Java 数据类型字符串的大型数组
我希望大家都过得很好。我对这个开发人员的东西还是新手，虽然我觉得它非常有趣，但我开始明白如果你不跟踪你正在做的事情，它会变得多么乏味。我正在更新一个模拟ATM程序。新版本读取.txt文件以验证帐户信息。验证后，您可以检查余额、存款、取款或注销。一旦您进行了交易，该程序将使用该帐户的更新余额更新旧的.txt文件。我终于让所有的东西都像预期的那样工作了，但是当我回去检查更新的.txt文件时，那个特定的帐户被更新了，但是文件中的其余字符串被更新为null，我不知道为什么以及是什么导致我的程序这样做。我觉得问题出在更新方法上，我忽略了一些东西。下面你可以看到我的源代码，下面是我得到的输出。任何关于这一错误背后逻辑的解释都将不胜感激Java 数据类型字符串的大型数组,java,arrays,iostream,Java,Arrays,Iostream,我希望大家都过得很好。我对这个开发人员的东西还是新手，虽然我觉得它非常有趣，但我开始明白如果你不跟踪你正在做的事情，它会变得多么乏味。我正在更新一个模拟ATM程序。新版本读取.txt文件以验证帐户信息。验证后，您可以检查余额、存款、取款或注销。一旦您进行了交易，该程序将使用该帐户的更新余额更新旧的.txt文件。我终于让所有的东西都像预期的那样工作了，但是当我回去检查更新的.txt文件时，那个特定的帐户被更新了，但是文件中的其余字符串被更新为null，我不知道为什么以及是什么导致我的程序这样做。我
import java.util.*;
import java.io.*;
public class ATM2 {
public static Scanner kbd = new Scanner(System.in);
/*
* This method reads the number of lines in the .txt file
* and returns the array size.
*/
public static int arraySize () {
int result = 0;
try
{
Scanner lineReader = new Scanner(new FileReader("ATMData.txt"));
int lineCount=0;
while(lineReader.hasNextLine())
{
String size;
size = lineReader.nextLine();
lineCount++;
}
lineReader.close();
return lineCount;
}
catch(FileNotFoundException e)
{
System.out.println("ERROR: FILE NOT FOUND");
return result;
}
}
//Method searches .txt file and returns String
//array with all account info.
public static String[] acctLine(int size){
String[] validAccounts = null;
try
{
Scanner lineReader = new Scanner(new FileReader("ATMData.txt"));
int lineCount=0;
String [] acctNums= new String[size];
while(lineReader.hasNextLine())
{
String lineInfo;
lineInfo = lineReader.nextLine();
acctNums[lineCount]=lineInfo;
lineCount++;
}
lineReader.close();
return acctNums;
}
catch(FileNotFoundException e)
{
System.out.println("ERROR: FILE NOT FOUND");
return validAccounts;
}
}
//Method updates the txt file with new acct information.
public static void acctUpdate (String[] validAccount, String fileName){
try
{
PrintWriter newFile = new PrintWriter(new FileWriter(fileName));
for(int i=0; i<validAccount.length; i++){
newFile.println(validAccount[i]);
}
newFile.close();
}
catch(Exception e){
System.out.println("ERROR: FILE NOT PRINTED");
}
}
/*The checkID method determines if acctNum is a valid account number
* and pwd is the correct password for the account. If the account information
* is valid, the method returns the current account balance, as a string.
* If the account information is invalid, the method returns the string "error"
*/
public static String checkID(String acctNum, String pwd, String [] validAccounts)
{
String result = "ERROR";
String acctString = "ERROR";
boolean foundIt = false;
for(int i=0; i<validAccounts.length; i++) //Loop compares the input data with array data.
{
acctString = validAccounts[i];
if (acctNum.equals(acctString.substring(0, acctString.indexOf(" "))) &&
pwd.equals(acctString.substring(acctString.indexOf(" ")+1,acctString.lastIndexOf(" ")))){
foundIt = true;
result = acctString.substring(acctString.lastIndexOf(" ") + 1);
}
}
if (foundIt) //If it's true it returns the acct. balance.
{
return result;
}
else
{
System.out.println("ERROR: INVALID ACCOUNT TYPE");
}
return result;
}
/* This method finds the array index of the desired account string.
