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/*
*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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.apache.qpid.qmf2.common;
// Misc Imports
import java.util.Iterator;
import java.util.List;
/**
* This class represents the base class for all Expressions created by expanding the Query predicate.
* <p>
* Depending on the structure of the expression list there might be a nested structure of Expressions comprising
* a mixture of LogicalExpressions and BooleanExpressions.
* <p>
* The Expression structure is illustrated below in the context of its relationship with QmfQuery.
* <img alt="" src="doc-files/QmfQuery.png">
*
* @author Fraser Adams
*/
public abstract class Expression
{
/**
* Factory method to create concrete Expression instances base on the operator name extracted from the expression List.
* This method will create a LogicalExpression from an "and", "or" or "not" operator otherwise it will create
* a BooleanExpression.
*
* @param expr the List of Expressions extracted by parsing the Query predicate
*/
public static Expression createExpression(final List expr) throws QmfException
{
Iterator iter = expr.listIterator();
if (!iter.hasNext())
{
throw new QmfException("Missing operator in predicate expression");
}
String op = (String)iter.next();
if (op.equals("not"))
{
return new LogicalNot(expr);
}
if (op.equals("and"))
{
return new LogicalAnd(expr);
}
if (op.equals("or"))
{
return new LogicalOr(expr);
}
return BooleanExpression.createExpression(expr);
}
/**
* Evaluate expression against a QmfData instance.
* @return true if query matches the QmfData instance, else false.
*/
public abstract boolean evaluate(final QmfData data);
}
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