我正在编写一个银行系统，当用户存入或取出资金时，文本文件中的余额应相应更新。
void saveFiles(int index) throws IOException{
DateFormat dateFormat = new SimpleDateFormat("E MM/dd/yyyy hh:mm:ss a");
Date date = new Date();
BufferedWriter twriter = new BufferedWriter(new FileWriter("Transactions.txt", true));
BufferedWriter fwriter = new BufferedWriter(new FileWriter("Customers.txt", true));
PrintWriter outputFile = new PrintWriter(fwriter);
PrintWriter output = new PrintWriter(twriter);
//update to Customer.txt file
outputFile.println(people[index].getCustID() + "," +people[index].getTitle() + "," +people[index].getfName() + ","+people[index].getlName()+ ","
+people[index].getUsername() + "," +people[index].getPassword() + ","+people[index].getSSN() + ","+people[index].getUniqueID() + ","
+people[index].getSightkey() + ","+ FCA + "," + TSA + "," + people[index].getSoarAcctBal());
//update Transactions.txt file
output.write((dateFormat.format(date) + "," +people[index].getCustID() + "," +numbers[index].getCheckingAcctNum() + "," + transferAmount + "," + "Withdraw" + "," + people[index].getSoarAcctBal()));
outputFile.flush();
outputFile.close();
output.flush();
output.close();
}
加载客户档案
//DEFAULT CONSTRUCTOR
public GEBank() {
people = new Customer[4];
}
//LOAD CUSTOMERS FILE
void loadCustomers() throws IOException, FileNotFoundException, ParseException{
BufferedReader inputFile = new BufferedReader(new FileReader("Customers.txt"));
//String that holds current file line.
String custID = "", title = "", fName = "", lName = "", username = "", password = "", SSN = "", uniqueID = "", sightkey = "",
checkingAcctBal = "", savingsAcctBal = "", soarAcctBal = "", line = "";
//Line number of count
int i = 0;
//Read the first customer
line = inputFile.readLine();
//load the array
while (line != null)
{ //Get each item from the line, stopping at the comma separator
StringTokenizer st = new StringTokenizer(line,",");
//Get each token and store it in the array
custID = st.nextToken();
title = st.nextToken();
fName = st.nextToken();
lName = st.nextToken();
username = st.nextToken();
password = st.nextToken();
SSN = st.nextToken();
uniqueID = st.nextToken();
sightkey = st.nextToken();
checkingAcctBal = st.nextToken();
savingsAcctBal = st.nextToken();
soarAcctBal = st.nextToken();
//Instantiate each customer
people[i] = new Customer(Integer.parseInt(custID), title, fName, lName, username, password,
Integer.parseInt(SSN), uniqueID, sightkey, Float.parseFloat(checkingAcctBal), Float.parseFloat(savingsAcctBal), Float.parseFloat(soarAcctBal));
//Get the next customer
i++;
//System.out.println(username);
//Read the next customer
line = inputFile.readLine();
}
inputFile.close();
//System.out.println("The Customer Info file is loaded.");
}
这是我的transferFunds方法。我以为我可以设置新余额并将该设置余额写入文件，但它不起作用我可能做错了。
//TRANSFER FUNDS METHOD
void transferFunds(int index) throws IOException{
BufferedReader input = new BufferedReader(new InputStreamReader(System.in));
DateFormat dateFormat = new SimpleDateFormat("E MM/dd/yyyy hh:mm:ss a");
Date date = new Date();
int transferchoice = -1;
do{
System.out.println("\n-- TRANSFER FUNDS MENU --\n");
//transfer from checking to savings
System.out.println("1: Checking Account to Savings Account");
//transfer from savings to checking
System.out.println("2: Savings Account to Checking Account");
System.out.println("\nMake a selection from the above menu options: ");
transferchoice = Integer.parseInt(input.readLine());
//show account numbers of customer
System.out.println("\n-- ACCOUNT NUMBERS --\n");
System.out.println("Checking Account Number: "+numbers[index].getCheckingAcctNum());
System.out.println("Savings Account Number: "+numbers[index].getSavingsAcctNum());
//show account balances of customer
System.out.println("\n-- CURRENT BALANCE --\n");
System.out.println("Checking Account Balance: $"+people[index].getCheckingAcctBal()+".");
System.out.println("Savings Account Balance: $"+people[index].getSavingsAcctBal()+".");
System.out.println("\nHow much would you like to transfer?");
transferAmount = Float.parseFloat(input.readLine());
System.out.println("\nBusiness Date & Time: " + dateFormat.format(date));
//FROM CHECKING TO SAVINGS ACCOUNT
FCA = (people[index].getCheckingAcctBal() - transferAmount);
TSA = (people[index].getSavingsAcctBal() + transferAmount);
//FROM SAVINGS TO CHECKING ACCOUNT
FSA = (people[index].getSavingsAcctBal() - transferAmount);
TCA = (people[index].getCheckingAcctBal() + transferAmount);
saveFiles(index);
if(transferchoice == 1){
System.out.println("\nYou've chosen to transfer $" +transferAmount+ " from your Checking Account to your Savings Account.\n"
+ "\n-- UPDATED BALANCE --\n"
