首页 / 面试 / Java线程进阶知识-面试必备
Java线程进阶知识-面试必备
内容导读
互联网集市收集整理的这篇技术教程文章主要介绍了Java线程进阶知识-面试必备,小编现在分享给大家,供广大互联网技能从业者学习和参考。文章包含40791字,纯文字阅读大概需要59分钟。
内容图文
![Java线程进阶知识-面试必备](/upload/InfoBanner/zyjiaocheng/625/7ea51b2a602b45a1ad6e450e79c3fcb7.jpg)
多线程进阶JUC
1.什么是JUC
java.util 工具包,包,分类
业务:普通的线程代码 Thread
Runnable:没有返回值,相对效率较低
我们使用Callable
2.线程和进程
进程: 一个程序
一个进程可以包含多个线程,至少包含一个
Java真的可以开启线程吗?不可以
public synchronized void start() {
/**
* This method is not invoked for the main method thread or "system"
* group threads created/set up by the VM. Any new functionality added
* to this method in the future may have to also be added to the VM.
*
* A zero status value corresponds to state "NEW".
*/
if (threadStatus != 0)
throw new IllegalThreadStateException();
/* Notify the group that this thread is about to be started
* so that it can be added to the group's list of threads
* and the group's unstarted count can be decremented. */
group.add(this);
boolean started = false;
try {
start0();
started = true;
} finally {
try {
if (!started) {
group.threadStartFailed(this);
}
} catch (Throwable ignore) {
/* do nothing. If start0 threw a Throwable then
it will be passed up the call stack */
}
}
}
并发和并行
并发编程:(多线程操作同一个资源)
CPU
public class Test1 {
public static void main(String[] args) {
// 获取CPU的核数
// CPU密集型,IO密集型
System.out.println(Runtime.getRuntime().availableProcessors());
}
}
并发编程的本质: 充分利用CPU的资源
并行: (多个人一起行走)
线程有几个状态:
public enum State {
//新生
NEW,
//运行
RUNNABLE,
//阻塞
BLOCKED,
//等待
WAITING,
//超时等待
TIMED_WAITING,
//终止
TERMINATED;
}
wait和sleep的区别
1.来自不同的类
wait---object
sleep--Thread
2.关于锁的释放
wait会释放锁,sleep不会释放
3.使用的范围不同
wait 必须在同步代码块中使用
sleep 可以在任何地方使用
4.是否需要捕获异常
wait 不是必须捕获异常
sleep 必须捕获异常
3.Lock锁(重点)
传统方式 synchronized
lock接口
![Java线程进阶知识-面试必备 - 文章图片](/upload/getfiles/0001/2021/5/1/20210501034815752.jpg)
Lock锁
![Java线程进阶知识-面试必备 - 文章图片](/upload/getfiles/0001/2021/5/1/20210501034816618.jpg)
公平锁:十分公平,先来后到
非公平锁:十分不公平:可以插队(默认)
package com.lei.demo1;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
- @ClassName SaleTicketDemo2
- @Description: TODO
- @Author 1689169874@qq.com
- @Date 2020/7/23/023 16:51
- @Version 1.0
**/
public class SaleTicketDemo2 {
public static void main(String[] args) {
//并发:多线程操作 ,把资源丢入线程
final Ticket ticket = new Ticket();
new Thread(()->{
for (int i = 0; i < 60; i++) {
ticket.sale();
}
}, "A").start();
new Thread(()->{
for (int i = 0; i < 60; i++) {
ticket.sale();
}
}, "B").start();new Thread(()->{
for (int i = 0; i < 60; i++) {
ticket.sale();
}
}, "C").start();
}
}
//lock锁
//三部曲 1.新建锁 2.加锁 3.解锁
class Ticket2 {
private int number = 50;
Lock lock = new ReentrantLock();
public void sale() {
lock.lock(); //加锁
try {
//业务代码
if (number > 0) {
System.out.println(Thread.currentThread().getName() + " 卖出了第" + (number--) + "票,剩余" + number);
}
} catch (Exception e) {
e.printStackTrace();
} finally {
//解锁
lock.unlock();
}
}
}
synchronized 和 Lock 区别
1.synchronized 内置的java关键字,Lock是一个java 类
2.synchronized 无法判断获取锁的状态,Lock可以判断是否获取到了锁
3.synchronized 会自动释放锁,Lock必须说动释放锁,如果不释放锁,会死锁
4.synchronized 线程1获得锁,阻塞,线程2就会一直等待;Lock锁就不一定会等待下去
5.synchronized 可重入锁,不可以中断的,非公平;Lock,可重入锁,可以判断锁,非公平(但是可以自己设置)
6.synchronized 适合锁少量的代码问题,Lock适合锁大量的代码。
锁是什么,如何判断锁的是谁
4.生产者和消费者问题
synchronized wait notify
package com.lei.PC;
/**
- @ClassName A
- @Description: TODO
- @Author 1689169874@qq.com
- @Date 2020/7/23/023 17:08
- @Version 1.0
**/
import jdk.nashorn.internal.ir.IfNode;
import javax.xml.crypto.Data;
/**
- 线程之间的通信问题:生产者和消费者之间的问题: 等待唤醒和通知唤醒
- 线程交替进行 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) {
MyData myData = new MyData();
new Thread(()->{
for (int i = 0; i < 10; i++) {
try {
