transfer problem

gistfile1.txt

import java.math.BigDecimal;

public final class Transfer {
    private Transfer(){}

    public static void transfer(User from, User to, BigDecimal amount) {

        synchronized (from) {
            if(from.getBalance().compareTo(amount) >= 0) {
                synchronized (to) {
                    from.setBalance(from.getBalance().subtract(amount));
                    to.setBalance(to.getBalance().add(amount));

                }
            }
        }
    }



    public static void main(String[] args) throws Exception {

        User user1 = new User("abc", new BigDecimal("1000000"));
        User user2 = new User("xyz", new BigDecimal("1000000"));


        Object waiter = new Object();
        Thread t1 = new Trans(user1, user2, waiter);
        Thread t2 = new Trans(user2, user1, waiter);
        //Thread t3 = new Trans(user2, user1, waiter);

        t1.start();
        t2.start();
        //t3.start();
        waiter.notifyAll();
        t1.join();
        t2.join();
        //t3.join();

        System.out.println("transfer finished, user1 has "+ user1.getBalance().toPlainString() + ", user2 has " + user2.getBalance().toPlainString());
    }

    static class Trans extends Thread {

        private static final BigDecimal tAmount = new BigDecimal("5");
        final User f;
        final User t;
        final Object w;
        public Trans(User from, User to, Object waiter) {
            f = from;
            t = to;
            w = waiter;
        }

        @Override
        public void run() {
            try {
                w.wait();
            }
            catch (Exception e) {

            }
            for(int i = 0; i < 10000; i++) {
                System.out.println("transfer from " + f.getId() + " to " + t.getId());
                transfer(f, t, tAmount);
            }
        }
    }

    public static class User {

        private String id;
        private BigDecimal balance;

        public User(String id, BigDecimal balance) {
            this.id = id;
            this.balance = balance;
        }

        public String getId() {
            return id;
        }

        public void setId(String id) {
            this.id = id;
        }

        public BigDecimal getBalance() {
            return balance;
        }

        public void setBalance(BigDecimal balance) {
            this.balance = balance;
        }

    }

}