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org.activiti.engine.impl.javax.el.Expression Maven / Gradle / Ivy
/*
* 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 characteristics 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
* ${fn2:foo()} are equal if their corresponding FunctionMappers mapped fn1:foo and fn2:foo to the same method.
*
* @param obj
* the Object to test for equality.
* @return true if obj equals this Expression; false otherwise.
*/
@Override
public abstract boolean equals(Object obj);
/**
* Returns the original String used to create this Expression, unmodified. This is used for debugging purposes but also for the purposes of comparison (e.g. to ensure the expression in a
* configuration file has not changed). This method does not provide sufficient information to re-create an expression. Two different expressions can have exactly the same expression string but
* different function mappings. Serialization should be used to save and restore the state of an Expression.
*
* @return The original expression String.
*/
public abstract String getExpressionString();
/**
* Returns the hash code for this Expression. See the note in the {@link #equals(Object)} method on how two expressions can be equal if their expression Strings are different. Recall that if two
* objects are equal according to the equals(Object) method, then calling the hashCode method on each of the two objects must produce the same integer result. Implementations must take special note
* and implement hashCode correctly.
*
* @return The hash code for this Expression.
* @see #equals(Object)
* @see Hashtable
* @see Object#hashCode()
*/
@Override
public abstract int hashCode();
/**
* Returns whether this expression was created from only literal text. This method must return true if and only if the expression string this expression was created from contained no unescaped EL
* delimiters (${...} or #{...}).
*
* @return true if this expression was created from only literal text; false otherwise.
*/
public abstract boolean isLiteralText();
}