6. 동기화

public interface BankAccount {

    boolean withdraw(int amount);

    int getBalance();
}

public class MyBankAccount implements BankAccount {

    private int balance;

    public MyBankAccount(int initialBalance) {
        this.balance = initialBalance;
    }

    @Override
    public synchronized boolean withdraw(int amount) {
        log("거래 시작: " + getClass().getSimpleName());

        log("[검증 시작] 출금액: " + amount + ", 잔액: " + balance);
        if (balance < amount) {
            log("[검증 실패] 출금액: " + amount + ", 잔액: " + balance);
            return false;
        }
        log("[검증 완료] 출금액: " + amount + ", 잔액: " + balance);
        sleep(1000);
        balance = balance - amount;
        log("[출금 완료] 출금액: " + amount + ", 변경 잔액: " + balance);

        log("거래 종료");
        return true;
    }

    @Override
    public synchronized int getBalance() {
        return balance;
    }
}

public class WithdrawTask implements Runnable {

    private BankAccount account;
    private int amount;

    public WithdrawTask(BankAccount account, int amount) {
        this.account = account;
        this.amount = amount;
    }

    @Override
    public void run() {
        account.withdraw(amount);
    }
}

public class BankMain {

    public static void main(String[] args) throws InterruptedException {
        BankAccount account = new MyBankAccount(1000);

        Thread t1 = new Thread(new WithdrawTask(account, 800), "t1");
        Thread t2 = new Thread(new WithdrawTask(account, 800), "t2");

        t1.start();
        t2.start();

        sleep(500);
        log("t1 state: " + t1.getState());
        log("t2 state: " + t2.getState());

        t1.join();
        t2.join();
        log("최종 잔액: " + account.getBalance());
    }
}