content: /*
   * Copyright 1999-2012 Alibaba Group.
   *  
   * 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.
   */
  /**
   * (created at 2011-7-25)
   */
  package com.alibaba.cobar.parser.ast.expression;
  
  import java.util.Map;
  
  /**
   * @author <a href="mailto:shuo.qius@alibaba-inc.com">QIU Shuo</a>
   */
  public abstract class AbstractExpression implements Expression {
      private boolean cacheEvalRst = true;
      private boolean evaluated;
      private Object evaluationCache;
  
      @Override
      public Expression setCacheEvalRst(boolean cacheEvalRst) {
          this.cacheEvalRst = cacheEvalRst;
          return this;
      }
  
      @Override
      public final Object evaluation(Map<? extends Object, ? extends Object> parameters) {
          if (cacheEvalRst) {
              if (evaluated) {
                  return evaluationCache;
              }
              evaluationCache = evaluationInternal(parameters);
              evaluated = true;
              return evaluationCache;
          }
          return evaluationInternal(parameters);
      }
  
      protected abstract Object evaluationInternal(Map<? extends Object, ? extends Object> parameters);
  
  }
  