    001// Copyright 2011 The Apache Software Foundation
    002//
    003// Licensed under the Apache License, Version 2.0 (the "License");
    004// you may not use this file except in compliance with the License.
    005// You may obtain a copy of the License at
    006//
    007// http://www.apache.org/licenses/LICENSE-2.0
    008//
    009// Unless required by applicable law or agreed to in writing, software
    010// distributed under the License is distributed on an "AS IS" BASIS,
    011// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    012// See the License for the specific language governing permissions and
    013// limitations under the License.
    014
    015package org.apache.tapestry5.internal.plastic;
    016
    017import java.util.HashMap;
    018import java.util.Map;
    019
    020/**
    021 * Quick and dirty key/value cache that is subclassed to provide the logic that generates the value for
    022 * a missing key.
    023 *
    024 * @param <S> key type
    025 * @param <T> value type
    026 */
    027public abstract class Cache<S, T>
    028{
    029    private Map<S, T> innerCache = new HashMap<S, T>();
    030
    031    public T get(S input)
    032    {
    033        T result = innerCache.get(input);
    034
    035        if (result == null)
    036        {
    037            result = convert(input);
    038            innerCache.put(input, result);
    039        }
    040
    041        return result;
    042    }
    043
    044    protected abstract T convert(S input);
    045}