myData.increment();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
},"A").start();
new Thread(()->{
for (int i = 0; i < 10; i++) {
try {
myData.decrement();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
},"B").start();
}
}
//判断等待,业务,通知
class MyData{
private int num = 0;
//+1
public synchronized void increment() throws InterruptedException {
if (num!=0){
//等待
this.wait();
}
num++;
this.notifyAll();
System.out.println(Thread.currentThread().getName()+"-->"+num);
}
//-1
public synchronized void decrement() throws InterruptedException {
if (num==0){
// 等待
this.wait();
}
num--;
//通知
this.notifyAll();
System.out.println(Thread.currentThread().getName()+"-->"+num);
}
}
问题存在===>更多的线程安全吗? 因为我们使用了notifAll()
![Java线程进阶知识-面试必备 - 文章图片](/upload/getfiles/0001/2021/5/1/20210501034817056.jpg)
if 改为 while
JUC版本的生产者和消费者
![Java线程进阶知识-面试必备 - 文章图片](/upload/getfiles/0001/2021/5/1/20210501034817395.jpg)
通过Lock找到 Condition
![Java线程进阶知识-面试必备 - 文章图片](/upload/getfiles/0001/2021/5/1/20210501034817681.jpg)
代码实现:
package com.lei.PC;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
-
@ClassName B
-
@Description: TODO
-
@Author 1689169874@qq.com
-
@Date 2020/7/23/023 17:26
-
@Version 1.0
**/
public class B {
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();
}
static class Data {
private int num = 0;
Lock lock = new ReentrantLock();
Condition condition = lock.newCondition();
//+1
// condition.await(); //等待
// condition.signalAll(); //唤醒
public void increment() throws InterruptedException {
lock.lock();
try {
//业务代码
while (num != 0) {
condition.await();
}
num++;
System.out.println(Thread.currentThread().getName() + "-->" + num);
condition.signalAll();
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
//-1
public void decrement() throws InterruptedException {
lock.lock();
try {
while (num == 0) {
// 等待
condition.await();
}
num--;
//通知
condition.signalAll();
System.out.println(Thread.currentThread().getName() + "-->" + num);
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
}
}
Condition 精准的通知和唤醒线程
![Java线程进阶知识-面试必备 - 文章图片](/upload/getfiles/0001/2021/5/1/20210501034818191.jpg)
代码测试:
package com.lei.PC;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
-
@ClassName C
-
@Description: TODO
-
@Author 1689169874@qq.com
-
@Date 2020/7/23/023 20:53
@Version 1.0
**/
public class C {
public static void main(String[] args) {
Data2 data2 = new Data2();
new Thread(() -> {
for (int i = 0; i < 10; i++) {
data2.printA();
}
}, "A").start();
new Thread(() -> {
for (int i = 0; i < 10; i++) {
data2.printB();
}
}, "B").start();
new Thread(() -> {
for (int i = 0; i < 10; i++) {
data2.printC();
}
}, "C").start();
}
}
//A-> B -> C
class Data2 {
private Lock lock = new ReentrantLock();
Condition condition1 = lock.newCondition();
Condition condition2 = lock.newCondition();
Condition condition3 = lock.newCondition();
private int num = 1;
public void printA() {
lock.lock();
try {
//业务代码, 判断 ,执行,通知
while (num!=1){
//等待
condition1.await();
}
System.out.println(Thread.currentThread().getName()+"=>AAAA");
//唤醒指定的人 B
num=2;
condition2.signal();
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
public void printB() {
lock.lock();
try {
while (num!=2){
condition2.await();
}
System.out.println(Thread.currentThread().getName()+"=>BBBB");
num=3;
condition3.signal();
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
public void printC() {
lock.lock();
try {
while (num!=3){
condition3.await();
}
System.out.println(Thread.currentThread().getName()+"=>CCCC");
num=1;
condition1.signal();
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
}
5.8锁现象
如何判断锁的是谁? 永远知道是什么锁,锁到底锁的是谁?
