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Java實(shí)現(xiàn)多線程輪流打印1-100的數(shù)字操作

更新時(shí)間：2020年08月26日 11:28:59 作者：一只菜鳥(niǎo).....

這篇文章主要介紹了Java實(shí)現(xiàn)多線程輪流打印1-100的數(shù)字操作，具有很好的參考價(jià)值，希望對(duì)大家有所幫助。一起跟隨小編過(guò)來(lái)看看吧

首先打印1-100數(shù)字如果用一個(gè)單線程實(shí)現(xiàn)那么只要一個(gè)for循環(huán)即可，那么如果要用兩個(gè)線程打印出來(lái)呢？（一個(gè)線程打印奇數(shù)，一個(gè)線程打印偶數(shù)）于是大家會(huì)想到可以通過(guò)加鎖實(shí)現(xiàn)，但是這樣的效率是不是不高？這里我用一個(gè)變量來(lái)控制兩個(gè)線程的輸出

public class ThreadTest {
 volatile int flag=0;
 public void runThread() throws InterruptedException{
   Thread t1=new Thread(new Thread1());
   Thread t2=new Thread(new Thread2());
   t1.start();
   t2.start();
 }
 public class Thread1 implements Runnable{
 
 public void run() {
  int i=0;
  while(i<=99){
  if(flag==0)
  {
   System.out.println("t1="+i+"flag="+flag);
   i+=2;
   flag=1;
  }
  }
 } 
 }
 
 public class Thread2 implements Runnable{
 
 public void run() {
  int i=1;
  while(i<=99){
  if(flag==1)
  {
   System.out.println("t2="+i+"flag="+flag);
   i+=2;
   flag=0;
  }
  }
 }
 
 }
}

那么如果要實(shí)現(xiàn)三個(gè)線程輪流打印1-100的數(shù)字呢？是不是也可以用上面的方法實(shí)現(xiàn)呢？代碼如下

public class ThreadTest {
 private int i=0;
 private Thread thread1,thread2,thread3;
 private int flag=0;
 public void runThread() throws InterruptedException{
   thread1=new Thread(new Thread1());
   thread2=new Thread(new Thread2());
   thread3=new Thread(new Thread3());
   thread1.start();
   thread2.start();
   thread3.start();
 }
 public class Thread1 implements Runnable{
 
 public void run() {
  
  while(i<=100){
  if(flag==0) {
   System.out.println("t1="+i);
   i++;
   flag=1;
  }
  }
 } 
 }
 
 public class Thread2 implements Runnable{
 
 public void run() {
  
  while(i<=100){
  if(flag==1) {
   System.out.println("t2="+i);
   i++;
   flag=2;
  }
  }
 } 
 }
 
 public class Thread3 implements Runnable{
 
 public void run() {
  
  while(i<=100){
  if(flag==2) {
   System.out.println("t3="+i);
   i++;
   flag=0;
  }
  }
 }
 
 }
}

運(yùn)行結(jié)果

發(fā)現(xiàn)三個(gè)線程只打印了一次就停止不輸出了，是什么原因呢？

可以用jdk自帶的jstack來(lái)看看線程的狀態(tài)，在windows系統(tǒng)中可以打開(kāi)cmd然后進(jìn)入jdk所在目錄，然后執(zhí)行Jsp，能查看到各線程id，然后執(zhí)行jstack -F pid就可以看的狀態(tài)了

可以看到幾個(gè)Thread state是BLOCKED，就是阻塞了，什么原因呢？

尷尬發(fā)現(xiàn)flag變量和i變量前面忘記加volatile，導(dǎo)致flag和i被線程讀取修改時(shí)，其他線程不可見(jiàn)，所以才導(dǎo)致上面的問(wèn)題出現(xiàn)。

在JVM中每個(gè)線程讀取變量到cache中時(shí)相互都是不可見(jiàn)的，也就是java五大內(nèi)存區(qū)中的程序計(jì)數(shù)器區(qū)域?qū)τ诿總€(gè)線程都是獨(dú)立的不共享的，只有堆內(nèi)存區(qū)和方法區(qū)是對(duì)所有線程都是共享的。

當(dāng)線程1讀取了flag和i的值，并對(duì)其進(jìn)行修改的時(shí)候，線程2并發(fā)運(yùn)行，并不知道flag和i值已經(jīng)改變，導(dǎo)致多線程數(shù)據(jù)不一致的情況，所以加了volatile后，當(dāng)線程讀取變量進(jìn)行修改后會(huì)“通知”其它線程這個(gè)值已經(jīng)進(jìn)行了修改。

import java.util.concurrent.atomic.AtomicInteger; 
public class ThreadTest {
 private volatile int i=0;
 private Thread thread1,thread2,thread3;
 private volatile int flag=0;
 public void runThread() throws InterruptedException{
   thread1=new Thread(new Thread1());
   thread2=new Thread(new Thread2());
   thread3=new Thread(new Thread3());
   thread1.start();
   thread2.start();
   thread3.start();
 }
 public class Thread1 implements Runnable{
 
 public void run() {
  while(i<100){
  if(flag==0) {
   System.out.println("t1="+i);
   i++;
   flag=1;
  }
  }
 }
 
