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/*
* Copyright (c) 1997, 2019 Oracle and/or its affiliates and others.
* All rights reserved.
* 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 jakarta.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 Jakarta Server Pages 2.1
*/
public abstract class Expression implements Serializable {
private static final long serialVersionUID = -6663767980471823812L;
/**
* 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)
*/
@Override
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()
*/
@Override
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 Jakarta Expression Language delimeters (<code>${...}</code> or <code>#{...}</code>).
*
* @return <code>true</code> if this expression was created from only literal text; <code>false</code> otherwise.
*/
public abstract boolean isLiteralText();
}
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