apache/hadoop · error · RuntimeException

{} does not implement {}

Error message

{} does not implement {}

What it means

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

Source

Thrown at hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/conf/Configuration.java:2780

   * 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
   *        <code>name</code>.
   * @param <U> Interface class type.
   * @return a <code>List</code> of objects implementing <code>xface</code>.
   */
  @SuppressWarnings("unchecked")
  public <U> List<U> getInstances(String name, Class<U> xface) {
    List<U> ret = new ArrayList<U>();
    Class<?>[] classes = getClasses(name);
    for (Class<?> cl: classes) {
      if (!xface.isAssignableFrom(cl)) {
        throw new RuntimeException(cl + " does not implement " + xface);
      }
      ret.add((U)ReflectionUtils.newInstance(cl, this));
    }
    return ret;
  }

  /** 
   * Set the value of the <code>name</code> property to the name of a 
   * <code>theClass</code> implementing the given interface <code>xface</code>.
   * 
   * An exception is thrown if <code>theClass</code> does not implement the 
   * interface <code>xface</code>. 
   * 
   * @param name property name.
   * @param theClass property value.
   * @param xface the interface implemented by the named class.
   */
  public void setClass(String name, Class<?> theClass, Class<?> xface) {

View on GitHub (pinned to 2add963021)

Solutions

1. Configure a class that implements the required interface named in the message.

Example fix

Implement the interface in the configured class.

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/cc2533d82fb386c7. Report an issue: GitHub.