moduleToReader = new ConcurrentHashMap<>();
 188     }
 189 
 190     /**
 191      * Returns {@code true} if there is a class path associated with this
 192      * class loader.
 193      */
 194     boolean hasClassPath() {
 195         return ucp != null;
 196     }
 197 
 198     /**
 199      * Register a module this class loader. This has the effect of making the
 200      * types in the module visible.
 201      */
 202     public void loadModule(ModuleReference mref) {
 203         String mn = mref.descriptor().name();
 204         if (nameToModule.putIfAbsent(mn, mref) != null) {
 205             throw new InternalError(mn + " already defined to this loader");
 206         }

 166     // maps a module name to a module reference
 167     private final Map<String, ModuleReference> nameToModule;
 168 
 169     // maps a module reference to a module reader
 170     private final Map<ModuleReference, ModuleReader> moduleToReader;
 171 
 172     // cache of resource name -> list of URLs.
 173     // used only for resources that are not in module packages
 174     private volatile SoftReference<Map<String, List<URL>>> resourceCache;
 175 
 176     /**
 177      * Create a new instance.
 178      */
 179     BuiltinClassLoader(String name, BuiltinClassLoader parent, URLClassPath ucp) {
 180         // ensure getParent() returns null when the parent is the boot loader
 181         super(name, parent == null || parent == ClassLoaders.bootLoader() ? null : parent);
 182 
 183         this.parent = parent;
 184         this.ucp = ucp;
 185 
 186         this.nameToModule = new ConcurrentHashMap<>(32);
 187         this.moduleToReader = new ConcurrentHashMap<>();
 188     }
 189 
 190     /**
 191      * Returns {@code true} if there is a class path associated with this
 192      * class loader.
 193      */
 194     boolean hasClassPath() {
 195         return ucp != null;
 196     }
 197 
 198     /**
 199      * Register a module this class loader. This has the effect of making the
 200      * types in the module visible.
 201      */
 202     public void loadModule(ModuleReference mref) {
 203         String mn = mref.descriptor().name();
 204         if (nameToModule.putIfAbsent(mn, mref) != null) {
 205             throw new InternalError(mn + " already defined to this loader");
 206         }