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