code: public static void registerHandler( Class valueType, Class<? extends OptionHandler> handlerClass ) {
          checkNonNull(valueType, "valueType");
          checkNonNull(handlerClass, "handlerClass");
  
          OptionHandlerRegistry.getRegistry().registerHandler(valueType, handlerClass);
      }
docs: Registers a user-defined {@link OptionHandler} class with args4j.
  
  <p>
  This method allows users to extend the behavior of args4j by writing
  their own {@link OptionHandler} implementation.
  
  @param valueType
  The specified handler is used when the field/method annotated by {@link Option}
  is of this type.
  @param handlerClass
  This class must have the constructor that has the same signature as
  {@link OptionHandler#OptionHandler(CmdLineParser, OptionDef, Setter)}
  @throws NullPointerException if {@code valueType} or {@code handlerClass} is {@code null}.
  @throws IllegalArgumentException if {@code handlerClass} is not a subtype of {@code OptionHandler}.
  @deprecated You should use {@link OptionHandlerRegistry#registerHandler(java.lang.Class, java.lang.Class)} instead.