1.生产者和消费者问题Synchronized版

面试：单例模式、排序算法、生产者消费者、死锁

package com.kuang.pc;/*** 线程之间的通信问题，生产者和消费者问题！ 等待唤醒 ，通知唤醒* 线程交替执行 A B 操作同一个变量 num=0* A num+1;* B num-1;*/
public class A {public static void main(String[] args) {Data data = new Data();new Thread(()->{for (int i = 0; i < 10; i++) {try {data.increment();} catch (InterruptedException e) {e.printStackTrace();}}},"A").start();new Thread(()->{for (int i = 0; i < 10; i++) {try {data.decrement();} catch (InterruptedException e) {e.printStackTrace();}}},"B").start();}}
// 判断等待，业务，通知
class Data{//数字  资源类private  int num = 0;//+1public synchronized void increment() throws InterruptedException {if(num!=0){//等待this.wait();}num++;//通知其他线程，我+1完毕了System.out.println(Thread.currentThread().getName()+"=>"+num);this.notifyAll();}//+1public synchronized void decrement() throws InterruptedException {if(num==0){//等待this.wait();}num--;//通知其他线程，我-1完毕了System.out.println(Thread.currentThread().getName()+"=>"+num);this.notifyAll();}}

问题A B C D 开四个线程跑，在if判断之后被唤醒，没判断条件被执行了两次增加，导致的虚假唤醒问题。 

package com.kuang.pc;/*** 线程之间的通信问题，生产者和消费者问题！ 等待唤醒 ，通知唤醒* 线程交替执行 A B 操作同一个变量 num=0* A num+1;* B num-1;*/
public class A {public static void main(String[] args) {Data data = new Data();new Thread(()->{for (int i = 0; i < 10; i++) {try {data.increment();} catch (InterruptedException e) {e.printStackTrace();}}},"A").start();new Thread(()->{for (int i = 0; i < 10; i++) {try {data.decrement();} catch (InterruptedException e) {e.printStackTrace();}}},"B").start();new Thread(()->{for (int i = 0; i < 10; i++) {try {data.increment();} catch (InterruptedException e) {e.printStackTrace();}}},"C").start();new Thread(()->{for (int i = 0; i < 10; i++) {try {data.decrement();} catch (InterruptedException e) {e.printStackTrace();}}},"D").start();}}
// 判断等待，业务，通知
class Data{//数字  资源类private  int num = 0;//+1public synchronized void increment() throws InterruptedException {while (num!=0){//等待this.wait();}num++;//通知其他线程，我+1完毕了System.out.println(Thread.currentThread().getName()+"=>"+num);this.notifyAll();}//+1public synchronized void decrement() throws InterruptedException {while (num==0){//等待this.wait();}num--;//通知其他线程，我-1完毕了System.out.println(Thread.currentThread().getName()+"=>"+num);this.notifyAll();}}

 

2.新版Lock锁解决消费者生产者问题。 

 

package com.kuang.pc;import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;/*** 线程之间的通信问题，生产者和消费者问题！ 等待唤醒 ，通知唤醒* 线程交替执行 A B 操作同一个变量 num=0* A num+1;* B num-1;*/
public class B {public static void main(String[] args) {Data1 data = new Data1();new Thread(()->{for (int i = 0; i < 10; i++) {try {data.increment();} catch (InterruptedException e) {e.printStackTrace();}}},"A").start();new Thread(()->{for (int i = 0; i < 10; i++) {try {data.decrement();} catch (InterruptedException e) {e.printStackTrace();}}},"B").start();new Thread(()->{for (int i = 0; i < 10; i++) {try {data.increment();} catch (InterruptedException e) {e.printStackTrace();}}},"C").start();new Thread(()->{for (int i = 0; i < 10; i++) {try {data.decrement();} catch (InterruptedException e) {e.printStackTrace();}}},"D").start();}}// 判断等待，业务，通知
class Data1 {//数字  资源类private int num = 0;Lock lock=new ReentrantLock();Condition condition = lock.newCondition();
//        condition.await();等待
//        condition.signalAll();唤醒全部//+1public void increment() throws InterruptedException {lock.lock();try {//业务代码while (num != 0) {//等待condition.await();}num++;System.out.println(Thread.currentThread().getName() + "=>" + num);//通知其他线程，我+1完毕了condition.signalAll();} catch (Exception e) {e.printStackTrace();} finally {lock.unlock();}}//+1public void decrement() throws InterruptedException {lock.lock();try {//业务代码while (num == 0) {//等待condition.await();}num--;System.out.println(Thread.currentThread().getName() + "=>" + num);//通知其他线程，我-1完毕了condition.signalAll();} catch (Exception e) {e.printStackTrace();} finally {lock.unlock();}}}

任何一个新的技术，绝对不是仅仅只覆盖了原来的技术，优势，和补充！

Condition 优势精准通知，唤醒线程

package com.kuang.pc;import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;/*** 线程之间的通信问题，生产者和消费者问题！ 等待唤醒 ，通知唤醒* 线程交替执行 A B 操作同一个变量 num=0* A num+1;* B num-1;*/
public class C {public static void main(String[] args) {Data2 data = new Data2();new Thread(()->{for (int i = 0; i < 10; i++) {data.printA();}},"A").start();new Thread(()->{for (int i = 0; i < 10; i++) {data.printB();}},"B").start();new Thread(()->{for (int i = 0; i < 10; i++) {data.printC();}},"C").start();}}
// 判断等待，业务，通知
class Data2 {//数字  资源类private Lock lock=new ReentrantLock();private Condition condition1 = lock.newCondition();private Condition condition2 = lock.newCondition();private Condition condition3 = lock.newCondition();private int num=1;public void printA(){lock.lock();try {if (num!=1){//等待condition1.await();}num=2;System.out.println(Thread.currentThread().getName()+":Aaa");//唤醒，唤醒指定的人，Bcondition2.signal();} catch (Exception e) {e.printStackTrace();} finally {lock.unlock();}}public void printB(){lock.lock();try {if (num!=2){condition2.await();}num=3;System.out.println(Thread.currentThread().getName()+":Bbb");condition3.signal();} catch (Exception e) {e.printStackTrace();} finally {lock.unlock();}}public void printC(){lock.lock();try {if (num!=3){condition3.await();}System.out.println(Thread.currentThread().getName()+":Ccc");num=1;condition1.signal();} catch (Exception e) {e.printStackTrace();} finally {lock.unlock();}}}

精准唤醒线程  Condition