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我一直在2.4上工作，並且遇到程序無法正常工作，出現空指針異常，因爲它無法獲取源和目標的帳號。現在我用50個事務運行程序，但是我使用更多的空指針異常出現，如果你能指導我到正確的路徑，那將是非常好的。該代碼發佈如下。BankAccount問題和線程，請幫忙
以下是輸出示例。
Withdrawing 592.5 from account 3
Balance is: 9339.92
Balance is: 9339.92
Withdrawing 496.81 from account 7
Withdrawing 233.86 from account 2
Balance is: 9339.92
Withdrawing 366.35 from account 5
Depositing 366.35 from account 6
Transfer occuring from 5 to 6 done.
Depositing 32.8 from account 6
Depositing 911.01 from account 8
Transfer occuring from 1 to 8
Withdrawing 601.23 from account 1
Depositing 601.23 from account 8
Transfer occuring from 1 to 8 done.
Withdrawing 115.42 from account 8
Transfer occuring from 8 to 5
Withdrawing 886.08 from account 8
Depositing 886.08 from account 5
Transfer occuring from 8 to 5 done.
Transfer occuring from 8 to 9
Withdrawing 820.83 from account 8
Transfer occuring from 5 to 7
Withdrawing 50.96 from account 5
Depositing 50.96 from account 7
Transfer occuring from 5 to 7 done.
Balance is: 8738.69
Exception in thread "Thread-43" Depositing 820.83 from account 9
Transfer occuring from 8 to 9 done.
[b]java.lang.NullPointerException
at OrderedTeller.transfer(OrderedTeller.java:54)
at OrderedTeller.run(OrderedTeller.java:29)[/b]
Withdrawing 361.35 from account 2
Depositing 472.04 from account 9
Balance is: 9452.789999999999
Transfer occuring from 1 to 2
Withdrawing 255.33 from account 1
Depositing 255.33 from account 2
Transfer occuring from 1 to 2 done.
Depositing 359.63 from account 2
Depositing 880.57 from account 6
Depositing 734.09 from account 7
Withdrawing 210.11 from account 4
Depositing 640.98 from account 5
Withdrawing 172.63 from account 5
代碼：
public class Bank {
private List<BankAccount> bankAccounts = new ArrayList<BankAccount>();
public Bank() {
for (int i = 0; i < 10; i++) {
bankAccounts.add(new BankAccount(i, 10000.00));
}
doTransActions("Transactions.txt");
}
public void doTransActions(String fileName) {
BufferedReader in = null;
try {
String strLine = null;
in = new BufferedReader(new FileReader(fileName));
int distinationAccount = 0;
int sourceAccount = 0;
double amount = 0;
while ((strLine = in.readLine()) != null) {
java.lang.String[] tokens = strLine.split("[%]");
String transaction = tokens[0];
if (transaction.equals("TRANSFER")) {
sourceAccount = Integer.parseInt(tokens[1]);
distinationAccount = Integer.parseInt(tokens[2]);
amount = Double.parseDouble(tokens[3]);
BankAccount source = null;
BankAccount distination = null;
for (BankAccount account : bankAccounts) {
if (account.getNumber() == sourceAccount) {
source = account;
}
if (account.getNumber() == distinationAccount) {
distination = account;
}
}
new OrderedTeller(source, distination, transaction, amount).start();
} else {
sourceAccount = Integer.parseInt(tokens[1]);
amount = Double.parseDouble(tokens[2]);
BankAccount source = null;
for (BankAccount account : bankAccounts) {
if (account.getNumber() == sourceAccount) {
source = account;
}
}
new OrderedTeller(source, transaction, amount).start();
}
}
} catch (IOException e) {
System.out.println(e.getMessage());
