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  1. import java.util.regex.Matcher;
  2. import java.util.regex.Pattern;
  3.  
  4. public class Lexer {
  5.  
  6. 	public static class Token
  7. 	{
  8. 		public int tokenNumber;
  9. 		public String tokenValue;
  10.  
  11. 		public Token(int tokenNumber, String tokenValue)
  12. 		{
  13. 			this.tokenNumber = tokenNumber;
  14. 			this.tokenValue = tokenValue;
  15. 		}
  16. 	}
  17.  
  18.     public static int WHITESPACE = 1; // group 1
  19.     public static int PUNCTUATION = 2; // group 2 etc.
  20.     public static int LPAREN = 3;
  21.     public static int RPAREN = 4;
  22.     public static int KEYWORD = 5;
  23.     public static int IDENTIFIER = 6;
  24.     public static int NUMBER = 7;
  25.     public static int SEMICOLON = 8;
  26.     public static int ERROR = 9;
  27.     public static int EOF = 10;
  28.  
  29.     Matcher m;
  30.     String text;
  31.     boolean skipError;
  32.  
  33.  
  34.     public static void main(String[] args) {
  35.     	Lexer lexer = new Lexer("tcu else i34 !!!! 2983 ( + +eqdQ!!!!"); // With some error characters "!" thrown in the middle and at the end
  36.     	for(;;) {
  37.     		Token token = lexer.next();
  38.     		System.out.println(token.tokenNumber + ": " + token.tokenValue);
  39.     		if (token.tokenNumber == EOF)
  40.     			break;
  41.     	}
  42.     }
  43.  
  44.     public Lexer(String text)
  45.     {
  46.  
  47.         String _WHITESPACE = "(\\s+)";
  48.         String _PUNCTUATION = "((?:[+*/-]|:=))";
  49.         String _LPAREN = "(\\()";
  50.         String _RPAREN = "(\\))";
  51.         String _KEYWORD = "(if|then|else|endif|while|do|endwhile|skip)";
  52.         String _IDENTIFIER = "([a-zA-Z][0-9a-zA-Z]*)";
  53.         String _NUMBER = "([0-9)]+)";
  54.         String _SEMICOLON = "(;)";
  55. 		String _ERROR = "(.)"; // must be last and able to capture one character
  56.  
  57.         String regex = String.join("|", _WHITESPACE, _PUNCTUATION, _LPAREN, _RPAREN, _KEYWORD, _IDENTIFIER, _NUMBER, _SEMICOLON, _ERROR);
  58.  
  59.         Pattern p = Pattern.compile(regex);
  60. 		this.text = text;
  61.         m = p.matcher(this.text);
  62. 		skipError = false;
  63.     }
  64.  
  65.     public Token next()
  66.     {
  67.         Token token = null;
  68.     	for(;;) {
  69.             if (!m.find())
  70.                 return new Token(EOF, "<EOF>");
  71. 			for (int tokenNumber = 1; tokenNumber <= 9; tokenNumber++) {
  72. 				String tokenValue = m.group(tokenNumber);
  73. 				if (tokenValue != null) {
  74. 					token = new Token(tokenNumber, tokenValue);
  75. 					break;
  76. 				}
  77. 			}
  78. 			if (token.tokenNumber == ERROR) {
  79. 				if (!skipError) {
  80. 					skipError = true; // we don't want successive errors
  81. 					return token;
  82. 				}
  83. 			}
  84. 			else {
  85. 				skipError = false;
  86. 				if (token.tokenNumber != WHITESPACE)
  87. 					return token;
  88. 			}
  89.         }
  90.     }
  91.  
  92. }
Success #stdin #stdout 0.16s 36680KB
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stdin
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Standard input is empty
stdout
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6: tcu
5: else
6: i34
9: !
7: 2983
3: (
2: +
2: +
6: eqdQ
9: !
10: <EOF>
https://ideone.com/3Yn0Pd
language:
Java (12.0.1)
created:
5 years ago
visibility:
public

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