深刻理解我们的锁
package com.lei.lock8;
/**
- @ClassName Test1
- @Description: TODO
- @Author 1689169874@qq.com
- @Date 2020/7/23/023 22:56
- @Version 1.0
**/
import java.util.concurrent.TimeUnit;
/**
- 8锁,就是关于锁的8个问题
- 1、标准情况下,两个线程发短信和打电话谁先打印?
2、发短信(内部延迟4秒)情况下,两个线程发短信和打电话谁先打印?
*/
public class Test1 {
public static void main(String[] args) {
Phone phone = new Phone();
//锁的存在
new Thread(()->{
phone.sendMsg();
},"A").start();
try {
TimeUnit.SECONDS.sleep(1);
} catch (InterruptedException e) {
e.printStackTrace();
}
new Thread(() ->{
phone.call();
},"B").start();
}
}
class Phone{
//synchronized 锁的对象是锁的调用者
// 两个方法用的是同一个锁,谁先拿到谁执行
public synchronized void sendMsg(){
try {
TimeUnit.SECONDS.sleep(2);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("发短信");
}
public synchronized void call(){
System.out.println("打电话");
}
}
package com.lei.lock8;
import java.util.concurrent.TimeUnit;
/**
- @ClassName Test2
- @Description: TODO
- @Author 1689169874@qq.com
- @Date 2020/7/23/023 23:42
- @Version 1.0
**/
/**
-
3.增加了一个普通方法后,是先执行hello还是先发短信?
-
4.两个对象,两个同步方法,发短信还是打电话
*/
public class Test2 {
public static void main(String[] args) {
//两个对象,两个调用者,两把锁
Phone2 phone1 = new Phone2();
Phone2 phone2 = new Phone2();
//锁的存在
new Thread(() -> {
phone1.sendMsg();
}, "A").start();
try {
TimeUnit.SECONDS.sleep(1);
} catch (InterruptedException e) {
e.printStackTrace();
}
new Thread(() -> {
phone2.call();
}, "B").start();
}
}
class Phone2 {
//synchronized 锁的对象是锁的调用者
// 两个方法用的是同一个锁,谁先拿到谁执行
public synchronized void sendMsg() {
try {
TimeUnit.SECONDS.sleep(2);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("发短信");
}
public synchronized void call() {
System.out.println("打电话");
}
// 这里没有锁,不受锁的影响
public void hello(){
System.out.println("hello");
}
}
package com.lei.lock8;
import java.util.concurrent.TimeUnit;
/**
* @ClassName Test3
* @Description: TODO
* @Author 1689169874@qq.com
* @Date 2020/7/23/023 23:49
* @Version 1.0
**/
/**
* 5.增加两个静态的同步方法,只有一个对象,发短信和打电话?
* 6.两个对象,增加两个同步的教态方法,先发短信还是打电话?
*/
public class Test3 {
public static void main(String[] args) {
//两个对象,两个调用者,两把锁
//两个对象的类都是同一个,static,锁的是Class
Phone3 phone1 = new Phone3();
Phone3 phone2 = new Phone3();
//锁的存在
new Thread(() -> {
Phone3.sendMsg();
}, "A").start();
try {
TimeUnit.SECONDS.sleep(1);
} catch (InterruptedException e) {
e.printStackTrace();
}
new Thread(() -> {
Phone3.call();
}, "B").start();
}
}
class Phone3 {
//synchronized 锁的对象是锁的调用者
// 两个方法用的是同一个锁,谁先拿到谁执行
// static 静态方法
// 类一加载就有了,锁的是Class
public static synchronized void sendMsg() {
try {
TimeUnit.SECONDS.sleep(2);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("发短信");
}
public static synchronized void call() {
System.out.println("打电话");
}
}
package com.lei.lock8;
import java.util.concurrent.TimeUnit;
/**
* @ClassName Test4
* @Description: TODO
* @Author 1689169874@qq.com
* @Date 2020/7/23/023 23:56
* @Version 1.0
**/
/**
* 7.一个静态同步方法,一个普通同步方法,先打印 发短信,打电话?
* 8.两个对象,一个静态同步方法,一个普通同步方法,先打印 发短信,打电话?
