ifcommand.java

java设计模式源码

package com.oozinoz.robotInterpreter2;

/*
 * Copyright (c) 2001, 2005. Steven J. Metsker.
 * 
 * Steve Metsker makes no representations or warranties about
 * the fitness of this software for any particular purpose, 
 * including the implied warranty of merchantability.
 *
 * Please use this software as you wish with the sole
 * restriction that you may not claim that you wrote it.
 */

/**
*  This class represents an "if" statement that will execute
*  one of two commands depending on the value of a supplied
*  conditional term.
*/
public class IfCommand extends Command {
    protected Term term;
    protected Command body;
    protected Command elseBody;

    /**
    *  Construct an "if" command that will execute its "else" body
    *  if the supplied term is null, and will otherwise execute
    *  its regular body.
    *  @param term the term to evaluate to determine which body to
    *  execute
    *  @param body the body to execute if the term is true
    *  @param elseBody the body to execute if the term is false
    */
    public IfCommand(Term term, Command body, Command elseBody) {
        this.term = term;
        this.body = body;
        this.elseBody = elseBody;
    }

    /**
    *  Execute this object's "else" body if this object's term
    *  evaluates to null; otherwise execute the main body.
    */
    public void execute() {
        if (term.eval() != null)
            body.execute();
        else
            elseBody.execute();
    }
}