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package?lab2.lang;

import?java.util.ArrayList;

import?java.util.HashMap;

import?java.util.List;

import?java.util.Stack;

import?java.util.regex.Matcher;

import?java.util.regex.Pattern;

/**

*?The?ExpressionFactory?class?represents?the?factory?that

*?generates?expressions.

*

*?@author?group7

*

*/

public?class?ExpressionFactory?{

private?HashMap?ops?=?new?HashMap();

private?Pattern?opPattern?=?null;

/**

*?Set?an?operator?in?the?rule.

*

*?@param?op?The?operator.?It?cannot?be?null?or?empty.

*?@param?level?The?priority?of?the?operator.?Bigger?number?represents

*?higher?priority.

*/

public?void?setOp(String?op,?int?level)?{

if?(op?==?null)?{

throw?new?NullPointerException();

}

op?=?op.trim();

if?(op.length()?==?0)?{

throw?new?IllegalArgumentException();

}

ops.put(op,?level);

}

/**

*?Initialize?the?instance.?Must?be?called?before?using?the?instance.

*/

public?void?init()?{

StringBuffer?sb?=?new?StringBuffer();

for?(String?s?:?ops.keySet())?{

sb.append(Pattern.quote(s));

sb.append("|");

}

sb.append("\\(|\\)");

opPattern?=?Pattern.compile(sb.toString());

}

/**

*?Build?an?expression?from?the?string.

*

*?@param?expression?The?expression?string.

*?@return?The?expression.

*?@throws?IllegalArgumentException?If?this?expression?string?is?invalid.

*/

public?Expression?build(String?expression)?{

if?(expression?==?null)?{

throw?new?NullPointerException();

}

expression?=?expression.trim();

if?(expression.length()?==?0)?{

throw?new?IllegalArgumentException("empty?expression");

}

Stack?opStack?=?new?Stack();

List?outputStr?=?new?ArrayList();

List?outputOp?=?new?ArrayList();

int?start?=?0;

Matcher?m?=?opPattern.matcher(expression);

總結

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