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// **********************************************************************
//
// Copyright (c) 2003-2009 ZeroC, Inc. All rights reserved.
//
// This copy of Ice is licensed to you under the terms described in the
// ICE_LICENSE file included in this distribution.
//
// **********************************************************************
public class Parser
{
public Complex.Node
parse(String buf)
throws ParseError
{
_buf = buf;
_pos = 0;
_token = null;
return start();
}
private Complex.Node
start()
throws ParseError
{
nextToken();
Complex.Node node = expr();
if(_token != null)
{
throw new ParseError("Extra garbage: " + _token);
}
return node;
}
private Complex.Node
expr()
throws ParseError
{
try
{
if(_token == null)
{
return null;
}
//
// '(' expr ')'
//
if(_token.charAt(0) == '(')
{
nextToken();
Complex.Node node = expr();
if(_token.charAt(0) != ')')
{
throw new ParseError("Expected ')'");
}
nextToken();
return node;
}
//
// expr | expr '+' expr | expr '*' expr
//
if(!Character.isDigit(_token.charAt(0)))
{
throw new ParseError("Expected number");
}
Complex.NumberNode number = new Complex.NumberNodeI(Integer.parseInt(_token));
Complex.Node result = number;
//
// expr?
//
nextToken();
if(_token != null)
{
//
// expr '+' expr
//
if(_token.charAt(0) == '+')
{
nextToken();
Complex.Node right = expr();
result = new Complex.AddNodeI(number, right);
}
//
// expr '*' expr
//
else if(_token.charAt(0) == '*')
{
nextToken();
Complex.Node right = expr();
result = new Complex.MultiplyNodeI(number, right);
}
}
return result;
}
catch(NumberFormatException e)
{
ParseError ex = new ParseError("Error parsing number");
ex.initCause(e);
throw ex;
}
}
private void
nextToken()
{
//
// Eat any whitespace.
//
while(_pos < _buf.length() && Character.isWhitespace(_buf.charAt(_pos)))
{
_pos++;
}
//
// At the end-of-buffer?
//
if(_pos >= _buf.length())
{
_token = null;
return;
}
StringBuilder buf = new StringBuilder(128);
//
// Get the next character
//
char c = _buf.charAt(_pos);
//
// '(', ')', '+' and '*' are tokens.
//
if(c == '(' || c == ')' || c == '+' || c == '*')
{
buf.append(c);
++_pos;
}
else
{
//
// Otherwise it's a number.
//
while(_pos < _buf.length() && Character.isDigit(_buf.charAt(_pos)))
{
buf.append(_buf.charAt(_pos++));
}
}
_token = buf.toString();
}
private String _buf;
private int _pos;
private String _token;
}
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