*
*/
public class Test4 {
public static void main(String[] args) {
//两个对象,两个调用者,两把锁
//两个对象的类都是同一个,static,锁的是Class
Phone4 phone1 = new Phone4();
Phone4 phone2 = new Phone4();
//锁的存在
new Thread(() -> {
Phone4.sendMsg();
}, "A").start();
try {
TimeUnit.SECONDS.sleep(1);
} catch (InterruptedException e) {
e.printStackTrace();
}
new Thread(() -> {
phone2.call();
}, "B").start();
}
}
class Phone4 {
// 静态的同步方法
public static synchronized void sendMsg() {
try {
TimeUnit.SECONDS.sleep(2);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("发短信");
}
//普通的同步方法
public synchronized void call() {
System.out.println("打电话");
}
}
小结
new this 具体的一个属性
static Class 唯一的一个模板
6.集合类不安全
List不安全
package com.lei.unsafe;
import java.util.*;
import java.util.concurrent.CopyOnWriteArrayList;
//java.util.ConcurrentModificationException 并发修改异常!
/**
-
@ClassName ListTest
-
@Description: TODO
-
@Author 1689169874@qq.com
-
@Date 2020/7/24/024 0:04
@Version 1.0
/
public class ListTest {
public static void main(String[] args) {
//并发下,ArrayList 不是安全的
/
* 解决方案:
* 1.List<String> list = new Vector<>();
* 2.List<String> list = Collections.synchronizedList(new ArrayList<>());
* 3.List<String> list = new CopyOnWriteArrayList<>();
*/
//CopyOnWrite 写入是复刻, COW 计算机程序设计领域的一种优化策略
// 多个线程调用的时候,list,读取的时候,固定的,写入(覆盖)
//避免在写入的时候覆盖, 造成数据问题!
// 读写分离 MyCat
// CopyOnWriteArrayList比Vector好在哪里?
List<String> list = new CopyOnWriteArrayList<>();
for (int i = 0; i < 10; i++) {
new Thread(() -> {
list.add(UUID.randomUUID().toString().substring(0, 5));
System.out.println(list);
}, String.valueOf(i)).start();
}
}
}
学习方法:1.先会用 2,寻找其他解决方案 3.分析源码
set不安全
package com.lei.unsafe;
import java.util.*;
import java.util.concurrent.CopyOnWriteArraySet;
/**
- @ClassName SetTest
- @Description: TODO
- @Author 1689169874@qq.com
- @Date 2020/7/24/024 0:22
- @Version 1.0
**/
/**
- 同理可证: java.util.ConcurrentModificationException
- 1.Set<String> set = Collections.synchronizedSet(new HashSet<>());
- 2.Set<String> set = new CopyOnWriteArraySet<>();
*/
public class SetTest {
public static void main(String[] args) {
// Set<String > set = new HashSet<>();
// Set<String> set = Collections.synchronizedSet(new HashSet<>());
Set<String> set = new CopyOnWriteArraySet<>();
for (int i = 0; i < 100; i++) {
new Thread(() -> {
set.add(UUID.randomUUID().toString().substring(0,4));
System.out.println(set);
},String.valueOf(i)).start();
}
}
}
HashSet底层是什么?
public HashSet() {
map = new HashMap<>();
}
//add set 本质是map ,key是无法重复的!
