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30 day Evaluation Version distributed via the Maven Jar Repository. Clover is not free. You have 30 days to evaluate it. Please visit http://www.thecortex.net/clover to obtain a licensed version of Clover | |||||||||||||||||||
Source file | Conditionals | Statements | Methods | TOTAL | |||||||||||||||
Parser.java | 100% | 100% | 100% | 100% |
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// Copyright 2004, 2005 The Apache Software Foundation
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package org.apache.hivemind.conditional;
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import org.apache.hivemind.util.Defense;
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/**
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* Parser for conditional expressions. This class is not threadsafe; it is inexpensive to create,
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* however, and can be discarded after parsing one or more expressions.
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*
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* @author Howard M. Lewis Ship
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* @since 1.1
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*/
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public class Parser |
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{ |
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private String _input;
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private Lexer _lexer;
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private Token _nextToken;
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private boolean _onDeck; |
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// No reason to have multiple instances of these, since they are always
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// identical (one of the advantages of the NodeImpl being purely structural.
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private static final Evaluator NOT_EVALUATOR = new NotEvaluator(); |
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private static final Evaluator OR_EVALUATOR = new OrEvaluator(); |
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private static final Evaluator AND_EVALUATOR = new AndEvaluator(); |
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public Node parse(String input)
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{ |
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Defense.notNull(input, "input");
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try
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{ |
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_input = input; |
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_lexer = new Lexer(input);
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Node result = expression(); |
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Token token = next(); |
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if (token != null) |
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throw new RuntimeException(ConditionalMessages.unparsedToken(token, _input)); |
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return result;
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} |
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finally
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{ |
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_input = null;
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_nextToken = null;
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_lexer = null;
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_onDeck = false;
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} |
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} |
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private Token next()
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{ |
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Token result = _onDeck ? _nextToken : _lexer.next(); |
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_onDeck = false;
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_nextToken = null;
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return result;
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} |
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private Token match(TokenType expected)
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{ |
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Token actual = next(); |
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if (actual == null) |
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throw new RuntimeException(ConditionalMessages.unexpectedEndOfInput(_input)); |
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if (actual.getType() != expected)
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throw new RuntimeException(ConditionalMessages.unexpectedToken(expected, actual |
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.getType(), _input)); |
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return actual;
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} |
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private Token peek()
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{ |
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if (! _onDeck)
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{ |
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_nextToken = _lexer.next(); |
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_onDeck = true;
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} |
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return _nextToken;
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} |
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private TokenType peekType()
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{ |
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Token next = peek(); |
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return next == null ? null : next.getType(); |
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} |
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private boolean isPeek(TokenType type) |
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{ |
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return peekType() == type;
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} |
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private Node expression()
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{ |
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Node lnode = term(); |
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if (isPeek(TokenType.OR))
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{ |
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next(); |
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Node rnode = expression(); |
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return new NodeImpl(lnode, rnode, OR_EVALUATOR); |
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} |
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if (isPeek(TokenType.AND))
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{ |
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next(); |
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Node rnode = expression(); |
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return new NodeImpl(lnode, rnode, AND_EVALUATOR); |
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} |
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return lnode;
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} |
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private Node term()
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{ |
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if (isPeek(TokenType.OPAREN))
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{ |
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next(); |
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Node result = expression(); |
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match(TokenType.CPAREN); |
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return result;
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} |
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if (isPeek(TokenType.NOT))
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{ |
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next(); |
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match(TokenType.OPAREN); |
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Node expression = expression(); |
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match(TokenType.CPAREN); |
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return new NodeImpl(expression, null, NOT_EVALUATOR); |
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} |
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if (isPeek(TokenType.PROPERTY))
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{ |
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next(); |
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Token symbolToken = match(TokenType.SYMBOL); |
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Evaluator ev = new PropertyEvaluator(symbolToken.getValue());
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return new NodeImpl(ev); |
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} |
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if (isPeek(TokenType.CLASS))
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{ |
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next(); |
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Token symbolToken = match(TokenType.SYMBOL); |
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Evaluator ev = new ClassNameEvaluator(symbolToken.getValue());
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return new NodeImpl(ev); |
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} |
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throw new RuntimeException(ConditionalMessages.unparsedToken(next(), _input)); |
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} |
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} |
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