https://github.com/google/guice/guice: Guice is a lightweight dependency injection framework for Java 6 and above (Google, Inc.) 
/*
 * Copyright (C) 2008 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.inject.spi;

import com.google.inject.Binder;


A core component of a module or injector.

The elements of a module can be inspected, validated and rewritten. Use Elements.getElements() to read the elements from a module, and Elements.getModule() to rewrite them. This can be used for static analysis and generation of Guice modules. 
The elements of an injector can be inspected and exercised. Use Injector.getBindings() to reflect on Guice injectors. 
Author:jessewilson@google.com (Jesse Wilson), crazybob@google.com (Bob Lee)
Since:2.0
/**
 * A core component of a module or injector.
 *
 * <p>The elements of a module can be inspected, validated and rewritten. Use {@link
 * Elements#getElements(com.google.inject.Module[]) Elements.getElements()} to read the elements
 * from a module, and {@link Elements#getModule(Iterable) Elements.getModule()} to rewrite them.
 * This can be used for static analysis and generation of Guice modules.
 *
 * <p>The elements of an injector can be inspected and exercised. Use {@link
 * com.google.inject.Injector#getBindings Injector.getBindings()} to reflect on Guice injectors.
 *
 * @author jessewilson@google.com (Jesse Wilson)
 * @author crazybob@google.com (Bob Lee)
 * @since 2.0
 */
public interface Element {

  
Returns an arbitrary object containing information about the "place" where this element was
configured. Used by Guice in the production of descriptive error messages.

Tools might specially handle types they know about; StackTraceElement is a good example. Tools should simply call toString() on the source object if the type is unfamiliar. 
/**
   * Returns an arbitrary object containing information about the "place" where this element was
   * configured. Used by Guice in the production of descriptive error messages.
   *
   * <p>Tools might specially handle types they know about; {@code StackTraceElement} is a good
   * example. Tools should simply call {@code toString()} on the source object if the type is
   * unfamiliar.
   */
  Object getSource();

  
Accepts an element visitor. Invokes the visitor method specific to this element's type.

Params:
  • visitor – to call back on
/**
   * Accepts an element visitor. Invokes the visitor method specific to this element's type.
   *
   * @param visitor to call back on
   */
  <T> T acceptVisitor(ElementVisitor<T> visitor);

  
Writes this module element to the given binder (optional operation).

Params:
  • binder – to apply configuration element to
Throws:
/**
   * Writes this module element to the given binder (optional operation).
   *
   * @param binder to apply configuration element to
   * @throws UnsupportedOperationException if the {@code applyTo} method is not supported by this
   *     element.
   */
  void applyTo(Binder binder);
}