Java example source code file (Code.java)

This example Java source code file (Code.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

adjust, attribute, code, codeexception, constantpool, datainputstream, from\\tto\\thandler\\ttype\\n, ioexception, length, linenumbertable, localvariabletable, maximum, overwrites, stringbuffer

The Code.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.*;

/**
 * This class represents a chunk of Java byte code contained in a
 * method. It is instantiated by the
 * <em>Attribute.readAttribute() method. A Code
 * attribute contains informations about operand stack, local
 * variables, byte code and the exceptions handled within this
 * method.
 *
 * This attribute has attributes itself, namely <em>LineNumberTable which
 * is used for debugging purposes and <em>LocalVariableTable which
 * contains information about the local variables.
 *
 * @author  <A HREF="mailto:markus.dahm@berlin.de">M. Dahm
 * @see     Attribute
 * @see     CodeException
 * @see     LineNumberTable
 * @see LocalVariableTable
 */
public final class Code extends Attribute {
  private int             max_stack;   // Maximum size of stack used by this method
  private int             max_locals;  // Number of local variables
  private int             code_length; // Length of code in bytes
  private byte[]          code;        // Actual byte code

  private int             exception_table_length;
  private CodeException[] exception_table;  // Table of handled exceptions
  private int             attributes_count; // Attributes of code: LineNumber
  private Attribute[]     attributes;       // or LocalVariable

  /**
   * Initialize from another object. Note that both objects use the same
   * references (shallow copy). Use copy() for a physical copy.
   */
  public Code(Code c) {
    this(c.getNameIndex(), c.getLength(), c.getMaxStack(), c.getMaxLocals(),
         c.getCode(), c.getExceptionTable(), c.getAttributes(),
         c.getConstantPool());
  }

  /**
   * @param name_index Index pointing to the name <em>Code
   * @param length Content length in bytes
   * @param file Input stream
   * @param constant_pool Array of constants
   */
  Code(int name_index, int length, DataInputStream file,
       ConstantPool constant_pool) throws IOException
  {
    // Initialize with some default values which will be overwritten later
    this(name_index, length,
         file.readUnsignedShort(), file.readUnsignedShort(),
         (byte[])null, (CodeException[])null, (Attribute[])null,
         constant_pool);

    code_length = file.readInt();
    code = new byte[code_length]; // Read byte code
    file.readFully(code);

    /* Read exception table that contains all regions where an exception
     * handler is active, i.e., a try { ... } catch() block.
     */
    exception_table_length = file.readUnsignedShort();
    exception_table        = new CodeException[exception_table_length];

    for(int i=0; i < exception_table_length; i++)
      exception_table[i] = new CodeException(file);

    /* Read all attributes, currently `LineNumberTable' and
     * `LocalVariableTable'
     */
    attributes_count = file.readUnsignedShort();
    attributes = new Attribute[attributes_count];
    for(int i=0; i < attributes_count; i++)
      attributes[i] = Attribute.readAttribute(file, constant_pool);

    /* Adjust length, because of setAttributes in this(), s.b.  length
     * is incorrect, because it didn't take the internal attributes
     * into account yet! Very subtle bug, fixed in 3.1.1.
     */
    this.length = length;
  }

  /**
   * @param name_index Index pointing to the name <em>Code
   * @param length Content length in bytes
   * @param max_stack Maximum size of stack
   * @param max_locals Number of local variables
   * @param code Actual byte code
   * @param exception_table Table of handled exceptions
   * @param attributes Attributes of code: LineNumber or LocalVariable
   * @param constant_pool Array of constants
   */
  public Code(int name_index, int length,
              int max_stack,  int max_locals,
              byte[]          code,
              CodeException[] exception_table,
              Attribute[]     attributes,
              ConstantPool    constant_pool)
  {
    super(Constants.ATTR_CODE, name_index, length, constant_pool);

    this.max_stack         = max_stack;
    this.max_locals        = max_locals;

    setCode(code);
    setExceptionTable(exception_table);
    setAttributes(attributes); // Overwrites length!
  }

  /**
   * 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 void accept(Visitor v) {
    v.visitCode(this);
  }

  /**
   * Dump code attribute to file stream in binary format.
   *
   * @param file Output file stream
   * @throws IOException
   */
  public final void dump(DataOutputStream file) throws IOException
  {
    super.dump(file);

    file.writeShort(max_stack);
    file.writeShort(max_locals);
    file.writeInt(code_length);
    file.write(code, 0, code_length);

    file.writeShort(exception_table_length);
    for(int i=0; i < exception_table_length; i++)
      exception_table[i].dump(file);

    file.writeShort(attributes_count);
    for(int i=0; i < attributes_count; i++)
      attributes[i].dump(file);
  }

