Multi-threaded learning (1) bank deposit and withdrawal

Today, my classmates asked about bank deposits and withdrawals, how to keep synchronization, and wrote a simple example.

First is the bank:

private int money = 1000;
    
    public synchronized void add(int n) {
        money += n;
        try {
            Thread.sleep(1000);
        } catch (Exception e) {
            e.printStackTrace();
        }
        System.out.println(Thread.currentThread().getName() + "----余额: " + money);
    }
    
    public synchronized void reduce(int n) {
        if(money - n >= 0) {
            money -= n;
        } else {
            System.out.println("余额不足");
        }
        try {
            Thread.sleep(1000);
        } catch (Exception e) {
            e.printStackTrace();
        }
        System.out.println(Thread.currentThread().getName() + "----余额: " + money);
    }

The key is method locking, which uses the built-in mutex lock mechanism of java.

Next is the user:

    public Bank bank;
    static final String TYPE_ADD = "add";  
    static final String TYPE_REDUCE = "reduce";
    private String type;  
    private int time;
    private int money;  
    public Customer() {  
    }  
 
    public Customer(Bank bank, String type, int time, int money) {  
        this.bank = bank;  
        this.type = type;  
        this.time = time;  
        this.money = money;  
    }
    
    @Override
    public void run() {
        for(int i = 0; i < time; i++) {
            if (TYPE_ADD.equals(type)) {  
                bank.add(money);  
            } else if (TYPE_REDUCE.equals(type)) {  
                bank.reduce(money);  
            }
        }
    }

And finally the test class:

    Bank bank = new Bank();
        Customer a1 = new Customer(bank, Customer.TYPE_ADD, 10, 100);
        Customer a2 = new Customer(bank, Customer.TYPE_REDUCE, 10, 100);
        
        Thread t1 = new Thread(a1);
        Thread t2 = new Thread(a2);
        t1.start();
        t2.start();