Java多线程实战之交叉打印的两种方法

public class MyService {
 private volatile boolean flag = false;
 public synchronized void printA() {
 try {
  while (flag) {
  wait();
  }
  for (int i = 0; i < 5; i++) {
  System.out.println("printA...");
  TimeUnit.SECONDS.sleep(1);
  }
  flag = true;
  notifyAll();
 } catch (InterruptedException e) {
  e.printStackTrace();
 }
 }
 public synchronized void printB() {
 try {
  while (!flag) {
  wait();
  }
  for (int i = 0; i < 5; i++) {
  System.out.println("printB...");
  TimeUnit.SECONDS.sleep(1);
  }
  flag = false;
  notifyAll();
 } catch (InterruptedException e) {
  e.printStackTrace();
 }
 }
}

public class BackupA implements Runnable {
 private MyService myService;
 public BackupA(MyService myService) {
 super();
 this.myService = myService;
 }
 @Override
 public void run() {
 myService.printA();
 }
}

public class BackupB implements Runnable {
 private MyService myService;
 public BackupB(MyService myService) {
 super();
 this.myService = myService;
 }
 @Override
 public void run() {
 myService.printB();
 }
}

public class Run {
 public static void main(String[] args) {
 MyService myService = new MyService();
 for (int i = 0; i < 20; i++) {
  new Thread(new BackupA(myService)).start();
  new Thread(new BackupB(myService)).start();
 }
 }
}

public class MyService {
 private Lock lock = new ReentrantLock();
 private Condition condition = lock.newCondition();
 private boolean flag = false;
 public void printA() {
 try {
  lock.lock();
  while (flag) {
  condition.await();
  }
  for (int i = 0; i < 5; i++) {
  System.out.println("printA...");
  TimeUnit.SECONDS.sleep(1);
  }
  flag = true;
  condition.signalAll();
 } catch (InterruptedException e) {
  e.printStackTrace();
 } finally {
  lock.unlock();
 }
 }
 public void printB() {
 try {
  lock.lock();
  while (!flag) {
  condition.await();
  }
  for (int i = 0; i < 5; i++) {
  System.out.println("printB...");
  TimeUnit.SECONDS.sleep(1);
  }
  flag = false;
  condition.signalAll();
 } catch (InterruptedException e) {
  e.printStackTrace();
 } finally {
  lock.unlock();
 }
 }
}

public class ThreadA implements Runnable {
 private MyService myService;
 public ThreadA(MyService myService) {
 super();
 this.myService = myService;
 }
 @Override
 public void run() {
 myService.printA();
 }
}

public class ThreadB implements Runnable {
 private MyService myService;
 public ThreadB(MyService myService) {
 super();
 this.myService = myService;
 }
 @Override
 public void run() {
 myService.printB();
 }
}

public class Run {
 public static void main(String[] args) {
 MyService myService = new MyService();
 for (int i = 0; i < 20; i++) {
  new Thread(new ThreadA(myService)).start();
  new Thread(new ThreadB(myService)).start();
 }
 }
}