  /**
   * @return Collection of code attributes.
   * @see Attribute
   */
  public final Attribute[] getAttributes()         { return attributes; }

  /**
   * @return LineNumberTable of Code, if it has one
   */
  public LineNumberTable getLineNumberTable() {
    for(int i=0; i < attributes_count; i++)
      if(attributes[i] instanceof LineNumberTable)
        return (LineNumberTable)attributes[i];

    return null;
  }

  /**
   * @return LocalVariableTable of Code, if it has one
   */
  public LocalVariableTable getLocalVariableTable() {
    for(int i=0; i < attributes_count; i++)
      if(attributes[i] instanceof LocalVariableTable)
        return (LocalVariableTable)attributes[i];

    return null;
  }

  /**
   * @return Actual byte code of the method.
   */
  public final byte[] getCode()      { return code; }

  /**
   * @return Table of handled exceptions.
   * @see CodeException
   */
  public final CodeException[] getExceptionTable() { return exception_table; }

  /**
   * @return Number of local variables.
   */
  public final int  getMaxLocals() { return max_locals; }

  /**
   * @return Maximum size of stack used by this method.
   */

  public final int  getMaxStack()  { return max_stack; }

  /**
   * @return the internal length of this code attribute (minus the first 6 bytes)
   * and excluding all its attributes
   */
  private final int getInternalLength() {
    return 2 /*max_stack*/ + 2 /*max_locals*/ + 4 /*code length*/
      + code_length /*byte-code*/
      + 2 /*exception-table length*/
      + 8 * exception_table_length /* exception table */
      + 2 /* attributes count */;
  }

  /**
   * @return the full size of this code attribute, minus its first 6 bytes,
   * including the size of all its contained attributes
   */
  private final int calculateLength() {
    int len = 0;

    for(int i=0; i < attributes_count; i++)
      len += attributes[i].length + 6 /*attribute header size*/;

    return len + getInternalLength();
  }

  /**
   * @param attributes.
   */
  public final void setAttributes(Attribute[] attributes) {
    this.attributes  = attributes;
    attributes_count = (attributes == null)? 0 : attributes.length;
    length = calculateLength(); // Adjust length
  }

  /**
   * @param code byte code
   */
  public final void setCode(byte[] code) {
    this.code   = code;
    code_length = (code == null)? 0 : code.length;
  }

  /**
   * @param exception_table exception table
   */
  public final void setExceptionTable(CodeException[] exception_table) {
    this.exception_table   = exception_table;
    exception_table_length = (exception_table == null)? 0 :
      exception_table.length;
  }

  /**
   * @param max_locals maximum number of local variables
   */
  public final void setMaxLocals(int max_locals) {
    this.max_locals = max_locals;
  }

  /**
   * @param max_stack maximum stack size
   */
  public final void setMaxStack(int max_stack) {
    this.max_stack = max_stack;
  }

  /**
   * @return String representation of code chunk.
   */
  public final String toString(boolean verbose) {
    StringBuffer buf;

    buf = new StringBuffer("Code(max_stack = " + max_stack +
                           ", max_locals = " + max_locals +
                           ", code_length = " + code_length + ")\n" +
                           Utility.codeToString(code, constant_pool, 0, -1, verbose));

    if(exception_table_length > 0) {
      buf.append("\nException handler(s) = \n" + "From\tTo\tHandler\tType\n");

      for(int i=0; i < exception_table_length; i++)
        buf.append(exception_table[i].toString(constant_pool, verbose) + "\n");
    }

    if(attributes_count > 0) {
      buf.append("\nAttribute(s) = \n");

      for(int i=0; i < attributes_count; i++)
        buf.append(attributes[i].toString() + "\n");
    }

    return buf.toString();
  }

  /**
   * @return String representation of code chunk.
   */
  public final String toString() {
    return toString(true);
  }

  /**
   * @return deep copy of this attribute
   */
  public Attribute copy(ConstantPool constant_pool) {
    Code c = (Code)clone();
    c.code          = (byte[])code.clone();
    c.constant_pool = constant_pool;

    c.exception_table = new CodeException[exception_table_length];
    for(int i=0; i < exception_table_length; i++)
      c.exception_table[i] = exception_table[i].copy();

    c.attributes = new Attribute[attributes_count];
    for(int i=0; i < attributes_count; i++)
      c.attributes[i] = attributes[i].copy(constant_pool);

    return c;
  }
}