diff options
author | Maël Gassmann <mael.gassmann@students.bfh.ch> | 2021-06-11 01:39:49 +0200 |
---|---|---|
committer | Maël Gassmann <mael.gassmann@students.bfh.ch> | 2021-06-11 01:39:49 +0200 |
commit | 126a6c85b60ad07fa29ab48315f0f195fb45d854 (patch) | |
tree | 1c0245fc232c701da8577a5451d703a0d5808822 /calculator-java/src/main/java/ch/bfh/CalculatorLexer.java | |
parent | ee369b50b14ffe662e05355459f57c076680cd58 (diff) |
[+] First version of the java calculator
Diffstat (limited to 'calculator-java/src/main/java/ch/bfh/CalculatorLexer.java')
-rw-r--r-- | calculator-java/src/main/java/ch/bfh/CalculatorLexer.java | 106 |
1 files changed, 106 insertions, 0 deletions
diff --git a/calculator-java/src/main/java/ch/bfh/CalculatorLexer.java b/calculator-java/src/main/java/ch/bfh/CalculatorLexer.java new file mode 100644 index 0000000..ba10944 --- /dev/null +++ b/calculator-java/src/main/java/ch/bfh/CalculatorLexer.java @@ -0,0 +1,106 @@ +package ch.bfh; +import ch.bfh.exceptions.LexerException; + +// Lexer for classical arithmetic expressions with identifiers and assignments. +// Scans a source string char by char. + +public class CalculatorLexer { + + private String src; // source string for lexical analysis + private int idx; // current index in source + private int len; // length of source + + public CalculatorLexer() { } + + public void initLexer(String source) { + this.src = source; + idx = 0; + len = src.length(); + } + + // Consumes letters only and builds an identifier + private String identifier() { + StringBuffer s = new StringBuffer(); + + do { + s.append(src.charAt(idx)); + idx++; + } while (idx < len && Character.isLetter(src.charAt(idx))); + return s.toString(); + } + + // Consumes digits and convert integer part and decimal part + // Convert characters using the formula + // "3456.253" = [(((3+0)*10+4)*10+5)*10+6]+[0.1*2+0.01*5+0.001*3] + private double number() throws LexerException { + double v = 0; // accumulates the result + double factor = 0.1; // factor for decimal part + + do { // integer part + v = v * 10 + Character.digit(src.charAt(idx),30); + idx++; + } while (idx < len && Character.isDigit(src.charAt(idx))); + if (idx < len && src.charAt(idx) == '.') { // decimal point + idx++; + if (idx < len && Character.isDigit(src.charAt(idx))) { // decimal part + while (idx < len && Character.isDigit(src.charAt(idx))) { + v = v + (factor * Character.digit(src.charAt(idx),30)); + factor = factor * 0.1; + idx++; + } + } + else throw new LexerException("Illegal number: decimal part missing"); + } + return v; + } + + // Skips blanks, tabs, newlines + private void skip() { + char c; + while (idx < len) { + c = src.charAt(idx); + if (c==' ' || c=='\t' || c=='\n') idx++; + else break; + } + } + + // returns next token + public Token nextToken() throws LexerException { + Token tok = new Token(); + + skip(); + if (idx>=len) { + tok.str="EOL"; + tok.type=Token.EOL; + } + else + // is it a positive number? + if (Character.isDigit(src.charAt(idx))) { + tok.value = number(); + tok.type = Token.NUM; + tok.str = Double.toString(tok.value); + } + else + if (Character.isLetter(src.charAt(idx))) { + tok.value = 0; + tok.type = Token.ID; + tok.str = identifier(); + if (tok.str.compareTo("let")==0) tok.type = Token.LET; + if (tok.str.compareTo("exit")==0) tok.type = Token.END; + } + else { + switch (src.charAt(idx)) { + case '+': tok.type = Token.ADD; tok.str = "+"; break; + case '-': tok.type = Token.SUB; tok.str = "-"; break; + case '*': tok.type = Token.MUL; tok.str = "*"; break; + case '/': tok.type = Token.DIV; tok.str = "/"; break; + case '(': tok.type = Token.PAL; tok.str = "("; break; + case ')': tok.type = Token.PAR; tok.str = ")"; break; + case '=': tok.type = Token.EQU; tok.str = "="; break; + default : throw new LexerException("Illegal Token: '" + src.charAt(idx) + "'"); + } + idx++; + } + return tok; + } +}
\ No newline at end of file |