public boolean add(E e) {
return map.put(e, PRESENT)==null;
}
// PRESENT是一个不变的值
private static final Object PRESENT = new Object();
HashMap
package com.lei.unsafe;
import java.util.HashMap;
import java.util.Map;
import java.util.UUID;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.CopyOnWriteArrayList;
/**
- @ClassName MapTest
- @Description: TODO
- @Author 1689169874@qq.com
- @Date 2020/7/24/024 0:34
- @Version 1.0
**/
/**
- java.util.ConcurrentModificationException
-
*/
public class MapTest {
public static void main(String[] args) {
// Map<String ,String> map = new HashMap<>();
Map<String ,String> map = new ConcurrentHashMap<>();
//加载因子,初始化容量
for (int i = 0; i < 40; i++) {
new Thread(() -> {
map.put(Thread.currentThread().getName(), UUID.randomUUID().toString().substring(0,4));
System.out.println(map);
}).start();
}
}
}
7.Callable( 简单 )
类似于Runnable
1.可以有返回值
2.可以抛出异常
3.方法不同 run() /call()
代码测试
package com.lei.callable;
import java.util.concurrent.Callable;
import java.util.concurrent.FutureTask;
/**
- @ClassName CallableTest
- @Description: TODO
- @Author 1689169874@qq.com
- @Date 2020/7/24/024 9:53
- @Version 1.0
**/
public class CallableTest {
public static void main(String[] args) throws Exception {
// new Thread(new Runnable()).start(); //怎么启动Callable
// new Thread(new FutureTask<V>()).start(); //怎么启动Callable
// new Thread(new FutureTask<V>(Callable)).start(); //怎么启动Callable
// new Thread().start(); //怎么启动Callable
MyThread myThread = new MyThread();
FutureTask<Integer> futureTask = new FutureTask<>(myThread);
new Thread(futureTask,"A").start();
Integer o = futureTask.get();
System.out.println(o);
}
}
class MyThread implements Callable<Integer> {
@Override
public Integer call() {
System.out.println("call");
return 123;
}
}
细节
1.有缓存
2.结果可能需要等待,会阻塞
8.常用的辅助类
8.1、CountDownLatch
![Java线程进阶知识-面试必备 - 文章图片](/upload/getfiles/0001/2021/5/1/20210501034818420.jpg)
代码:
package com.lei.add;
/**
- @ClassName CountDownLatchDemo
- @Description: TODO
- @Author 1689169874@qq.com
- @Date 2020/7/24/024 14:03
- @Version 1.0
**/
import java.util.concurrent.CountDownLatch;
/**
-
计数器
*/
public class CountDownLatchDemo {
public static void main(String[] args) throws InterruptedException {
//总数是6,必须是执行任务的时候使用
CountDownLatch countDownLatch = new CountDownLatch(6);
for (int i = 0; i < 6; i++) {
new Thread(() -> {
System.out.println(Thread.currentThread().getName()+"Go out");
countDownLatch.countDown();
},String.valueOf(i)).start();
}
countDownLatch.await();// 等待计数器归零,然后再向下执行
System.out.println("Close Door");
// countDownLatch.countDown(); // -1
}
}
原理:减法计数器
countDownLatch.countDown();
//数量-1
countDownLatch.await();
// 等待计数器归零,然后再向下执行
每次有线程调用countDown()数量-1,假设计数器变为0,countDownLatch.await()就会被唤醒,继续执行
8.2、CyclicBarrier
加法计数器
代码:
package com.lei.add;
import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;
/**
- @ClassName CyclicBarrierDemo
- @Description: TODO
- @Author 1689169874@qq.com
- @Date 2020/7/24/024 14:17
@Version 1.0
/
public class CyclicBarrierDemo {
public static void main(String[] args) {
/
* 集齐七颗龙珠
*/
CyclicBarrier cyclicBarrier = new CyclicBarrier(7, () -> {
System.out.println("召唤神龙成功");
});
for (int i = 0; i < 7; i++) {
//lambda
final int temp = i;
new Thread(() -> {
System.out.println(Thread.currentThread().getName()+"收集" +temp + "个龙珠");
try {
cyclicBarrier.await();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (BrokenBarrierException e) {
e.printStackTrace();
}
}).start();
}
}
}
8.3、Semaphore
Semaphore:信号量
![Java线程进阶知识-面试必备 - 文章图片](/upload/getfiles/0001/2021/5/1/20210501034819028.jpg)
代码
package com.lei.add;
import java.util.concurrent.Semaphore;
import java.util.concurrent.TimeUnit;
/**
-
@ClassName SemaphoreDemo
-
@Description: TODO
-
@Author 1689169874@qq.com
-
@Date 2020/7/24/024 14:23
-
@Version 1.0
**/
public class SemaphoreDemo {
public static void main(String[] args) {
//线程数量: 停车位
Semaphore semaphore = new Semaphore(3);
for (int i = 0; i < 6; i++) {
new Thread(() -> {
//acquire() 阻塞
try {
semaphore.acquire();
System.out.println(Thread.currentThread().getName()+"抢到车位");
TimeUnit.SECONDS.sleep(2);
System.out.println(Thread.currentThread().getName()+"离开车位");
