default boolean hasClass(final String className) throws IOException {
    return getClassBytes(className) != null;
  }
Returns whether a class exists in this source.

@param className the class name, with no trailing {@code /}
@return true if the class exists, false otherwise
@throws IOException if an error is encountered while checking if the class exists
src/org/jetbrains/java/decompiler/main/extern/IContextSource.java