org.apache.felix.dependencymanager/src/main/java/org/apache/felix/dependencymanager/DefaultNullObject.java

/*
 *   Copyright 2006 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 org.apache.felix.dependencymanager;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;


/**
 * Default null object implementation. Uses a dynamic proxy. Null objects are used
 * as placeholders for services that are not available.
 * 
 * @author <a href="mailto:felix-dev@incubator.apache.org">Felix Project Team</a>
 */
public class DefaultNullObject implements InvocationHandler {
    private static final Boolean DEFAULT_BOOLEAN = Boolean.FALSE;
    private static final Byte DEFAULT_BYTE = new Byte((byte) 0);
    private static final Short DEFAULT_SHORT = new Short((short) 0);
    private static final Integer DEFAULT_INT = new Integer(0);
    private static final Long DEFAULT_LONG = new Long(0);
    private static final Float DEFAULT_FLOAT = new Float(0.0f);
    private static final Double DEFAULT_DOUBLE = new Double(0.0);
    
    /**
     * Invokes a method on this null object. The method will return a default
     * value without doing anything.
     */
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        Class returnType = method.getReturnType();
        if (returnType.equals(Boolean.class) || returnType.equals(Boolean.TYPE)) {
            return DEFAULT_BOOLEAN;
        }
        else if (returnType.equals(Byte.class) || returnType.equals(Byte.TYPE)) {
            return DEFAULT_BYTE;
        } 
        else if (returnType.equals(Short.class) || returnType.equals(Short.TYPE)) {
            return DEFAULT_SHORT;
        } 
        else if (returnType.equals(Integer.class) || returnType.equals(Integer.TYPE)) {
            return DEFAULT_INT;
        } 
        else if (returnType.equals(Long.class) || returnType.equals(Long.TYPE)) {
            return DEFAULT_LONG;
        } 
        else if (returnType.equals(Float.class) || returnType.equals(Float.TYPE)) {
            return DEFAULT_FLOAT;
        } 
        else if (returnType.equals(Double.class) || returnType.equals(Double.TYPE)) {
            return DEFAULT_DOUBLE;
        } 
        else {
            return null;
        }
    }
}