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
semaphore.release();
}
//release() 释放
},String.valueOf(i)).start();
}
}
}
原理:
![Java线程进阶知识-面试必备 - 文章图片](/upload/getfiles/0001/2021/5/1/20210501034819199.jpg)
9.读写锁
ReadWriteLock
![Java线程进阶知识-面试必备 - 文章图片](/upload/getfiles/0001/2021/5/1/20210501034819430.jpg)
测试:
package com.lei.rw;
/**
- @ClassName ReadWriteLockDemo
- @Description: TODO
- @Author 1689169874@qq.com
- @Date 2020/7/24/024 14:30
- @Version 1.0
**/
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;
/**
-
ReadWriteLock
*/
public class ReadWriteLockDemo {
public static void main(String[] args) {
MyCache2 myCache = new MyCache2();
//写入
for (int i = 0; i < 5; i++) {
final int temp = i;
new Thread(() -> myCache.put(temp+"",temp+""),String.valueOf(i)).start();
}
for (int i = 0; i < 5; i++) {
final int temp = i;
new Thread(() -> myCache.get(temp+""),String.valueOf(i)).start();
}
}
}
/**
-
自定义缓存
*/
class MyCache {
private volatile Map<String, Object> map = new HashMap<>();
//存,写
public void put(String key, Object value) {
System.out.println(Thread.currentThread().getName() + "写入" + key);
map.put(key, value);
System.out.println(Thread.currentThread().getName() + "写入ok");
}
// 取,写
public void get(String key) {
System.out.println(Thread.currentThread().getName() + "读取" + key);
Object o = map.get(key);
System.out.println(Thread.currentThread().getName() + "读取ok");
}
}
/**
自定义缓存 加锁
*/
class MyCache2 {
private volatile Map<String, Object> map = new HashMap<>();
//读写锁,更加细腻的控制
ReadWriteLock readWriteLock = new ReentrantReadWriteLock();
//写入的时候只希望同时只有一个线程写
//存,写
public void put(String key, Object value) {
readWriteLock.writeLock().lock();
System.out.println(Thread.currentThread().getName() + "写入" + key);
map.put(key, value);
System.out.println(Thread.currentThread().getName() + "写入ok");
readWriteLock.writeLock().unlock();
}
// 取,写
public void get(String key) {
readWriteLock.readLock().lock();
System.out.println(Thread.currentThread().getName() + "读取" + key);
Object o = map.get(key);
System.out.println(Thread.currentThread().getName() + "读取ok");
readWriteLock.readLock().unlock();
}
}
10、阻塞队列
![Java线程进阶知识-面试必备 - 文章图片](/upload/getfiles/0001/2021/5/1/20210501034819646.jpg)
BlockingQueue 不是新的东西
什么情况下我们会使用阻塞队列:多线程,线程池
![Java线程进阶知识-面试必备 - 文章图片](/upload/getfiles/0001/2021/5/1/20210501034819966.jpg)
学会使用队列
添加,移除
四组API
方式 抛出异常 不会抛出异常,有返回值 阻塞 等待 超时等待
添加 add offer() put() offer( , ) 移除 remove poll() take() poll( , ) 检测队首元素 element() peek
package com.lei.bq;
import com.lei.lock8.Test1;
import java.util.ArrayList;
import java.util.Collection;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.TimeUnit;
/**
-
@ClassName BlockingQueueDemo
-
@Description: TODO
-
@Author 1689169874@qq.com
-
@Date 2020/7/24/024 15:00
@Version 1.0
**/
public class BlockingQueueDemo {
public static void main(String[] args) throws InterruptedException {
// test1();
// test2();
// test3();
test4();
}
/**
- 抛出异常
*/
public static void test1() {
//队列的大小
ArrayBlockingQueue blockingQueue = new ArrayBlockingQueue<>(3);
System.out.println(blockingQueue.add("q"));
System.out.println(blockingQueue.add("b"));
System.out.println(blockingQueue.add("c"));
System.out.println("===========");
System.out.println(blockingQueue.remove());
System.out.println(blockingQueue.remove());
System.out.println(blockingQueue.remove());
}
/**
- 不抛出异常,有返回值
*/
public static void test2() {
ArrayBlockingQueue arrayBlockingQueue = new ArrayBlockingQueue<>(3);
System.out.println(arrayBlockingQueue.offer("a"));
System.out.println(arrayBlockingQueue.offer("b"));
System.out.println(arrayBlockingQueue.offer("c"));
System.out.println(arrayBlockingQueue.offer("e")); //false 不抛出异常
System.out.println("=============");
System.out.println(arrayBlockingQueue.poll());
System.out.println(arrayBlockingQueue.element());
System.out.println(arrayBlockingQueue.poll());
System.out.println(arrayBlockingQueue.poll());
System.out.println(arrayBlockingQueue.poll()); // null 不抛出异常
}
/**
- 等待,阻塞 (一直)
*/
public static void test3() throws InterruptedException {
ArrayBlockingQueue blockingQueue = new ArrayBlockingQueue<>(3);
//一直阻塞
blockingQueue.put("a");
blockingQueue.put("b");
blockingQueue.put("c");
