Java example source code file (Constant.java)

This example Java source code file (Constant.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

classformatexception, clonenotsupportedexception, constant, constantclass, constantfieldref, constantfloat, constantinteger, constantinterfacemethodref, constantstring, invalid, ioexception, node, object, serializable

The Constant.java Java example source code

/*
 * reserved comment block
 * DO NOT REMOVE OR ALTER!
 */
package com.sun.org.apache.bcel.internal.classfile;

/* ====================================================================
 * The Apache Software License, Version 1.1
 *
 * Copyright (c) 2001 The Apache Software Foundation.  All rights
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution,
 *    if any, must include the following acknowledgment:
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowledgment may appear in the software itself,
 *    if and wherever such third-party acknowledgments normally appear.
 *
 * 4. The names "Apache" and "Apache Software Foundation" and
 *    "Apache BCEL" must not be used to endorse or promote products
 *    derived from this software without prior written permission. For
 *    written permission, please contact apache@apache.org.
 *
 * 5. Products derived from this software may not be called "Apache",
 *    "Apache BCEL", nor may "Apache" appear in their name, without
 *    prior written permission of the Apache Software Foundation.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 */

import  com.sun.org.apache.bcel.internal.Constants;
import  java.io.*;

/**
 * Abstract superclass for classes to represent the different constant types
 * in the constant pool of a class file. The classes keep closely to
 * the JVM specification.
 *
 * @author  <A HREF="mailto:markus.dahm@berlin.de">M. Dahm
 */
public abstract class Constant implements Cloneable, Node, Serializable {
  /* In fact this tag is redundant since we can distinguish different
   * `Constant' objects by their type, i.e., via `instanceof'. In some
   * places we will use the tag for switch()es anyway.
   *
   * First, we want match the specification as closely as possible. Second we
   * need the tag as an index to select the corresponding class name from the
   * `CONSTANT_NAMES' array.
   */
  protected byte tag;

  Constant(byte tag) { this.tag = tag; }

  /**
   * Called by objects that are traversing the nodes of the tree implicitely
   * defined by the contents of a Java class. I.e., the hierarchy of methods,
   * fields, attributes, etc. spawns a tree of objects.
   *
   * @param v Visitor object
   */
  public abstract void accept(Visitor v);

  public abstract void dump(DataOutputStream file) throws IOException;

  /**
   * @return Tag of constant, i.e., its type. No setTag() method to avoid
   * confusion.
   */
  public final byte getTag() { return tag; }

  /**
   * @return String representation.
   */
  public String toString() {
    return Constants.CONSTANT_NAMES[tag] + "[" + tag + "]";
  }

  /**
   * @return deep copy of this constant
   */
  public Constant copy() {
    try {
      return (Constant)super.clone();
    } catch(CloneNotSupportedException e) {}

    return null;
  }

  public Object clone() throws CloneNotSupportedException {
    return super.clone();
  }

  /**
   * Read one constant from the given file, the type depends on a tag byte.
   *
   * @param file Input stream
   * @return Constant object
   */
  static final Constant readConstant(DataInputStream file)
    throws IOException, ClassFormatException
  {
    byte b = file.readByte(); // Read tag byte

    switch(b) {
    case Constants.CONSTANT_Class:              return new ConstantClass(file);
    case Constants.CONSTANT_Fieldref:           return new ConstantFieldref(file);
    case Constants.CONSTANT_Methodref:          return new ConstantMethodref(file);
    case Constants.CONSTANT_InterfaceMethodref: return new
                                        ConstantInterfaceMethodref(file);
    case Constants.CONSTANT_String:             return new ConstantString(file);
    case Constants.CONSTANT_Integer:            return new ConstantInteger(file);
    case Constants.CONSTANT_Float:              return new ConstantFloat(file);
    case Constants.CONSTANT_Long:               return new ConstantLong(file);
    case Constants.CONSTANT_Double:             return new ConstantDouble(file);
    case Constants.CONSTANT_NameAndType:        return new ConstantNameAndType(file);
    case Constants.CONSTANT_Utf8:               return new ConstantUtf8(file);
    default:
      throw new ClassFormatException("Invalid byte tag in constant pool: " + b);
    }
  }
}