} finally {
try {
in.close();
} catch (IOException e) {
System.out.println(e.getMessage());
}
}
}
}
public class OrderedTeller extends Thread {
private BankAccount source = null, dest = null;
private String transType = null;
private double amount = 0;
public OrderedTeller(BankAccount a, BankAccount b, String transType, double amount)
{
source = a;
dest = b;
this.amount = amount;
this.transType = transType;
}
public OrderedTeller(BankAccount a, String transType, double amount)
{
source = a;
this.amount = amount;
this.transType = transType;
}
public void run() {
if (transType.equals("TRANSFER")) {
transfer(amount);
} else if (transType.equals("WITHDRAW")) {
source.withdraw(amount);
} else if (transType.equals("DEPOSIT")) {
source.deposit(amount);
} else if (transType.equals("BALANCE")) {
System.out.println("Balance is: "+source.getBalance());
} else {
System.out.println("ERROR: TRANSACTION TYPE NOT RECOGNIZED");
}
}
public void transfer(double amount) {
BankAccount first, second;
if (source.getNumber() < dest.getNumber()) {
first = source;
second = dest;
} else {
first = dest;
second = source;
}
synchronized (first) {
Thread.yield();
synchronized (second) {
System.out.println("Transfer occuring from " + source.getNumber() + " to " + dest.getNumber());
source.withdraw(amount);
dest.deposit(amount);
System.out.println("Transfer occuring from " + source.getNumber() + " to " + dest.getNumber()+ " done.");
}
}
}
}
public class BankAccount {
private double balance = 0;
private int number = 0;
public BankAccount(int number, double initialBalance) {
this.number = number;
balance = initialBalance;
}
public int getNumber() {
return number;
}
public double getBalance() {
return balance;
}
public synchronized void deposit(double amount) {
double prevBalance = balance;
System.out.println("Depositing " + amount + " from account " + number);
balance = prevBalance + amount;
}
public synchronized void withdraw(double amount) {
double prevBalance = balance;
System.out.println("Withdrawing " + amount + " from account " + number);
balance = prevBalance - amount;
}
}
這是文本文件，我從 閱讀交易的每一行與真實文本文件中的交易開始。
TRANSFER%4%3%866.85
TRANSFER%2%7%861.79
BALANCE%9%895.41
DEPOSIT%7%475.82
WITHDRAW%3%845.92
WITHDRAW%4%766.69
BALANCE%10%591.67
DEPOSIT%8%12.22
TRANSFER%3%6%57.45
BALANCE%10%417.84
TRANSFER%10%8%928.33
TRANSFER%9%7%94.46
WITHDRAW%5%874.17
DEPOSIT%9%538.37
BALANCE%9%324.88
TRANSFER%6%7%773.23
DEPOSIT%3%81.81
BALANCE%8%564.51
TRANSFER%6%2%300.17
TRANSFER%5%6%366.35
DEPOSIT%10%627.87
DEPOSIT%8%911.01
TRANSFER%1%2%535.72
TRANSFER%1%8%601.23
TRANSFER%1%6%124.36
WITHDRAW%8%115.42
BALANCE%3%942.87
TRANSFER%8%5%886.08
DEPOSIT%7%604.41
WITHDRAW%2%361.35
WITHDRAW%2%233.86
WITHDRAW%4%210.11
DEPOSIT%6%32.8
DEPOSIT%6%880.57
WITHDRAW%7%496.81
WITHDRAW%5%172.63
BALANCE%1%70.4
DEPOSIT%7%734.09
BALANCE%1%274.6
DEPOSIT%5%640.98
WITHDRAW%3%592.5
DEPOSIT%9%472.04
BALANCE%1%647.71
TRANSFER%3%10%537.52
BALANCE%1%461.09
BALANCE%3%172.58
TRANSFER%8%9%820.83
TRANSFER%1%2%255.33
TRANSFER%5%7%50.96
DEPOSIT%2%359.63
我已經（至少部分）格式化了代碼（和文本），但是我必須說我有點懷疑它會做很多好事。在大多數人非常努力地幫助診斷你的問題之前，你真的需要將問題縮小到更合理大小的代碼塊。 – 2011-02-16 07:02:33