쓰레드 critical section, Java

Language: Layout:

//'main' method must be in a class 'Rextester'.
//Compiler version 1.8.0_72

class Rextester {
	public static void main(String[] args) {
		SharedArea area = new SharedArea();
		area.account1 = new Account("111-111-111","이몽룡",20000000);
		area.account2 = new Account("222-222-222","성춘향",10000000);
		TransferThread thread1 = new TransferThread(area);
		PrintThread thread2 = new PrintThread(area);
		thread1.start();
		thread2.start();
	}
}

class TransferThread extends Thread
{
	SharedArea sharedArea;
	TransferThread(SharedArea area)
	{
		sharedArea=area;
	}
	public void run()
	{
		for(int cnt=0;cnt<12;cnt++)
		{
			synchronized (sharedArea) {
			sharedArea.account1.withdraw(1000000);
			System.out.println("이몽룡 계좌 : 100만원 인출");
			sharedArea.account2.deposit(1000000);
			System.out.println("성춘향 계좌 : 100만원 입금");
			}
		}
	}
}

class Account
{
	String AccountNo;
	String ownerName;
	int balance;
	
	Account(String accountNo, String ownerName, int balance)
	{
		this.AccountNo=accountNo;
		this.ownerName=ownerName;
		this.balance=balance;
	}
	void deposit(int amount)
	{
		balance += amount;
	}
	int withdraw(int amount)
	{
		if(balance < amount)
			return 0;
		balance -= amount;
		return amount;
	}
}

class SharedArea
{
	Account account1;
	Account account2;
}

class PrintThread extends Thread
{
	SharedArea sharedArea;
	PrintThread(SharedArea area)
	{
		sharedArea = area;
	}
	public void run()
	{
		for(int cnt=0;cnt<3;cnt++)
		{
			synchronized (sharedArea) {
			int sum=sharedArea.account1.balance + sharedArea.account2.balance;
			System.out.println("계좌 잔액 합계 : " + sum);
			}
		try
		{
			Thread.sleep(1);
		}
		catch(InterruptedException e)
		{
			System.out.println(e.getMessage());
		}
	}
}
}

[ + ] Show input
Compilation time: 0.52 sec, absolute running time: 0.14 sec, cpu time: 0.07 sec, memory peak: 19 Mb, absolute service time: 0,66 sec