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Java example source code file (Expression.java)

This example Java source code file (Expression.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.

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Java - Java tags/keywords

biginteger, evaluationexception, expression, math, object, string

The Expression.java Java example source code

/*
 * Copyright (c) 1999, 2010, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code 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
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */
/*
 * COMPONENT_NAME: idl.parser
 *
 * ORIGINS: 27
 *
 * Licensed Materials - Property of IBM
 * 5639-D57 (C) COPYRIGHT International Business Machines Corp. 1997, 1999
 * RMI-IIOP v1.0
 *
 */

package com.sun.tools.corba.se.idl.constExpr;

// NOTES:

import java.math.BigInteger;

public abstract class Expression
{
  /**
   * Compute the value of this expression.
   **/
  public abstract Object evaluate () throws EvaluationException;

  /**
   * Set the value of this expression.
   **/
  public void value (Object value)
  {
    _value = value;
  }
  /**
   * Get the value of this expression.
   **/
  public Object value ()
  {
    return _value;
  }

  /**
   * Set the representation of this expression.
   **/
  public void rep (String rep)
  {
    _rep = rep;
  }
  /**
   * Get the representation of this expression.
   **/
  public String rep ()
  {
    return _rep;
  }

  /**
   * Set the target type of this expression.
   **/
  public void type (String type)
  {
    _type = type;
  }
  /**
   * Get the target type of this expression.
   **/
  public String type ()
  {
    return _type;
  }

  /**
   * Return the default computation type for the given target type.
   **/
  protected static String defaultType (String targetType)
  {
    return (targetType == null) ? new String ("") : targetType;
  } // defaultType

  // BigInteger is a multi-precision number whose representation contains
  // a signum (sign-number = 1, -1) and a magnitude.  To support "long long",
  // all integer expressions are now performed over BigInteger and stored as
  // such.  During the evaluation of an integer expression, the signum of its
  // value may toggle, which may cause the value of an expression to conflict
  // with its target type: [Case 1] If the resulting value is negative
  // (signum=-1) and the target type is unsigned; or [Case 2] if the resulting
  // value is positive (signum=1) and greater than 2**(target-type-length - 1),
  // and the target type is signed, then the resulting value will be out of
  // range.  However, this value is correct and must be coerced to the target
  // type.  E.G., After appying "not" to a BigInteger, the result is
  // a BigInteger that represents its 2's-complement (~5 => -6 in a byte-space).
  // In this example, the signum toggles and the magnatude is 6.  If the target
  // type of this value were unsigned short, it must be coerced to a positive
  // number whose bits truly represent -6 in 2's-complement (250 in a byte-space).
  //
  // Also, floating types may now be intialized with any integer expression.
  // The result must be coerced to Double.
  //
  // Use the following routines to coerce this expression's value to its
  // "target" type.

  /**
   * Coerces a number to the target type of this expression.
   * @param  obj  The number to coerce.
   * @return  the value of number coerced to the (target) type of
   *  this expression.
   **/
  public Object coerceToTarget (Object obj)
  {
    if (obj instanceof BigInteger)
    {
      if (type ().indexOf ("unsigned") >= 0)
        return toUnsignedTarget ((BigInteger)obj);
      else
        return toSignedTarget ((BigInteger)obj);
    }
    return obj;
  } // coerceToTarget

  /**
   * Coerces an integral value (BigInteger) to its corresponding unsigned
   * representation, if the target type of this expression is unsigned.
   * @param b The BigInteger to be coerced.
   * @return the value of an integral type coerced to its corresponding
   *  unsigned integral type, if the target type of this expression is
   *  unsigned.
   **/
  protected BigInteger toUnsignedTarget (BigInteger b)
  {
    if (type ().equals ("unsigned short")) // target type of this expression
    {
      if (b != null && b.compareTo (zero) < 0) // error if value < min = -(2**(l-1)).
        return b.add (twoPow16);
    }
    else if (type ().equals ("unsigned long"))
    {
      if (b != null && b.compareTo (zero) < 0)
        return b.add (twoPow32);
    }
    else if (type ().equals ("unsigned long long"))
    {
      if (b != null && b.compareTo (zero) < 0)
        return b.add (twoPow64);
    }
    return b;
  } // toUnsignedTarget

  /**
   * Coerces an integral value (BigInteger) to its corresponding signed
   * representation, if the target type of this expression is signed.
   * @param  b  The BigInteger to be coerced.
   * @return  the value of an integral type coerced to its corresponding
   *  signed integral type, if the target type of this expression is
   *  signed.
   **/
  protected BigInteger toSignedTarget (BigInteger b)
  {
    if (type ().equals ("short"))
    {
      if (b != null && b.compareTo (sMax) > 0)
        return b.subtract (twoPow16);
    }
    else if (type ().equals ("long"))
    {
      if (b != null && b.compareTo (lMax) > 0)
        return b.subtract (twoPow32);
    }
    else if (type ().equals ("long long"))
    {
      if (b != null && b.compareTo (llMax) > 0)
        return b.subtract (twoPow64);
    }
    return b;
  } // toSignedTarget

  /**
   * Return the unsigned value of a BigInteger.
   **/
  protected BigInteger toUnsigned (BigInteger b)
  {
    if (b != null && b.signum () == -1)
      if (type ().equals ("short"))
        return b.add (twoPow16);
      else if (type ().equals ("long"))
        return b.add (twoPow32);
      else if (type ().equals ("long long"))
        return b.add (twoPow64);
    return b;
  }

  // Integral-type boundaries.

  public static final BigInteger negOne = BigInteger.valueOf (-1);
  public static final BigInteger zero   = BigInteger.valueOf (0);
  public static final BigInteger one    = BigInteger.valueOf (1);
  public static final BigInteger two    = BigInteger.valueOf (2);

  public static final BigInteger twoPow15 = two.pow (15);
  public static final BigInteger twoPow16 = two.pow (16);
  public static final BigInteger twoPow31 = two.pow (31);
  public static final BigInteger twoPow32 = two.pow (32);
  public static final BigInteger twoPow63 = two.pow (63);
  public static final BigInteger twoPow64 = two.pow (64);

  public static final BigInteger sMax = BigInteger.valueOf (Short.MAX_VALUE);
  public static final BigInteger sMin = BigInteger.valueOf (Short.MAX_VALUE);

  public static final BigInteger usMax = sMax.multiply (two).add (one);
  public static final BigInteger usMin = zero;

  public static final BigInteger lMax = BigInteger.valueOf (Integer.MAX_VALUE);
  public static final BigInteger lMin = BigInteger.valueOf (Integer.MAX_VALUE);

  public static final BigInteger ulMax = lMax.multiply (two).add (one);
  public static final BigInteger ulMin = zero;

  public static final BigInteger llMax = BigInteger.valueOf (Long.MAX_VALUE);
  public static final BigInteger llMin = BigInteger.valueOf (Long.MIN_VALUE);

  public static final BigInteger ullMax = llMax.multiply (two).add (one);
  public static final BigInteger ullMin = zero;

  /**
   * Value of this expression: Boolean, Char, Byte, BigInteger, Double,
   * String, Expression, ConstEntry.
   **/
  private Object _value = null;
  /**
   * String representation of this expression.
   **/
  private String _rep   = null;
  /**
   * Computation type of this (sub)expression = Target type for now.
   **/
  private String _type  = null;
} // abstract class Expression

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