equalsexpression.java

JoSQL 1.5的源代码。JoSQL(SQL for Java Objects)为Java开发者提供运用SQL语句来操作Java对象集的能力.利用JoSQL可以像操作数据库中的数据一样对任何Java

/*
 * Copyright 2004-2005 Gary Bentley 
 * 
 * Licensed under the Apache License, Version 2.0 (the "License"); you may 
 * not use this file except in compliance with the License. 
 * You may obtain a copy of the License at 
 *    http://www.apache.org/licenses/LICENSE-2.0 
 *
 * Unless required by applicable law or agreed to in writing, software 
 * distributed under the License is distributed on an "AS IS" BASIS, 
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 
 * See the License for the specific language governing permissions and 
 * limitations under the License.
 */
package org.josql.expressions;

import org.josql.Query;
import org.josql.QueryExecutionException;

import org.josql.internal.Utilities;

/**
 * This class represents an "=" or "!=" expression.  This class also provides the
 * ability for the developer to prefix the "=" or "!=" with "$" to indicate that a
 * case-insensitive comparison should be made, in which case the LHS and RHS
 * are converted to strings first.
 * <p>
 *  Last Modified By: $Author: barrygently $<br />
 *  Last Modified On: $Date: 2004/12/20 16:22:43 $<br />
 *  Current Revision: $Revision: 1.2 $<br />
 */
public class EqualsExpression extends BinaryExpression
{

    private boolean not = false;

    public boolean ignoreCase = false;

    public void setIgnoreCase (boolean v)
    {

	this.ignoreCase = v;

    }

    public boolean isIgnoreCase ()
    {

	return this.ignoreCase;

    }

    public boolean isNot ()
    {

	return this.not;

    }

    public void setNot (boolean v)
    {

	this.not = v;

    }

    /**
     * Return whether this expression evaluates to <code>true</code>.
     * 
     * @param o The current object to perform the expression on.
     * @param q The Query object.
     * @return <code>true</code> if the expression evaluates to <code>true</code>, <code>false</code>
     *         otherwise.
     * @throws QueryExecutionException If the expression cannot be evaluated.
     */
    public boolean isTrue (Object o,
			   Query  q)
	                   throws QueryExecutionException
    {

	// Get the value for the lhs.
	Object l = null;

	try
	{

	    l = this.left.getValue (o,
				    q);

	} catch (Exception e) {

	    throw new QueryExecutionException ("Unable to get value for LHS of expression: " +
					       this,
					       e);

	}

	Object r = null;

	try
	{

	    r = this.right.getValue (o,
				     q);

	} catch (Exception e) {

	    throw new QueryExecutionException ("Unable to get value for RHS of expression: " +
					       this,
					       e);

	}	

	if ((l == null)
	    &&
	    (r == null)
	   )
	{

	    // Debatable about whether 2 nulls make a true...
	    if (this.not)
	    {

		return false;

	    }

	    return true;

	}

	if ((l == null)
	    ||
	    (r == null)
	   )
	{

	    if (this.not)
	    {

		return true;

	    }

	    // One of them is null, can't do any checking...
	    return false;

	}

	// If we are here then both are NOT NULL.
	return Utilities.matches (l,
				  r,
				  this.ignoreCase,
				  4,
				  this.not);

	/*
	if (this.ignoreCase)
	{

	    // This means that we convert to a String for both and 
	    // compare case-insensitive.
	    String ls = l.toString ();

	    String rs = r.toString ();

	    if ((ls == null)
		||
		(rs == null)
	       )
	    {

		// Can't compare nulls.
		return false;

	    }

	    boolean eq = ls.equalsIgnoreCase (rs);

	    if ((this.not)
		&&
		(!eq)
	       )
	    {

		return true;

	    }

	    if (eq)
	    {

		return true;

	    }

	    return false;

	}

	// See if one of the sides is a number.
	boolean ln = Utilities.isNumber (l);
	boolean rn = Utilities.isNumber (r);

	if (ln
	    &&
	    rn
	   )
	{

	    // They are numbers...
	    double ld = Utilities.getDouble (l);
	    double rd = Utilities.getDouble (r);

	    if (ld == rd)
	    {

		if (this.not)
		{

		    return false;

		}

		return true;

	    }

	    if (this.not)
	    {

		return true;

	    }

	    return false;

	}

	// See if the 2 sides are "comparable".
	// Need to check to see if they are the "same" type... otherwise a CCE will result.
	if ((l instanceof Comparable)
	    &&
	    (r instanceof Comparable)
	    &&
	    (l.getClass ().isAssignableFrom (r.getClass ()))
	   )
	{

	    Comparable lc = (Comparable) l;
	    Comparable rc = (Comparable) r;

	    boolean eq = lc.compareTo (rc) == 0;

	    if ((this.not)
		&&
		(!eq)
	       )
	    {

		return true;

	    }

	    if (eq)
	    {

		return true;

	    }

	    return false;

	}

	// If we are here then one or more of the items does NOT implement Comparable.
	// Force a string comparison.

	String ls = l.toString ();

	String rs = r.toString ();

	if (ls == null)
	{

	    ls = "";

	}

	if (rs == null)
	{

	    rs = "";

	}

	boolean eq = false;

	if (this.ignoreCase)
	{

	    eq = ls.equalsIgnoreCase (rs);

	} else {

	    eq = ls.equals (rs);

	}

	if (eq)
	{

	    if (this.not)
	    {

		return false;

	    }

	    return true;

	} else {

	    if (this.not)
	    {

		return true;

	    }

	    return false;	    

	}
	*/

    }

    /**
     * Return a string version of the expression.
     * In the form: {@link Expression#toString() Expression} [ $ ] [ ! ] = {@link Expression#toString() Expression}
     *
     * @return The string version.
     */
    public String toString ()
    {

	String pred = "=";
	
	if (this.not)
	{

	    pred = "!=";

	}

	if (this.ignoreCase)
	{

	    pred = "$" + pred;

	}

	if (this.isBracketed ())
	{

	    return "(" + this.left.toString () + " " + pred + " " + this.right.toString () + ")";

	}

	return this.left.toString () + " " + pred + " " + this.right.toString ();

    }

}