Java Reference
In-Depth Information
Enter request
1 - List accounts with zero balances
2 - List accounts with credit balances
3 - List accounts with debit balances
4 - Terminate program
?
3
Accounts with debit balances:
100 Bob Blue 24.98
500 Sue Yellow 224.62
Enter request
1 - List accounts with zero balances
2 - List accounts with credit balances
3 - List accounts with debit balances
4 - Terminate program
?
4
Fig. 15.8
|
Credit-inquiry program. (Part 4 of 4.)
The record information is collected by reading through the file and determining if
each record satisfies the criteria for the selected account type. Line 18 in
main
calls method
getRequest
(lines 41-68) to display the menu options, translates the number typed by the
user into a
MenuOption
and stores the result in
MenuOption
variable
accountType
. Lines
20-37 loop until the user specifies that the program should terminate. Lines 22-33 display
a header for the current set of records to be output to the screen. Line 35 calls method
readRecords
(lines 71-97), which loops through the file and reads every record.
Method
readRecords
uses a
try
-with-resources statement (introduced in
Section 11.12) to create a
Scanner
that opens the file for reading (line 74)—recall that
try
-with-resources will close its resource(s) when the
try
block terminates successfully or
due to an exception. The file will be opened for reading with a new
Scanner
object each
time
readRecords
is called, so that we can again read from the beginning of the file. Lines
78-81 read a record. Line 84 calls method
shouldDisplay
(lines 100-111) to determine
whether the current record satisfies the account type requested. If
shouldDisplay
returns
true
, the program displays the account information. When the
end-of-file marker
is
reached, the loop terminates and the
try
-with-resources statement closes the
Scanner
and
the file. Once all the records have been read, control returns to
main
and
getRequest
is
again called (line 36) to retrieve the user's next menu option.
The data in many sequential files cannot be modified without the risk of destroying other
data in the file. For example, if the name “
White
” needs to be changed to “
Worthington
,”
the old name cannot simply be overwritten, because the new name requires more space.
The record for
White
was written to the file as
300 Pam White 0.00
