constantexpression.java

来自「mysql集群」· Java 代码 · 共 60 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;


/**
 * 常量表达式
 * 
 * @author <a href=mailto:[e-mail]>Struct chen</a>
 *
 */
@SuppressWarnings("unchecked")
public class ConstantExpression extends Expression {

	private Comparable value;
	public ConstantExpression(Comparable value) {
		this.value =value;
	}

	@Override
	public Comparable evaluate(Object[] parameters) {
		return value;
	}
	
	public boolean canEvaluate(){
		return true;
	}

	@Override
	public Expression reverse() {
		return this;
	}

	@Override
	protected void toString(StringBuilder builder) {
		Comparable temp = value;
		if(value instanceof String){
			temp = "'"+temp+"'";
			builder.append("'");
			builder.append(value);
			builder.append("'");
		}else{
			builder.append(temp != null?temp.toString():"null");
		}
	}
	
	public boolean isRealtime(){
		return false;
	}
}