expression.java

来自「mysql集群」· Java 代码 · 共 55 行

/*
 * 	This program is free software; you can redistribute it and/or modify it under the terms of 
 * the GNU General Public License as published by the Free Software Foundation; either version 3 of the License, 
 * or (at your option) any later version. 
 * 
 * 	This program is distributed in the hope that it will be useful, 
 * but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  
 * See the GNU General Public License for more details. 
 * 	You should have received a copy of the GNU General Public License along with this program; 
 * if not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 */
package com.meidusa.amoeba.parser.expression;


/**
 * 表达式基类
 * 
 * @author <a href=mailto:[e-mail]>Struct chen</a>
 *
 */
public abstract class Expression {
	
	public Expression(){
	}
	public boolean canEvaluate(){
		return true;
	}
	
	/**
	 * 表达式取反
	 * @return
	 */
	public abstract Expression reverse();
	
	protected abstract void toString(StringBuilder builder);
	
	/**
	 * 表示该表达式是否需要实时计算
	 * @return
	 */
	public abstract boolean isRealtime();
	/**
	 * 表达式计算
	 * @return
	 */
	@SuppressWarnings("unchecked")
	public abstract Comparable evaluate(Object[] parameters);

	public String toString(){
		StringBuilder builder = new StringBuilder();
		this.toString(builder);
		return builder.toString();
	}
}