 }
 
 public class Thread2 implements Runnable{
 
 public void run() {
  
  while(i<100){
  if(flag==1){
   System.out.println("t2="+i);
   i++;
   flag=2;
  }
  }
 }
 
 }
 
 public class Thread3 implements Runnable{
 
 public void run() {
  
  while(i<100){
  if(flag==2){
   System.out.println("t3="+i);
   i++;
   flag=0;
  }
  }
 }
 
 }
}

運(yùn)行結(jié)果

-----未完-----

補(bǔ)充知識(shí)：Java n個(gè)線程輪流打印數(shù)字的問(wèn)題

一、兩個(gè)線程輪流打印數(shù)字。

加鎖實(shí)現(xiàn)：

package lianxi;
 
/*
 * 用鎖實(shí)現(xiàn)兩個(gè)線程輪流打印1——100
 */
public class Print1TO100TwoThread {
 private Object lock = new Object();
 private int i = 0;
 
 Thread threadA = new Thread(new Runnable() {
 @Override
 public void run() {
  while (i <= 100) {
  synchronized (lock) {
 
   try {
   if (i > 100)
    break;
   System.out.println("threadA :" + (i++));
   lock.notify();
   lock.wait();
   } catch (InterruptedException e) {
   e.printStackTrace();
   }
  }
  }
 }
 
 });
 
 Thread threadB = new Thread(new Runnable() {
 @Override
 public void run() {
  while (i <= 100) {
  synchronized (lock) {
 
   try {
   if (i > 100)
    break;
   System.out.println("threadB :" + (i++));
   lock.notify();
   lock.wait();
   } catch (InterruptedException e) {
   e.printStackTrace();
   }
  }
  }
 }
 });
 
 public void startTwoThread() throws InterruptedException {
 threadA.start();
 Thread.sleep(20);
 threadB.start();
 }
 public static void main(String[] args) throws InterruptedException {
 new Print1TO100TwoThread().startTwoThread();
 } 
}

用鎖效率太低，用一個(gè)變量來(lái)控制打印的順序。

package lianxi;
/*
 * 用兩個(gè)線程輪流打印1——10；用所實(shí)現(xiàn)效率太低，用變量來(lái)控制
 */
public class PrinntNumTwoThread {
 
 private volatile int num = 0;
 private volatile boolean flag = false;
 
 Thread threadA = new Thread(new Runnable() {
 
 @Override
 public void run() {
  while (true) {
  if (num > 10)
   return;
  if (!flag) {
   System.out.println("threadA-->" + ":" + (num++));
   flag = !flag;
  }
  }
 }
 
 });
 
 Thread threadB = new Thread(new Runnable() {
 @Override
 public void run() {
  while (true) {
  if (num > 10)
   return;
  if (flag) {
   System.out.println("threadB-->" + ":" + (num++));
   flag = !flag;
  }
  }
 }
 
 });
 
 public void startTwoThread() {
 threadA.start();
 threadB.start();
 }
 
 public static void main(String[] args) {
 new PrinntNumTwoThread().startTwoThread();
 }
}

二、那么如果要實(shí)現(xiàn)三個(gè)線程輪流打印1-100的數(shù)字呢？

package lianxi; 
public class PrintNumThreeThread {
 private volatile int i = 0;
 private volatile int flag = 0;
 Thread threadA = new Thread(new Runnable() {
 @Override
 public void run() {
  while (true) {
  if (i > 100)
   return;
  if (flag == 0) {
   System.out.println("threadA->" + ":" + (i++));
   flag = 1;
  }
  }
 }
 
 });
 
 Thread threadB = new Thread(new Runnable() {
 @Override
 public void run() {
  while (true) {
  if (i > 100)
   return;
  if (flag == 1) {
   System.out.println("threadB->" + ":" + (i++));
   flag = 2;
  }
  }
 }
 
 });
 
 Thread threadC = new Thread(new Runnable() {
 @Override
 public void run() {
  while (true) {
  if (i > 100)
   return;
  if (flag == 2) {
   System.out.println("threadC->" + ":" + (i++));
   flag = 0;
  }
  }
 }
 });
 
 public void startThreeThread() {
 threadA.start();
 threadB.start();
 threadC.start();
 }
 
 public static void main(String[] args) {
 new PrintNumThreeThread().startThreeThread();
 }
}

以上這篇Java實(shí)現(xiàn)多線程輪流打印1-100的數(shù)字操作就是小編分享給大家的全部?jī)?nèi)容了，希望能給大家一個(gè)參考，也希望大家多多支持腳本之家。

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