* and returns the the index of the line
*/
public static int arrayIndex(String acctNum, String pwd, String [] validAccounts)
{
int accountPos=0;
Boolean foundIt = false;
//loop searches for the index of the array.
for(accountPos=0; accountPos<validAccounts.length && !foundIt; accountPos++)
{
if (acctNum.equals(validAccounts[accountPos].substring(0, validAccounts[accountPos].indexOf(" "))) &&
pwd.equals(validAccounts[accountPos].substring(validAccounts[accountPos].indexOf(" ")+1, validAccounts[accountPos].lastIndexOf(" "))))
{
foundIt = true;
}
}
return accountPos;
}
/*Method creates menu options and returns
*the choice selected by the user.
*/
public static int menu()
{
int menuChoice;
do
{
System.out.print("\nENTER TRANSACTION TYPE: CHOOSE 1-4."
+ " \n 1. Display Balance"
+ "\n 2. Deposit\n 3. Withdraw\n 4. Log Out\n");
menuChoice = kbd.nextInt();
if (menuChoice < 1 || menuChoice > 4){
System.out.println("error");
}
}while (menuChoice < 1 || menuChoice > 4);
return menuChoice;
}
/*Method displays the balance to the screen.
*/
public static void displayBalance(double balance)
{
System.out.printf("\nYOUR NEW BALANCE IS: $%.2f\n", balance);
}
/*Method calculates the deposit going in to account.
Returns the total deposit.
*/
public static double deposit(double orgBal, double depAmt)
{
return orgBal + depAmt;
}
/*Method that calculates the balance after the withdraw.
* returns a double with the amount withdrawn.
*/
public static double withdraw(double orgBal, double wdrlAmt)
{
if (wdrlAmt > orgBal)
{
return orgBal;
}
else
{
return orgBal-wdrlAmt;
}
}
public static void main(String[] args) {
String accNum, pass, fileName="ATMData.txt", origBal = "ERROR";
String acctInfo;
int count = 0, menuOption = 0, acctPos;
double depositAmt, withdrawAmt, currentBal;
String [] validAccounts =acctLine(arraySize());
/*loop that will count the number of login attempts
*you make and will exit program if it is more than 3.
*as long as oriBal equals an error.
*/
do{
System.out.println("PLEASE ENTER YOUR ACCOUNT NUMBER: ");
accNum = kbd.next();
System.out.println("ENTER YOUR PASSWORD: ");
pass = kbd.next();
origBal = checkID(accNum, pass, validAccounts);
count++;
acctPos = arrayIndex(accNum, pass, validAccounts)-1;
if (count >= 3 && origBal.equals("ERROR:")){
System.out.print("MAX LOGIN ATTEMPTS REACHED.");
System.exit(0);
}
else if (!(origBal.equals("ERROR"))){
System.out.println("\nYOUR CURRENT BALANCE IS: $ "+ origBal);
}
else
System.out.println(origBal);
}while(origBal.equals("ERROR"));
currentBal=Double.parseDouble(origBal);
/*this loop will keep track of the options that
*the user inputs in for the menu. and will
*give the option of deposit, withdraw, or logout.
*/
while (menuOption != 4)
{
menuOption=menu();
switch (menuOption)
{
case 1:
displayBalance(currentBal);
break;
case 2:
System.out.print("HOW MUCH DO WISH TO DEPOSIT: $ ");
depositAmt = kbd.nextDouble();
currentBal = deposit(depositAmt, currentBal);
displayBalance(currentBal);
break;
case 3:
System.out.print("HOW MUCH DO YOU WISH TO WITHDRAW: $ ");
withdrawAmt = kbd.nextDouble();
if (withdrawAmt > currentBal)
System.out.println("ERROR: YOU DON'T HAVE ENOUGH FUNDS TO COMPLETE"
+ " TRANSACTION."
