apache/hadoop · error · RuntimeException

{} not {}

Error message

{} not {}

What it means

Error "{} not {}" thrown in apache/hadoop.

Source

Thrown at hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/conf/Configuration.java:2751

   * returned.
   * 
   * An exception is thrown if the returned class does not implement the named
   * interface. 
   * 
   * @param name the conf key name.
   * @param defaultValue default value.
   * @param xface the interface implemented by the named class.
   * @param <U> Interface class type.
   * @return property value as a <code>Class</code>, 
   *         or <code>defaultValue</code>.
   */
  public <U> Class<? extends U> getClass(String name, 
                                         Class<? extends U> defaultValue, 
                                         Class<U> xface) {
    try {
      Class<?> theClass = getClass(name, defaultValue);
      if (theClass != null && !xface.isAssignableFrom(theClass))
        throw new RuntimeException(theClass+" not "+xface.getName());
      else if (theClass != null)
        return theClass.asSubclass(xface);
      else
        return null;
    } catch (Exception e) {
      throw new RuntimeException(e);
    }
  }

  /**
   * Get the value of the <code>name</code> property as a <code>List</code>
   * of objects implementing the interface specified by <code>xface</code>.
   * 
   * An exception is thrown if any of the classes does not exist, or if it does
   * not implement the named interface.
   * 
   * @param name the property name.
   * @param xface the interface implemented by the classes named by

View on GitHub (pinned to 2add963021)

Solutions

1. The configured class is not of the expected type; configure a class of the required interface.

Example fix

Use a class implementing the expected interface.

When it happens

Trigger: Raised at runtime when the documented precondition or configuration requirement for this operation is violated.

Common situations: Misconfigured or missing property, invalid user input, or calling the API before its prerequisites are met.

AI-assisted analysis of apache/hadoop@2add963021 (2026-08-22). Data as JSON: /api/errors/d8c860c27af0cab4. Report an issue: GitHub.