1  // Purpose.  wait() and notifyAll() demo
   
 2  class Account {
 3     private int balance = 0;
   
 4     public synchronized void deposit( int a ) {
 5        balance += a;
 6        System.out.println( "balance increased by " + a );
 7        notifyAll();
 8     }
 9     public synchronized void withdraw( int a ) {
10        while (balance < a) {
11           System.out.println( "withdraw " + a + " waiting" );
12           try { wait(); } catch(InterruptedException e) { }
13        }
14        balance -= a;
15        System.out.println( "balance decreased by " + a );
16  }  }
   
17  class AccountUpdate extends Thread {
18     private Account acct;
19     private int     amt;
   
20     public AccountUpdate( Account a, int i ) {
21        acct = a;  amt  = i;
22     }
23     public void run() {
24        if (amt > 0) acct.deposit( amt );
25        else         acct.withdraw( -amt );
26  }  }
   
27  public class ThreadWithdraw {
28     public static void main( String argv[] ) {
29        Account acct = new Account();
30        new AccountUpdate( acct, -20 ).start();
31        new AccountUpdate( acct,  10 ).start();
32        try { Thread.sleep(100); } catch (Exception e) { }
33        new AccountUpdate( acct, -40 ).start();
34        new AccountUpdate( acct,  20 ).start();
35        try { Thread.sleep(100); } catch (Exception e) { }
36        new AccountUpdate( acct,  30 ).start();
37  }  }
   
38  // withdraw 20 waiting
39  // balance increased by 10
40  // withdraw 20 waiting
41  // withdraw 40 waiting
42  // balance increased by 20
43  // balance decreased by 20
44  // withdraw 40 waiting
45  // balance increased by 30
46  // balance decreased by 40