1 package simpledb.log;
2
3 import static simpledb.file.Page.*;
4 import simpledb.file.Page;
5
6 /**
7 * A class that provides the ability to read the values of
8 * a log record.
9 * The class has no idea what values are there.
10 * Instead, the methods {@link #nextInt() nextInt}
11 * and {@link #nextString() nextString} read the values
12 * sequentially.
13 * Thus the client is responsible for knowing how many values
14 * are in the log record, and what their types are.
15 * @author Edward Sciore
16 */
17 public class BasicLogRecord {
18 private Page pg;
19 private int pos;
20
21 /**
22 * A log record located at the specified position of the specified page.
23 * This constructor is called exclusively by
24 * {@link LogIterator#next()}.
25 * @param pg the page containing the log record
26 * @param pos the position of the log record
27 */
28 public BasicLogRecord(Page pg, int pos) {
29 this.pg = pg;
30 this.pos = pos;
31 }
32
33 /**
34 * Returns the next value of the current log record,
35 * assuming it is an integer.
36 * @return the next value of the current log record
37 */
38 public int nextInt() {
39 int result = pg.getInt(pos);
40 pos += INT_SIZE;
41 return result;
42 }
43
44 /**
45 * Returns the next value of the current log record,
46 * assuming it is a string.
47 * @return the next value of the current log record
48 */
49 public String nextString() {
50 String result = pg.getString(pos);
51 pos += STR_SIZE(result.length());
52 return result;
53 }
54 }