多线程start有关问题

package net.xinxin.test;public class BankAccount {    private int number;        private int balance;        public BankAccount(int number,int balance)    {        this.number=number;        this.balance=balance;    }    public int getBalance()    {        return balance;    }        public void deposit(int amount)    {        balance = balance + amount;    }        public void withdraw(int amount)    {        balance = balance-amount;    }        public static void main(String[] args)throws Exception    {        BankAccount a = new BankAccount(1, 1000);        Thread t1 = new Thread(new Depositor(a, 100),"depositor");            t1.start();        //t1.join();        System.out.println(a.getBalance());    }        static class Depositor implements Runnable    {        BankAccount account;        int amount;        public Depositor(BankAccount account,int amount)        {            this.account=account;            this.amount=amount;        }        public void run(){                        for(int i=0;i<10000;i++)            {                account.deposit(amount);                //System.out.println(account.getBalance()); //不加此句运行结果1000 加上之后结果正常            }        }    }        static class Withdrawer implements Runnable    {        BankAccount account;        int amount;        public Withdrawer(BankAccount account,int amount) {            this.account=account;            this.amount=amount;        }        public void run()        {            for(int i=0;i<10000;i++)                account.withdraw(amount);        }    }    }