1 import java.io.IOException;
2 import java.io.RandomAccessFile;
3
4 /**
5 This class is a conduit to a random access file
6 containing savings account data.
7 */
8 public class BankData
9 {
10 private RandomAccessFile file;
11
12 public static final int INT_SIZE = 4;
13 public static final int DOUBLE_SIZE = 8;
14 public static final int RECORD_SIZE = INT_SIZE + DOUBLE_SIZE;
15
16 /**
17 Constructs a BankData object that is not associated with a file.
18 */
19 public BankData()
20 {
21 file = null;
22 }
23
24 /**
25 Opens the data file.
26 @param filename the name of the file containing savings
27 account information
28 */
29 public void open(String filename)
30 throws IOException
31 {
32 if (file != null) file.close();
33 file = new RandomAccessFile(filename, "rw");
34 }
35
36 /**
37 Gets the number of accounts in the file.
38 @return the number of accounts
39 */
40 public int size()
41 throws IOException
42 {
43 return (int) (file.length() / RECORD_SIZE);
44 }
45
46 /**
47 Closes the data file.
48 */
49 public void close()
50 throws IOException
51 {
52 if (file != null) file.close();
53 file = null;
54 }
55
56 /**
57 Reads a savings account record.
58 @param n the index of the account in the data file
59 @return a savings account object initialized with the file data
60 */
61 public BankAccount read(int n)
62 throws IOException
63 {
64 file.seek(n * RECORD_SIZE);
65 int accountNumber = file.readInt();
66 double balance = file.readDouble();
67 return new BankAccount(accountNumber, balance);
68 }
69
70 /**
71 Finds the position of a bank account with a given number
72 @param accountNumber the number to find
73 @return the position of the account with the given number,
74 or -1 if there is no such account
75 */
76 public int find(int accountNumber)
77 throws IOException
78 {
79 for (int i = 0; i < size(); i++)
80 {
81 file.seek(i * RECORD_SIZE);
82 int a = file.readInt();
83 if (a == accountNumber) // Found a match
84 return i;
85 }
86 return -1; // No match in the entire file
87 }
88
89 /**
90 Writes a savings account record to the data file
91 @param n the index of the account in the data file
92 @param account the account to write
93 */
94 public void write(int n, BankAccount account)
95 throws IOException
96 {
97 file.seek(n * RECORD_SIZE);
98 file.writeInt(account.getAccountNumber());
99 file.writeDouble(account.getBalance());
100 }
101 }