nullliteral.java

来自「RESIN 3.2 最新源码」· Java 代码 · 共 109 行

/*
 * Copyright (c) 1998-2008 Caucho Technology -- all rights reserved
 *
 * This file is part of Resin(R) Open Source
 *
 * Each copy or derived work must preserve the copyright notice and this
 * notice unmodified.
 *
 * Resin Open Source 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 2 of the License, or
 * (at your option) any later version.
 *
 * Resin Open Source 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, or any warranty
 * of NON-INFRINGEMENT.  See the GNU General Public License for more
 * details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Resin Open Source; if not, write to the
 *
 *   Free Software Foundation, Inc.
 *   59 Temple Place, Suite 330
 *   Boston, MA 02111-1307  USA
 *
 * @author Scott Ferguson
 */

package com.caucho.el;

import com.caucho.vfs.WriteStream;

import javax.el.ELContext;
import javax.el.ELException;
import java.io.IOException;

/**
 * Represents a null literal expression.
 */
public class NullLiteral extends Expr {
  /**
   * Create the literal.
   */
  public NullLiteral()
  {
  }

  /**
   * Returns true if the expression is constant.
   */
  @Override
  public boolean isConstant()
  {
    return true;
  }
  
  /**
   * Evaluate the expression as an object.
   *
   * @param env the variable environment
   *
   * @return null
   */
  @Override
  public Object getValue(ELContext env)
    throws ELException
  {
    return null;
  }

  /**
   * Evalutes directly to the output.
   */
  @Override
  public boolean print(WriteStream out, ELContext env, boolean isEscaped)
    throws IOException, ELException
  {
    return false;
  }
  
  /**
   * Prints the code to create an LongLiteral.
   */
  @Override
  public void printCreate(WriteStream os)
    throws IOException
  {
    os.print("new com.caucho.el.NullLiteral()");
  }

  /**
   * Returns true for equal strings.
   */
  public boolean equals(Object o)
  {
    return (o instanceof NullLiteral);
  }

  /**
   * Returns a printable view.
   */
  public String toString()
  {
    return "null";
  }
}