我们提供了一个类：
public class Foo {
public void first() { print("first"); }
public void second() { print("second"); }
public void third() { print("third"); }
}?
三个不同的线程 A、B、C 将会共用一个 Foo 实例。
输入: [1,2,3]输出: "firstsecondthird"解释: 有三个线程会被异步启动。输入 [1,2,3] 表示线程 A 将会调用 first() 方法，线程 B 将会调用 second() 方法，线程 C 将会调用 third() 方法。正确的输出是 "firstsecondthird"。输入: [1,3,2]输出: "firstsecondthird"解释: 输入 [1,3,2] 表示线程 A 将会调用 first() 方法，线程 B 将会调用 third() 方法，线程 C 将会调用 second() 方法。正确的输出是 "firstsecondthird"。尽管输入中的数字似乎暗示了顺序，但是我们并不保证线程在操作系统中的调度顺序。
你看到的输入格式主要是为了确保测试的全面性。
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
class Foo {
final Lock lock = new ReentrantLock();
final Condition condition = lock.newCondition();
boolean one , two ;
public Foo() {
}
public void first(Runnable printFirst) throws InterruptedException {
// printFirst.run() outputs "first". Do not change or remove this line.
lock.lock();
try{
printFirst.run();
one = true;
condition.signal();
}finally {
lock.unlock();;
}
}
public void second(Runnable printSecond) throws InterruptedException {
// printSecond.run() outputs "second". Do not change or remove this line.
lock.lock();
try{
while (!one){
condition.await();
}
printSecond.run();
condition.signal();
two = true;
}finally {
lock.unlock();
}
}
public void third(Runnable printThird) throws InterruptedException {
// printThird.run() outputs "third". Do not change or remove this line.
lock.lock();
try{
while (!(one && two)){
condition.await();
}
printThird.run();
}finally {
lock.unlock();
}
}
}class Foo {
AtomicInteger at = new AtomicInteger(0);
public Foo() {
}
public void first(Runnable printFirst) throws InterruptedException {
// printFirst.run() outputs "first". Do not change or remove this line.
printFirst.run();
at.incrementAndGet();
}
public void second(Runnable printSecond) throws InterruptedException {
// printSecond.run() outputs "second". Do not change or remove this line.
while (at.get() != 1) {
}
printSecond.run();
at.incrementAndGet();
}
public void third(Runnable printThird) throws InterruptedException {
// printThird.run() outputs "third". Do not change or remove this line.
while (at.get() != 2) {
}
printThird.run();
}
}来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/print-in-order
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