Java并发面试题：三个线程轮流打印十次abc

方法1：用while循环和变量实现

static int index = 1;

public static void main(String[] args) {
Thread t1 = new Thread(new Runnable() {
@Override
public void run() {
while (true) {
if (index > 30) {
break;
}
if (index % 3 == 1) {
System.out.println("a");
index++;
}
}
}
});
Thread t2 = new Thread(new Runnable() {
@Override
public void run() {
while (true) {
if (index > 30) {
break;
}
if (index % 3 == 2) {
System.out.println("b");
index++;
}
}
}
});
Thread t3 = new Thread(new Runnable() {
@Override
public void run() {
while (true) {
if (index > 30) {
break;
}
if (index % 3 == 0) {
System.out.println("c");
index++;
}
}
}
});
t1.start();
t2.start();
t3.start();
}

方法2：用synchronized、wait、notifyAll实现

static int index = 1;

public static void main(String[] args) throws InterruptedException {
final Object lock = new Object();
Thread t1 = new Thread(new Runnable() {
@Override
public void run() {
synchronized (lock) {
for (int i = 0; i < 10; i++) {
while (index % 3 != 1) {
try {
lock.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
System.out.println("a");
index++;
lock.notifyAll();
}
}
}
});
Thread t2 = new Thread(new Runnable() {
@Override
public void run() {
synchronized (lock) {
for (int i = 0; i < 10; i++) {
while (index % 3 != 2) {
try {
lock.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
System.out.println("b");
index++;
lock.notifyAll();
}
}
}
});
Thread t3 = new Thread(new Runnable() {
@Override
public void run() {
synchronized (lock) {
for (int i = 0; i < 10; i++) {
while (index % 3 != 0) {
try {
lock.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
System.out.println("c");
index++;
lock.notifyAll();
}
}
}
});
t1.start();
t2.start();
t3.start();
}

方法3：用ReentrantLock、1个Condition实现

static int index = 1;

public static void main(String[] args) {
final ReentrantLock lock = new ReentrantLock();
final Condition condition = lock.newCondition();
Thread t1 = new Thread(new Runnable() {
@Override
public void run() {
lock.lock();
try {
for (int i = 0; i < 10; i++) {
while (index % 3 != 1) {
condition.await();
}
System.out.println("a");
index++;
condition.signalAll();
}
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
});
Thread t2 = new Thread(new Runnable() {
@Override
public void run() {
lock.lock();
try {
for (int i = 0; i < 10; i++) {
while (index % 3 != 2) {
condition.await();
}
System.out.println("b");
index++;
condition.signalAll();
}
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
});
Thread t3 = new Thread(new Runnable() {
@Override
public void run() {
lock.lock();
try {
for (int i = 0; i < 10; i++) {
while (index % 3 != 0) {
condition.await();
}
System.out.println("c");
index++;
condition.signalAll();
}
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
});
t1.start();
t2.start();
t3.start();
}

方法4：用ReentrantLock、三个Condition实现

public static void main(String[] args) {
final Lock lock = new ReentrantLock();
final Condition condition1 = lock.newCondition();
final Condition condition2 = lock.newCondition();
final Condition condition3 = lock.newCondition();
Thread t1 = new Thread(new Runnable() {
@Override
public void run() {
lock.lock();
try {
for (int i = 0; i < 10; i++) {
condition1.await();
System.out.println("a");
condition2.signal();
}
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
});
Thread t2 = new Thread(new Runnable() {
@Override
public void run() {
lock.lock();
try {
for (int i = 0; i < 10; i++) {
condition2.await();
System.out.println("b");
condition3.signal();
}
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
});
Thread t3 = new Thread(new Runnable() {
@Override
public void run() {
lock.lock();
try {
for (int i = 0; i < 10; i++) {
condition3.await();
System.out.println("c");
condition1.signal();
}
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
});
t1.start();
t2.start();
t3.start();
try {
Thread.sleep(1000);
lock.lock();
condition1.signal();
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}

方法5：用Semaphore实现

public static void main(String[] args) {
final Semaphore semaphore1 = new Semaphore(1);
final Semaphore semaphore2 = new Semaphore(0);
final Semaphore semaphore3 = new Semaphore(0);
Thread t1 = new Thread(new Runnable() {
@Override
public void run() {
for (int i = 0; i < 10; i++) {
try {
semaphore1.acquire();
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("a");
semaphore2.release();
}
}
});
Thread t2 = new Thread(new Runnable() {
@Override
public void run() {
for (int i = 0; i < 10; i++) {
try {
semaphore2.acquire();
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("b");
semaphore3.release();
}
}
});
Thread t3 = new Thread(new Runnable() {
@Override
public void run() {
for (int i = 0; i < 10; i++) {
try {
semaphore3.acquire();
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("c");
semaphore1.release();
}
}
});
t1.start();
t2.start();
t3.start();
}