System.out.println(blockingQueue.take());
System.out.println(blockingQueue.take());
System.out.println(blockingQueue.take());
System.out.println(blockingQueue.take()); //没有这个元素,一直阻塞
}
public static void test4() throws InterruptedException {
ArrayBlockingQueue blockingQueue = new ArrayBlockingQueue<>(3 );
blockingQueue.offer("a");
blockingQueue.offer("a");
blockingQueue.offer("a");
blockingQueue.offer("d", 2,TimeUnit.SECONDS);//
System.out.println("===============");
System.out.println(blockingQueue.poll());
System.out.println(blockingQueue.poll());
System.out.println(blockingQueue.poll());
System.out.println(blockingQueue.poll(2, TimeUnit.SECONDS));
}
}
SynchronizeQueue 同步队列>
没有容量,
进去一个元素,必须等待取出来后,才能再往里面放一个元素
put take
package com.lei.bq;
/**
- @ClassName SynchronizeQueueDemo
- @Description: TODO
- @Author 1689169874@qq.com
- @Date 2020/7/24/024 16:29
- @Version 1.0
**/
import java.util.concurrent.SynchronousQueue;
import java.util.concurrent.TimeUnit;
/**
同步队列
*/
public class SynchronizeQueueDemo {
public static void main(String[] args) {
SynchronousQueue<String> synchronousQueue = new SynchronousQueue<>();
new Thread(() -> {
try {
System.out.println(Thread.currentThread().getName() + " put 1");
synchronousQueue.put("1");
System.out.println(Thread.currentThread().getName() + " put 2");
synchronousQueue.put("2");
System.out.println(Thread.currentThread().getName() + " put 3");
synchronousQueue.put("3");
} catch (InterruptedException e) {
e.printStackTrace();
}
},"T1").start();
new Thread(() -> {
try {
TimeUnit.SECONDS.sleep(3);
System.out.println(Thread.currentThread().getName() + "=>"+synchronousQueue.take());
TimeUnit.SECONDS.sleep(3);
System.out.println(Thread.currentThread().getName()+ "=>" + synchronousQueue.take());
TimeUnit.SECONDS.sleep(3);
System.out.println(Thread.currentThread().getName()+ "=>" + synchronousQueue.take());
} catch (InterruptedException e) {
e.printStackTrace();
}
},"T2").start();
}
}
11.线程池(重点)
线程池:三大方法,七大参数,四种拒绝策略
程序运行的本质: 占用系统的资源,优化资源的使用 =》池化技术
线程池:内存池,对象池
池化技术: 事先准备好资源,有人要用,就来我这里拿,用完之后还给我。
线程池的好处:
- 降低资源的消耗
- 提高响应的速度
- 方便管理
==线程可以复用,可以控制最大并发数,管理线程==
线程池必会技术,
![Java线程进阶知识-面试必备 - 文章图片](/upload/getfiles/0001/2021/5/1/20210501034820211.jpg)
三大方法
package com.lei.pool;
import java.util.concurrent.Executor;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
/**
- @ClassName Demo1
- @Description: TODO
- @Author 1689169874@qq.com
- @Date 2020/7/24/024 16:46
- @Version 1.0
**/
public class Demo1 {
public static void main(String[] args) {
// ExecutorService executorService = Executors.newSingleThreadExecutor();//单个线程
//// Executors.newFixedThreadPool(5); //单个线程
//// Executors.newCachedThreadPool(); //单个线程
// for (int i = 0; i < 10; i++) {
// new Thread().start();
// }
ExecutorService service = Executors.newSingleThreadExecutor();
for (int i = 0; i < 10; i++) {
service.execute(
() -> {
// ... do something inside runnable task
System.out.println(Thread.currentThread().getName()+" ok");
});
}
service.shutdown();
}
}
七大参数
public static ExecutorService newSingleThreadExecutor() {
return new FinalizableDelegatedExecutorService
(new ThreadPoolExecutor(1, 1,
0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue<Runnable>()));
}
public static ExecutorService newFixedThreadPool(int nThreads) {
return new ThreadPoolExecutor(nThreads, nThreads,
0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue<Runnable>());
}
public static ExecutorService newCachedThreadPool() {
return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
60L, TimeUnit.SECONDS,
new SynchronousQueue<Runnable>());
}
//本质 :ThreadPoolExecutor()
public ThreadPoolExecutor(int corePoolSize, //核心线程大小
int maximumPoolSize, //最大核心线程大小
long keepAliveTime, //超时了没有人就会调用
TimeUnit unit, // 超时单位
BlockingQueue<Runnable> workQueue, //阻塞队列
ThreadFactory threadFactory, //线程工厂,创建线程的,一般不用动
RejectedExecutionHandler handler) //拒绝策略 {
if (corePoolSize < 0 ||
maximumPoolSize <= 0 ||
maximumPoolSize < corePoolSize ||
keepAliveTime < 0)
throw new IllegalArgumentException();
if (workQueue == null || threadFactory == null || handler == null)
throw new NullPointerException();
this.acc = System.getSecurityManager() == null ?