+ "\nChecking Account Balance: $"+FCA+//money[index].setCheckingAcctBal(FCA)
"\nSavings Account Balance: $"+TSA+""
+ "\nFunds successfully transferred"); //confirm the transaction
}else if(transferchoice == 2){
System.out.println("\nYou've chosen to transfer $" +transferAmount+ " from your Savings Account to your Checking Account.\n"
+ "\n-- UPDATED BALANCE --\n"
+ "\nChecking Account Balance: $"+FSA+
"\nSavings Account Balance: $"+TCA+""
+ "\nFunds successfully transferred"); //confirm the transaction
}
if(people[index].getCheckingAcctBal() < transferAmount && people[index].getSavingsAcctBal() < transferAmount){
System.out.println("We're sorry, you do not have sufficient funds to complete this transaction. Transaction Cancelled.\n\n");
return;
}
//Ask customer if they would like to view another balance
System.out.print("\nDo you want to make another transfer? [Enter y/n]: ");
moretransfers = input.readLine().charAt(0);
}while (moretransfers == 'Y' || moretransfers == 'y');
//If moretransfers is no, then show displayLoginMenu method
if (moretransfers == 'N' || moretransfers == 'n')
{ displayLoginMenu(index);}
}
以下是用户将$ 400.00从一个帐户转移到另一个帐户后的附加文本文件。它创造了最后一行。我想要它做的是找到这条线＆＃34;人[索引]＆＃34;然后用更新的输出
替换它100,Ms,Jane,Doe,10ann,guy,1234,brunch,yellow,20000.00,5000.00,2000.00
101,Mr,John,Smith,1mark,girl,2345,lunch,gray,10000.00,3000.00,6000.00
102,Ms,Jenaya,Joseph,2jjPM,jj2,6789,breakfast,green,40000.00,20000.00,80000.00
103,Mr,Edward,Donkor,05001,1005,5432,dinner,blue,25000.00,7100.00,8000.00
101,Mr,John,Smith,1mark,girl,2345,lunch,gray,9600.0,3400.0,6000.0
任何人都可以帮忙吗？我一直在研究，我发现你可以创建一个临时文件，然后将信息覆盖到一个新文件中。但我仍然不确定如何做到这一点。我还是Java新手，所以任何帮助都会受到赞赏。
答案 0 :(得分：2)
如何从JAVA中的文本文件更新一行？
你没有。
不是Java，不是C语言，不是C＃，不是Python，不是Ruby，不是perl，不是Brainfuck。不是任何语言。
内联修改文本文件是一个万无一失的保证，您无法告诉将要发生的事情，但在（100 - epsilon）％的情况下，epsilon 非常接近0 ，你将至少丢失文件的原始内容
。将修改后的内容写入新文件，然后以原子方式重命名为旧文件。幸运的是，java.nio.file为你提供了StandardCopyOption.ATOMIC_MOVE。
（你仍然可以使用FileChannel.map() mmap（）文件;但这通常只对具有固定大小记录的文件进行;这不是文本文件。提醒根据您使用的编码，相同的字符可能会超过一个字节。）
答案 1 :(得分：-1)
呃，如果它有帮助，你可以看看这个。易于阅读。
public class ExampleTextEdit {
public static String APPLICATION_LOCATION;
public static File textFile;
public static BufferedReader reader;
public static void main(String[] args) {
APPLICATION_LOCATION = ExampleTextEdit.class.getProtectionDomain()
.getCodeSource().getLocation().getPath();
textFile = new File(APPLICATION_LOCATION + File.separator
+ "mytextfile.txt");
try {
if ( !textFile.exists()) {
textFile.createNewFile();
BufferedWriter writer = new BufferedWriter(new FileWriter(
textFile));
for (int i = 0; i < 20; i++) {
writer.write("this that " + i);
writer.newLine();
}
writer.flush();
writer.close();
} else {
loadText();
File f = new File(APPLICATION_LOCATION + File.separator + "temp.txt");
f.createNewFile();
String temp;
BufferedWriter writeNew = new BufferedWriter(new FileWriter(f));
reader = new BufferedReader(new FileReader(textFile));
while ((temp = reader.readLine()) != null) {
if (temp.contains("" + 14))
writeNew.write("lol changed");
else
writeNew.write(temp);
writeNew.newLine();
}
writeNew.flush();
writeNew.close();
reader.close();
textFile.delete();
f.renameTo(textFile);
}
} catch (Exception e) {
e.printStackTrace();
}
}
public static void loadText() throws Exception {
String line;
reader = new BufferedReader(new FileReader(textFile));
while ((line = reader.readLine()) != null) {
System.out.println(line);
}
}
}
你不需要太过花哨的东西，直到你更熟悉图书馆坚持你所知道的东西。
答案 2 :(得分：-1)
我可能已经弄清楚了。
void saveFiles(int index) throws IOException{
BufferedReader br = new BufferedReader(new FileReader(new File("Customers.txt")));
String uname = people[index].getUsername();
String line = null;
StringBuilder sb =new StringBuilder();
while ((line = br.readLine())!=null)
{
if(line.indexOf(uname)!=-1)
{
//do your logic here
sb.append(people[index].getCustID() + "," +people[index].getTitle() + "," +people[index].getfName() + ","+people[index].getlName()+ ","
+people[index].getUsername() + "," +people[index].getPassword() + ","+people[index].getSSN() + ","+people[index].getUniqueID() + ","
+people[index].getSightkey() + ","+ FCA + "," + TSA + "," + people[index].getSoarAcctBal() +"\n");
}else{
sb.append(line+"\n");
}
}
br.close();
BufferedWriter bw = new BufferedWriter(new FileWriter(new File("Customers.txt")));
PrintWriter out = new PrintWriter(bw);
out.print(sb.toString());
out.flush();
out.close();
}
但我的输出现在是这样的：
100,Ms,Jane,Doe,10ann,guy,1234,brunch,yellow,20000.00,5000.00,2000.00101,Mr,John,Smith,1mark,girl,2345,lunch,gray,9600.0,3400.0,6000.0102,Ms,Jenaya,Joseph,2jjPM,jj2,6789,breakfast,green,40000.00,20000.00,80000.00103,Mr,Edward,Donkor,05001,1005,5432,dinner,blue,25000.00,7100.00,8000.00
如何将每个实例打印到新行？