|
1
3 package org.jmock.examples.calculator;
4
5 import java.io.IOException  ;
6 import java.io.PushbackReader ;
7 import java.io.Reader ;
8 import java.io.StringReader ;
9 import java.util.Stack ;
10
11
12 public class Lexer
13 {
14 private static final int END_OF_STREAM = -1;
15 private static final char DECIMAL_PLACE = '.';
16
17 private PushbackReader input;
18 private StringBuffer tokenValue = new StringBuffer ();
19 private Stack pushBack = new Stack ();
20
21 public Lexer( Reader input ) {
22 this.input = new PushbackReader (input);
23 }
24
25 public Lexer( String inputString ) {
26 this(new StringReader (inputString));
27 }
28
29 public void pushBack( Token token ) {
30 pushBack.push(token);
31 }
32
33 public Token nextToken() throws IOException , ParseException {
34 if (pushBack.isEmpty()) {
35 return readToken();
36 }
37 return (Token)pushBack.pop();
38 }
39
40 private Token readToken() throws IOException , ParseException {
41 tokenValue.setLength(0);
42
43 skipWhitespace();
44
45 int ch = peekChar();
46
47 if (ch == END_OF_STREAM) {
48 return new Token(Token.END, null);
49 } else if (isDigit(ch)) {
50 return readNumber();
51 } else if (isIdentifierStart(ch)) {
52 return readIdentifier();
53 } else {
54 return readOperator();
55 }
56 }
57
58 public void skipWhitespace() throws IOException {
59 int ch;
60
61 do {
62 ch = readChar();
63 }
64 while (ch != END_OF_STREAM && Character.isWhitespace((char)ch));
65
66 unreadChar(ch);
67 }
68
69 private boolean isDigit( int ch ) {
70 return ch != END_OF_STREAM && Character.isDigit((char)ch);
71 }
72
73 private Token readNumber() throws IOException {
74 collectDigits();
75 if (peekChar() == DECIMAL_PLACE) {
76 tokenValue.append((char)readChar());
77 collectDigits();
78 }
79
80 return createToken(Token.NUMBER);
81 }
82
83 private void collectDigits() throws IOException {
84 int ch;
85
86 while (isDigit(ch = readChar())) {
87 tokenValue.append((char)ch);
88 }
89
90 unreadChar(ch);
91 }
92
93 private boolean isIdentifierStart( int ch ) {
94 return Character.isUnicodeIdentifierStart((char)ch);
95 }
96
97 private boolean isIdentifierPart( int ch ) {
98 return ch != -1 && Character.isUnicodeIdentifierPart((char)ch);
99 }
100
101 private Token readIdentifier() throws IOException {
102 tokenValue.append((char)readChar());
103
104 int ch;
105 while (isIdentifierPart((ch = readChar()))) {
106 tokenValue.append((char)ch);
107 }
108 unreadChar(ch);
109
110 return createToken(Token.IDENTIFIER);
111 }
112
113 private Token readOperator() throws IOException , ParseException {
114 int ch = readChar();
115 tokenValue.append((char)ch);
116
117 switch (ch) {
118 case '+':
119 return createToken(Token.ADD);
120 case '-':
121 return createToken(Token.SUBTRACT);
122 case '*':
123 return createToken(Token.MULTIPLY);
124 case '/':
125 return createToken(Token.DIVIDE);
126 case '^':
127 return createToken(Token.POWER);
128 case '(':
129 return createToken(Token.PAREN_OPEN);
130 case ')':
131 return createToken(Token.PAREN_CLOSE);
132
133 default:
134 throw new ParseException("unrecognised character '" + (char)ch + "'");
135 }
136 }
137
138
139 private Token createToken( int tokenType ) {
140 return new Token(tokenType, tokenValue.toString());
141 }
142
143 private int peekChar() throws IOException {
144 int ch = readChar();
145 unreadChar(ch);
146 return ch;
147 }
148
149 private int readChar() throws IOException {
150 return input.read();
151 }
152
153 private void unreadChar( int ch ) throws IOException {
154 if (ch != END_OF_STREAM) input.unread(ch);
155 }
156 }
157 |
Popular Tags |
Java API By Example, From Geeks To Geeks.