https://github.com/cglib/cglib/cglib: cglib is a powerful, high performance and quality Code Generation Library, It is used to extend JAVA classes and implements interfaces at runtime. 
/*
 * Copyright 2003 The Apache Software Foundation
 *
 *  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 net.sf.cglib.proxy;


Enhancer callback that simply returns the value to return from the proxied method. No information about what method is being called is available to the callback, and the type of the returned object must be compatible with the return type of the proxied method. This makes this callback primarily useful for forcing a particular method (through the use of a CallbackFilter to return a fixed value with little overhead. 
/**
 * {@link Enhancer} callback that simply returns the value to return
 * from the proxied method. No information about what method
 * is being called is available to the callback, and the type of
 * the returned object must be compatible with the return type of
 * the proxied method. This makes this callback primarily useful
 * for forcing a particular method (through the use of a {@link CallbackFilter}
 * to return a fixed value with little overhead.
 */
public interface FixedValue extends Callback {
    
Return the object which the original method invocation should
return. This method is called for every method invocation.

Returns:an object matching the type of the return value for every
method this callback is mapped to
/**
     * Return the object which the original method invocation should
     * return. This method is called for <b>every</b> method invocation.
     * @return an object matching the type of the return value for every
     * method this callback is mapped to
     */
    Object loadObject() throws Exception;
}