编写一个程序，开启三个线程， 这三个线程的 ID 分别是 A、B 和 C ， 每个线程把自己的 ID 在屏幕上打印 10 遍， 要求输出结果必须按 ABC 的顺序显示，如 ABCABCABC… 依次递推
最近同事面试阿里某部门，被问到了这个题，遥想18年的时候就被问过，记录一下。
信号量版本
import java.util.concurrent.Semaphore;
public class Test {
static class CustomerRunnable implements Runnable {
String name;
Semaphore waitSemaphore;
Semaphore nextSemaphore;
public CustomerRunnable(String name, Semaphore waitSemaphore, Semaphore nextSemaphore) {
this.name = name;
this.waitSemaphore = waitSemaphore;
this.nextSemaphore = nextSemaphore;
}
public void run() {
for (int i = 0; i < 10; i++) {
try {
waitSemaphore.acquire();
System.out.println(name);
nextSemaphore.release();
} catch (InterruptedException e) {
}
}
}
}
public static void main(String[] args) {
Semaphore A = new Semaphore(0), B = new Semaphore(0), C = new Semaphore(0);
Thread threadA = new Thread(new CustomerRunnable("A", A, B));
Thread threadB = new Thread(new CustomerRunnable("B", B, C));
Thread threadC = new Thread(new CustomerRunnable("C", C, A));
threadA.start();
threadB.start();
threadC.start();
A.release();
}
}
volatile版本
同事的方案
public class Test {
static class CustomerRunnable implements Runnable {
private static volatile int flag;
int remain;
String name;
public CustomerRunnable(String name, Integer remain) {
this.name = name;
this.remain = remain;
}
public void run() {
for (int i = 0; i < 10; ) {
if (flag % 3 == remain) {
i++;
System.out.println(name);
flag++;
}
}
}
}
public static void main(String[] args) {
Thread threadA = new Thread(new CustomerRunnable("A", 0));
Thread threadB = new Thread(new CustomerRunnable("B", 1));
Thread threadC = new Thread(new CustomerRunnable("C", 2));
threadA.start();
threadB.start();
threadC.start();
}
}