+ " ENTER TRANSACTION TYPE: CHOOSE 1-4");
currentBal = withdraw(currentBal, withdrawAmt);
displayBalance(currentBal);
break;
case 4://Last option logs user out after it updates the ATMData.txt
acctInfo = accNum + " " + pass + " " + String.valueOf(currentBal);
validAccounts[acctPos]=acctInfo;
acctUpdate(validAccounts, fileName);
System.out.println("LOGOUT SUCCESSFULL.");
System.exit(0);
break;
default:
}
}
}
}
7560640 6Z[NVoee1S6 4424.43
04569505 f:H>wAr@<URH 4211.42
528859 ][[79_W?]=:< 724.26
973335820 Si>G7QMp?>e 3207.28
79154675 Y>vfTYwHm0J 3327.47
5554284 6n[^PwZUZlH 1028.66
58773836 28vcgSpwA01 3131.02
95873039 @4XwrN`T9 2598.28
1034703 n@HKk`mTar2Z 1176.75
10192851 X>ATvaR:qT 3857.89
417927608 ;6FYE5l`LPX@ 3401.13
143260 s2UgJtSHYFmn 378.68
34729802 rh\<3rmk7Dm< 255.48
277791753 BR2=siCDi 345.75
1014748 PK?KTMjA63e 1196.16
496714922 M1=I`ve;Wjw 501.26
654156 AB`6cvO0ql: 4310.51
898250859 t^D90Nw?Ii 3876.05
971750 [9q_5AuLlJ 135.97
796678134 KwV^03p:WW=< 3453.65
39482807 C5?H?b9UplL 4109.48
401599 MvHL7Yv07bW 4356.96
8321377 Jc:<_ke9B: 930.90
152773 VQ6\[2k:uoj 3265.93
624426519 kralkKKEia3 4858.39
650002 Km2t\R3>3@G 1470.78
004509766 _0S`1qb^V 1332.24
0274647 WDhg3\p]w 3147.50
974502771 Q4GT<_s3D9CK 4464.22
281866 c_1F]@RpV^ 2952.03
381121 rOo?CiA[kwTs 4555.21
1549064 F7^eh=njp\r 430.24
841319 IBe^GTLGv 4050.76
6499423 tW9>r[s_<\ 1418.09
8579740 cdB12UrLU 2905.74
33581232 <os4;WcEqb 2455.32
725175174 nWjIeFLK3E 3118.08
592410029 RqgPT382p2Lk 3863.32
08274516 DDr?^vuNQ 1630.37
808471 Ow:8udlBrYP 2590.05
769854 0`lpWGrMkrG 2643.59
3591827 MmThLS1DdL5 2715.30
9001605 \n;rMknh7C 4074.83
10345766 N>^qBqhk?39J 539.43
504385 j0Rq=li0c^ 253.77
362335041 >^VN5oh?OSR 324.19
5728008 QZ>BZhGEv 4441.67
26102273 1XCWR;W?^b\ 4203.51
3317249 dmjLKbgZ? 1958.44
793249 5J>ApQZAB 1906.46
536461203 CP5U:f5\d[_p 3742.25
030298042 VBtHo909;QM 986.28
6111228 mmPgiDMALt 1348.95
621992 r7UmSJ\9j 1440.22
310072768 B1ccagCH3 4755.56
819894803 IXfcY9PZG1 4399.39
362945795 5LAdX_s^G 3624.28
99929088 `oHijc^J0u 4507.69
821671 s@OV>NYlacV 4125.72
72368663 Mi?wTcZ_@I 2845.24
22692406 uT05^2plu 2530.73
343817 pB;Glu5sVb7P 2168.28
5138360 877<cT4T;t 1562.15
7560640 6Z[NVoee1S6 4424.43
04569505 f:H>wAr@G7QMp？>e 3207.28
79154675 Y>vfTYwHm0J 3327.47
5554284 6n[^PwZUZlH 1028.66
58773836 28vcgSpwA01 3131.02
95873039@4XwrN`T9 2598.28
1034703n@HKk`mTar2Z 1176.75
10192851 X>ATvaR:qT 3857.89
417927608；第六个FYE5L`LPX@3401.13
143260 s2UgJtSHYFmn 378.68
34729802 rh\BZhGEv 4441.67
26102273 1XCWR；W^b\4203.51
3317249 dmjLKbgZ？1958.44
793249 5J>ApQZAB 1906.46
536461203 CP5U:f5\d[_p3742.25
030298042 VBtHo909；质量管理986.28
611128 mmPgiDMALt 1348.95
621992 r7UmSJ\9j 1440.22
310072768 B1ccagCH3 4755.56
819894803 IXfcY9PZG1 4399.39
362945795 5LAdX\U s^G 3624.28
99929088`oHijc^J0u 4507.69
821671s@OV>NYlacV 4125.72
72368663英里？wTcZ_ui@2845.24
