分析：

1）賬戶的錢必須設定是靜態的

2）所有人操作的是同一個賬戶，操作的時候要加同步鎖

程式碼：

package ThreadTest;
 
import java.util.Objects;
 
public class Bank {
	// 假設一個賬戶有1000塊錢  
	static double money = 1000;
	// 櫃檯Counter取錢的方法  
	private void Counter(double money) {
		Bank.money -= money;
		System.out.println("櫃檯取錢" + money + "元，還剩" + Bank.money + "元！");
	}
	// ATM取錢的方法  
	private void ATM(double money) {
		Bank.money -= money;
		System.out.println("ATM取錢" + money + "元，還剩" + Bank.money + "元！");
	}
	
	//提供一個對外取款途徑，防止直接調取方法同時取款時，併發餘額顯示錯誤
	public synchronized void outMoney(double money, String mode) throws Exception{
		if(money > Bank.money){
			//校驗餘額是否充足
			throw new Exception("取款金額"+money+",餘額只剩"+Bank.money+"，取款失敗");
		}
		if(Objects.equals(mode, "ATM")){
			ATM(money);
		} else {
			Counter(money);
		}
	}
 
}
 

package ThreadTest;
 
public class PersonA extends Thread {
 
	Bank bank;
	
	String mode;
 
	public PersonA(Bank bank, String mode) {
		this.mode = mode;
		this.bank = bank;
	}
 
	public void run (){
		while(bank.money >= 100){
			try {
				bank.outMoney(100, mode);
			} catch (Exception e1) {
				// TODO Auto-generated catch block
				e1.printStackTrace();
			}
			try {
				sleep(100);
			} catch (InterruptedException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
	}
}
 

package ThreadTest;
 
public class PersonB extends Thread {
	Bank bank;
	
	String mode;
 
	public PersonB(Bank bank, String mode) {
		this.bank = bank;
		this.mode = mode;
	}
 
	public void run() {
		while (bank.money >= 200) {
			try {
				bank.outMoney(200, mode);
			} catch (Exception e1) {
				// TODO Auto-generated catch block
				e1.printStackTrace();
			}
			try {
				sleep(100);
			} catch (InterruptedException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
		
	}
}
 

package ThreadTest;
 
/**
 * 兩個人AB通過一個賬戶A在櫃檯取錢和B在ATM機取錢
 * */
public class MainClass {
	public static void main(String[] args) {
		Bank bank = new Bank();
		// 例項化兩個人，傳入同一個銀行的物件
		PersonA a = new PersonA(bank, "Counter");
		PersonB b = new PersonB(bank, "ATM");
		a.start();
		b.start();
	}
}

結果：

櫃檯取錢100.0元，還剩900.0元！
ATM取錢200.0元，還剩700.0元！
ATM取錢200.0元，還剩500.0元！
櫃檯取錢100.0元，還剩400.0元！
櫃檯取錢100.0元，還剩300.0元！
ATM取錢200.0元，還剩100.0元！
櫃檯取錢100.0元，還剩0.0元！