accountmanager.java

< ProJavaProgrammingSecondEdition> 书中例程源码

public class AccountManager {

  protected CustomerAccount savings;
  protected CustomerAccount checking;

  public final static int SAVINGS_ACCOUNT = 1;
  public final static int CHECKING_ACCOUNT = 2;

  public static void main(String[] args) {
    int transfers = 1000000;
    try {
      transfers = Integer.parseInt(args[0]);
    } catch (Exception e) {}
    AccountManager am = new AccountManager(transfers);
  }

  public AccountManager(int transfers) {
    savings = new CustomerAccount(SAVINGS_ACCOUNT, 1000);
    checking = new CustomerAccount(CHECKING_ACCOUNT, 1000);
    java.text.NumberFormat formatter =
        java.text.NumberFormat.getCurrencyInstance(
        java.util.Locale.US);
    System.out.println("Total balance before transfers: " +
        formatter.format(savings.getBalance() +
        checking.getBalance()));
    TransferManager tm1 = new TransferManager(checking,
        savings, transfers);
    TransferManager tm2 = new TransferManager(savings,
        checking, transfers);
    //  Create two threads
    Thread t1 = new Thread(tm1);
    Thread t2 = new Thread(tm2);
    //  Initiate execution of the threads
    t1.start();
    t2.start();
    //  Wait for both threads to complete execution
    try {
      t1.join();
      t2.join();
    } catch (Exception e) {};
    System.out.println("Total balance after transfers: " +
        formatter.format(savings.getBalance() +
        checking.getBalance()));
  }

  class TransferManager implements Runnable {

    protected CustomerAccount fromAccount;
    protected CustomerAccount toAccount;
    protected int transferCount;

    public TransferManager(CustomerAccount fromacct,
        CustomerAccount toacct, int transfers) {
      fromAccount = fromacct;
      toAccount = toacct;
      transferCount = transfers;
    }

    public void run() {
    double balance;
    double transferAmount;
    for (int i = 0 ; i < transferCount; i++) {
      balance = fromAccount.getBalance();
      transferAmount = (int)(balance * Math.random());
      transferFunds(fromAccount, toAccount, transferAmount);
    }
    }

  protected void transferFunds(CustomerAccount account1,
      CustomerAccount account2, double transferAmount) {
    double balance;
    CustomerAccount holder = null;
    //  We want to always synchronize first on the account with the
    //  smaller account type value. If it turns out that the "second"
    //  account actually has a larger type value, we'll simply
    //  switch the two references and multiply the amount being
    //  transferred by -1.
    if (account1.getAccountType() > account2.getAccountType()) {
      holder = account1;
      account1 = account2;
      account2 = holder;
      transferAmount *= -1;
    }
    synchronized (account1) {
      synchronized (account2) {
        balance = account1.getBalance();
        balance -= transferAmount;
        account1.setBalance(balance);
        balance = account2.getBalance();
        balance += transferAmount;
        account1.setBalance(balance);
      }
    }
  }

  }

  class CustomerAccount {

    protected int accountType;
    protected double balance;

    public CustomerAccount(int type, double bal) {
      accountType = type;
      balance = bal;
    }

    public int getAccountType() {
      return accountType;
    }

    public double getBalance() {
      return balance;
    }

    public void setBalance(double newbal) {
      balance = newbal;
    }

  }

}