1
2
3 package net.sourceforge.pmd.ast;
4
5 /**
6 * This interface describes a character stream that maintains line and
7 * column number positions of the characters. It also has the capability
8 * to backup the stream to some extent. An implementation of this
9 * interface is used in the TokenManager implementation generated by
10 * JavaCCParser.
11 *
12 * All the methods except backup can be implemented in any fashion. backup
13 * needs to be implemented correctly for the correct operation of the lexer.
14 * Rest of the methods are all used to get information like line number,
15 * column number and the String that constitutes a token and are not used
16 * by the lexer. Hence their implementation won't affect the generated lexer's
17 * operation.
18 */
19
20 public interface CharStream {
21
22 /**
23 * Returns the next character from the selected input. The method
24 * of selecting the input is the responsibility of the class
25 * implementing this interface. Can throw any java.io.IOException.
26 */
27 char readChar() throws java.io.IOException;
28
29 /**
30 * Returns the column position of the character last read.
31 * @deprecated
32 * @see #getEndColumn
33 */
34 int getColumn();
35
36 /**
37 * Returns the line number of the character last read.
38 * @deprecated
39 * @see #getEndLine
40 */
41 int getLine();
42
43 /**
44 * Returns the column number of the last character for current token (being
45 * matched after the last call to BeginTOken).
46 */
47 int getEndColumn();
48
49 /**
50 * Returns the line number of the last character for current token (being
51 * matched after the last call to BeginTOken).
52 */
53 int getEndLine();
54
55 /**
56 * Returns the column number of the first character for current token (being
57 * matched after the last call to BeginTOken).
58 */
59 int getBeginColumn();
60
61 /**
62 * Returns the line number of the first character for current token (being
63 * matched after the last call to BeginTOken).
64 */
65 int getBeginLine();
66
67 /**
68 * Backs up the input stream by amount steps. Lexer calls this method if it
69 * had already read some characters, but could not use them to match a
70 * (longer) token. So, they will be used again as the prefix of the next
71 * token and it is the implemetation's responsibility to do this right.
72 */
73 void backup(int amount);
74
75 /**
76 * Returns the next character that marks the beginning of the next token.
77 * All characters must remain in the buffer between two successive calls
78 * to this method to implement backup correctly.
79 */
80 char BeginToken() throws java.io.IOException;
81
82 /**
83 * Returns a string made up of characters from the marked token beginning
84 * to the current buffer position. Implementations have the choice of returning
85 * anything that they want to. For example, for efficiency, one might decide
86 * to just return null, which is a valid implementation.
87 */
88 String GetImage();
89
90 /**
91 * Returns an array of characters that make up the suffix of length 'len' for
92 * the currently matched token. This is used to build up the matched string
93 * for use in actions in the case of MORE. A simple and inefficient
94 * implementation of this is as follows :
95 *
96 * {
97 * String t = GetImage();
98 * return t.substring(t.length() - len, t.length()).toCharArray();
99 * }
100 */
101 char[] GetSuffix(int len);
102
103 /**
104 * The lexer calls this function to indicate that it is done with the stream
105 * and hence implementations can free any resources held by this class.
106 * Again, the body of this function can be just empty and it will not
107 * affect the lexer's operation.
108 */
109 void Done();
110
111 }
112