/*******************************************************************************
*
* Copyright (c) 2010, Oracle Corporation
*
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/legal/epl-v10.html
*
* Contributors:
*
*
* Kohsuke Kawaguchi
*
*******************************************************************************/
package hudson;
import java.util.concurrent.ConcurrentHashMap;
/**
* Type-safe instance map.
*
* @author Kohsuke Kawaguchi
*/
public class Lookup {
private final ConcurrentHashMap<Class, Object> data = new ConcurrentHashMap<Class, Object>();
public <T> T get(Class<T> type) {
return type.cast(data.get(type));
}
public <T> T set(Class<T> type, T instance) {
return type.cast(data.put(type, instance));
}
/**
* Overwrites the value only if the current value is null.
*
* @return If the value was null, return the {@code instance} value.
* Otherwise return the current value, which is non-null.
*/
public <T> T setIfNull(Class<T> type, T instance) {
Object o = data.putIfAbsent(type, instance);
if (o != null) {
return type.cast(o);
}
return instance;
}
}