线程锁

public class test {
    public static void main(String[] args) throws Throwable {
        C c = new C();
        Thread t = new Thread(()->c.a());
        t.start();
        Thread t2 = new Thread(()->c.b());
        t2.start();
        Thread t3 = new Thread(()->c.c());
        t3.start();
    }
}
class C{
    synchronized void a() {
        System.out.println(1);
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(2);
    }
    synchronized void b() {
        System.out.println(3);
    }
    void c() {
        System.out.println(4);
    }
}