22692406 uT05^2plu 2530.73
343817铅；Glu5sVb7P 2168.28
5138360 877您从未将以前的帐户数据写入validAccounts
。当您运行String[]validAccounts=new String[arraySize（）]；
所有字符串实例都设置为null，只有在更新帐户时才会更改。您需要做的是启动程序时，将现有文本文件读入该字符串数组，然后只更改需要更改的条目。完成后，将字符串数组写入该文件。在主方法中
String[]validAccounts=新字符串[arraySize（）]；
这意味着您有一个空值数组，您需要在这里而不是在另一个方法中分配值数据，因为当您传递数组时，您传递的是对此数组的引用，而不是数据本身
所以在arrayIndex中
validAccounts=acktline（arraySize（））；将把数据放在这个方法中，当它返回时，这个数据将被丢弃。
您需要分配数据一次，然后传递数据，而不在方法中写入数据
e、 g.大体上
String[]validAccounts=新字符串[arraySize（）]；
应该是
字符串[]validAccounts=acktline（arraySize（））；
您不需要在arrayIndex或checkID中再次读取它。
因此，读取一次并存储它，将此数据传递给该方法并从该数据中读取，而不是从新文件中读取
一个简单的例子是这样的-您将看到a=new int…。在原始方法中不会更改a，但在DoesMething中会更改赋值
公共静态void main（字符串[]args）{
非常感谢你，它起了作用，你解释逻辑错误的方式使调整变得相当简单。我希望我能找一位CS教授来解释和教授它。我已经用这些更改更新了期末考试。虽然这对我正在做的工作有效，但你会建议什么可以提高更新代码的效率？同样，我是新手o这一点，我觉得我从你们仁慈的贡献者身上学到了很多。
7560640 6Z[NVoee1S6 4424.43
04569505 f:H>wAr@<URH 4211.42
528859 ][[79_W?]=:< 724.26
973335820 Si>G7QMp?>e 3207.28
79154675 Y>vfTYwHm0J 3327.47
5554284 6n[^PwZUZlH 1028.66
58773836 28vcgSpwA01 3131.02
95873039 @4XwrN`T9 2598.28
1034703 n@HKk`mTar2Z 1176.75
10192851 X>ATvaR:qT 3857.89
417927608 ;6FYE5l`LPX@ 3401.13
143260 s2UgJtSHYFmn 378.68
34729802 rh\<3rmk7Dm< 255.48
277791753 BR2=siCDi 345.75
1014748 PK?KTMjA63e 1196.16
496714922 M1=I`ve;Wjw 501.26
654156 AB`6cvO0ql: 4310.51
898250859 t^D90Nw?Ii 3876.05
971750 [9q_5AuLlJ 135.97
796678134 KwV^03p:WW=< 3453.65
39482807 C5?H?b9UplL 4109.48
401599 MvHL7Yv07bW 4356.96
8321377 Jc:<_ke9B: 930.90
152773 VQ6\[2k:uoj 3265.93
624426519 kralkKKEia3 4858.39
650002 Km2t\R3>3@G 1470.78
004509766 _0S`1qb^V 1332.24
0274647 WDhg3\p]w 3147.50
974502771 Q4GT<_s3D9CK 4464.22
281866 c_1F]@RpV^ 2952.03
381121 rOo?CiA[kwTs 4555.21
1549064 F7^eh=njp\r 430.24
841319 IBe^GTLGv 4050.76
6499423 tW9>r[s_<\ 1418.09
8579740 cdB12UrLU 2905.74
33581232 <os4;WcEqb 2455.32
725175174 nWjIeFLK3E 3118.08
592410029 RqgPT382p2Lk 3863.32
08274516 DDr?^vuNQ 1630.37
808471 Ow:8udlBrYP 2590.05
769854 0`lpWGrMkrG 2643.59
3591827 MmThLS1DdL5 2715.30
9001605 \n;rMknh7C 4074.83
10345766 N>^qBqhk?39J 539.43
504385 j0Rq=li0c^ 253.77
362335041 >^VN5oh?OSR 324.19
5728008 QZ>BZhGEv 4441.67
26102273 1XCWR;W?^b\ 4203.51
3317249 dmjLKbgZ? 1958.44
793249 5J>ApQZAB 1906.46
536461203 CP5U:f5\d[_p 3742.25
030298042 VBtHo909;QM 986.28
6111228 mmPgiDMALt 1348.95
621992 r7UmSJ\9j 1440.22
310072768 B1ccagCH3 4755.56
819894803 IXfcY9PZG1 4399.39
362945795 5LAdX_s^G 3624.28
99929088 `oHijc^J0u 4507.69
821671 s@OV>NYlacV 4125.72
72368663 Mi?wTcZ_@I 2845.24
22692406 uT05^2plu 2530.73
343817 pB;Glu5sVb7P 2168.28
5138360 877<cT4T;t 1562.15
int[] a = {1,2,3};
doesNothing(a);
for (int i: a)
System.out.print(i);
doesSomething(a);
for (int i: a)
System.out.print(i);
}
static void doesNothing(int[] a) {
a = new int[]{4,5,6};
}
static void doesSomething(int[] a) {
a[0] = 7;
a[1] = 8;
a[2] = 9;
}