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Contains the core Hudson code and view files to render HTML.

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/*******************************************************************************
 *
 * 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 data = new ConcurrentHashMap();

    public  T get(Class type) {
        return type.cast(data.get(type));
    }

    public  T set(Class 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 setIfNull(Class type, T instance) {
        Object o = data.putIfAbsent(type, instance);
        if (o != null) {
            return type.cast(o);
        }
        return instance;
    }
}