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/*
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
*
* Copyright (c) 1997-2013 Oracle and/or its affiliates. All rights reserved.
*
* The contents of this file are subject to the terms of either the GNU
* General Public License Version 2 only ("GPL") or the Common Development
* and Distribution License("CDDL") (collectively, the "License"). You
* may not use this file except in compliance with the License. You can
* obtain a copy of the License at
* https://glassfish.dev.java.net/public/CDDL+GPL_1_1.html
* or packager/legal/LICENSE.txt. See the License for the specific
* language governing permissions and limitations under the License.
*
* When distributing the software, include this License Header Notice in each
* file and include the License file at packager/legal/LICENSE.txt.
*
* GPL Classpath Exception:
* Oracle designates this particular file as subject to the "Classpath"
* exception as provided by Oracle in the GPL Version 2 section of the License
* file that accompanied this code.
*
* Modifications:
* If applicable, add the following below the License Header, with the fields
* enclosed by brackets [] replaced by your own identifying information:
* "Portions Copyright [year] [name of copyright owner]"
*
* Contributor(s):
* If you wish your version of this file to be governed by only the CDDL or
* only the GPL Version 2, indicate your decision by adding "[Contributor]
* elects to include this software in this distribution under the [CDDL or GPL
* Version 2] license." If you don't indicate a single choice of license, a
* recipient has the option to distribute your version of this file under
* either the CDDL, the GPL Version 2 or to extend the choice of license to
* its licensees as provided above. However, if you add GPL Version 2 code
* and therefore, elected the GPL Version 2 license, then the option applies
* only if the new code is made subject to such option by the copyright
* holder.
*
*
* This file incorporates work covered by the following copyright and
* permission notice:
*
* Copyright 2004 The Apache Software Foundation
*
* 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 javax.el;
import java.io.Serializable;
/**
* Base class for the expression subclasses {@link ValueExpression} and
* {@link MethodExpression}, implementing characteristics common to both.
*
* <p>All expressions must implement the <code>equals()</code> and
* <code>hashCode()</code> methods so that two expressions can be compared
* for equality. They are redefined abstract in this class to force their
* implementation in subclasses.</p>
*
* <p>All expressions must also be <code>Serializable</code> so that they
* can be saved and restored.</p>
*
* <p><code>Expression</code>s are also designed to be immutable so
* that only one instance needs to be created for any given expression
* String / {@link FunctionMapper}. This allows a container to pre-create
* expressions and not have to re-parse them each time they are evaluated.</p>
*
* @since JSP 2.1
*/
public abstract class Expression
implements Serializable {
// Debugging
/**
* Returns the original String used to create this <code>Expression</code>,
* unmodified.
*
* <p>This is used for debugging purposes but also for the purposes
* of comparison (e.g. to ensure the expression in a configuration
* file has not changed).</p>
*
* <p>This method does not provide sufficient information to
* re-create an expression. Two different expressions can have exactly
* the same expression string but different function mappings.
* Serialization should be used to save and restore the state of an
* <code>Expression</code>.</p>
*
* @return The original expression String.
*/
public abstract String getExpressionString();
// Comparison
/**
* Determines whether the specified object is equal to this
* <code>Expression</code>.
*
* <p>The result is <code>true</code> if and only if the argument is
* not <code>null</code>, is an <code>Expression</code> object that
* is the of the same type (<code>ValueExpression</code> or
* <code>MethodExpression</code>), and has an identical parsed
* representation.</p>
*
* <p>Note that two expressions can be equal if their expression
* Strings are different. For example, <code>${fn1:foo()}</code>
* and <code>${fn2:foo()}</code> are equal if their corresponding
* <code>FunctionMapper</code>s mapped <code>fn1:foo</code> and
* <code>fn2:foo</code> to the same method.</p>
*
* @param obj the <code>Object</code> to test for equality.
* @return <code>true</code> if <code>obj</code> equals this
* <code>Expression</code>; <code>false</code> otherwise.
* @see java.util.Hashtable
* @see java.lang.Object#equals(java.lang.Object)
*/
public abstract boolean equals(Object obj);
/**
* Returns the hash code for this <code>Expression</code>.
*
* <p>See the note in the {@link #equals} method on how two expressions
* can be equal if their expression Strings are different. Recall that
* if two objects are equal according to the <code>equals(Object)</code>
* method, then calling the <code>hashCode</code> method on each of the
* two objects must produce the same integer result. Implementations must
* take special note and implement <code>hashCode</code> correctly.</p>
*
* @return The hash code for this <code>Expression</code>.
* @see #equals
* @see java.util.Hashtable
* @see java.lang.Object#hashCode()
*/
public abstract int hashCode();
/**
* Returns whether this expression was created from only literal text.
*
* <p>This method must return <code>true</code> if and only if the
* expression string this expression was created from contained no
* unescaped EL delimeters (<code>${...}</code> or
* <code>#{...}</code>).</p>
*
* @return <code>true</code> if this expression was created from only
* literal text; <code>false</code> otherwise.
*/
public abstract boolean isLiteralText();
}