/*
* Based on JUEL 2.2.1 code, 2006-2009 Odysseus Software GmbH
*
* 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.activiti.engine.impl.javax.el;
import java.io.Serializable;
import java.util.Hashtable;
/**
* Base class for the expression subclasses {@link ValueExpression} and {@link MethodExpression},
* implementing characterstics common to both. All expressions must implement the equals() and
* hashCode() methods so that two expressions can be compared for equality. They are redefined
* abstract in this class to force their implementation in subclasses. All expressions must also be
* Serializable so that they can be saved and restored. Expressions 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 reparse
* them each time they are evaluated.
*/
public abstract class Expression implements Serializable {
private static final long serialVersionUID = 1L;
/**
* Determines whether the specified object is equal to this Expression. The result is true if
* and only if the argument is not null, is an Expression object that is the of the same type
* (ValueExpression or MethodExpression), and has an identical parsed representation. Note that
* two expressions can be equal if their expression Strings are different. For example,
* ${fn1:foo()} and ${fn2:foo()} are equal if their corresponding FunctionMappers mapped fn1:foo
* and fn2:foo to the same method.
*
* @param obj
* the Object to test for equality.
* @return true if obj equals this Expression; false otherwise.
*/
@Override
public abstract boolean equals(Object obj);
/**
* Returns the original String used to create this Expression, unmodified. This is used for
* debugging purposes but also for the purposes of comparison (e.g. to ensure the expression in
* a configuration file has not changed). This method does not provide sufficient information to
* re-create an expression. Two different expressions can have exactly the same expression
* string but different function mappings. Serialization should be used to save and restore the
* state of an Expression.
*
* @return The original expression String.
*/
public abstract String getExpressionString();
/**
* Returns the hash code for this Expression. See the note in the {@link #equals(Object)} method
* on how two expressions can be equal if their expression Strings are different. Recall that if
* two objects are equal according to the equals(Object) method, then calling the hashCode
* method on each of the two objects must produce the same integer result. Implementations must
* take special note and implement hashCode correctly.
*
* @return The hash code for this Expression.
* @see #equals(Object)
* @see Hashtable
* @see Object#hashCode()
*/
@Override
public abstract int hashCode();
/**
* Returns whether this expression was created from only literal text. This method must return
* true if and only if the expression string this expression was created from contained no
* unescaped EL delimeters (${...} or #{...}).
*
* @return true if this expression was created from only literal text; false otherwise.
*/
public abstract boolean isLiteralText();
}