null :
AccessController.getContext();
this.corePoolSize = corePoolSize;
this.maximumPoolSize = maximumPoolSize;
this.workQueue = workQueue;
this.keepAliveTime = unit.toNanos(keepAliveTime);
this.threadFactory = threadFactory;
this.handler = handler;
}
![Java线程进阶知识-面试必备 - 文章图片](/upload/getfiles/0001/2021/5/1/20210501034820486.jpg)
手动创建一个线程池
拒绝策略:
![Java线程进阶知识-面试必备 - 文章图片](/upload/getfiles/0001/2021/5/1/20210501034820689.jpg)
四种拒绝策略
package com.lei.pool;
import java.util.concurrent.*;
/**
- @ClassName Demo1
- @Description: TODO
- @Author 1689169874@qq.com
- @Date 2020/7/24/024 16:46
- @Version 1.0
**/
public class Demo1 {
public static void main(String[] args) {
//自定义线程池 ! 工作中常用
ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(
2,
5,
3,
TimeUnit.SECONDS,
new LinkedBlockingQueue<>(3),
Executors.defaultThreadFactory(),
// new ThreadPoolExecutor.AbortPolicy()); //队列满了,抛出异常
// new ThreadPoolExecutor.CallerRunsPolicy()); //哪里来的回哪
// new ThreadPoolExecutor.DiscardPolicy());//队列满了,丢掉任务,不会抛出异常
new ThreadPoolExecutor.DiscardOldestPolicy());//队列满了,尝试竞争,不会抛出异常
//线程满了,还有人进来,不处理这个人的业务,抛出异常
//最大承载:Deque + max
//java.util.concurrent.RejectedExecutionException 超出
for (int i = 1; i <= 9 ; i++) {
threadPoolExecutor.execute(() -> {
System.out.println(Thread.currentThread().getName()+"ok");
});
}
threadPoolExecutor.shutdown();
}
}
小结和拓展
了解:CPU 密集型 IO密集型
//最大线程该如何定义
//1.CPU 密集型 几核,就是几,可以保持CPU的效率更高
// 2.IO 密集型
// 程序 15个大型任务线程,io十分占用资源
//获取CPU的核数
// System.out.println(Runtime.getRuntime().availableProcessors());
12、四大函数式接口(必须掌握)
1.函数式接口:只有一个方法的接口
@FunctionInterface
代码测试:
![Java线程进阶知识-面试必备 - 文章图片](/upload/getfiles/0001/2021/5/1/20210501034820887.jpg)
代码:
package com.lei.function;
import com.sun.org.apache.bcel.internal.generic.RET;
import java.util.function.Function;
/**
- @ClassName Demo01
- @Description: TODO
- @Author 1689169874@qq.com
- @Date 2020/7/24/024 20:02
@Version 1.0
**/
public class Demo01 {
public static void main(String[] args) {
//工具类,输出输入的值
// Function function = new Function<String,String>() {
// @Override
// public String apply(String str) {
// return str;
// }
// };
Function function = (str) -> {return str;};
System.out.println(function.apply("123"));
}
}
断定型接口
package com.lei.function;
import java.util.function.Predicate;
/**
- @ClassName Demo02
- @Description: TODO
- @Author 1689169874@qq.com
- @Date 2020/7/24/024 20:25
@Version 1.0
**/
public class Demo02 {
public static void main(String[] args) {
//判断字符串是否为空
// Predicate<String> predicate = new Predicate<String>() {
// @Override
// public boolean test(String s) {
// return s.isEmpty();
// }
// };
Predicate<String > predicate = (str) -> str.isEmpty();
System.out.println(predicate.test("123"));;
}
}
Consumer 消费型接口
package com.lei.function;
import java.sql.Connection;
import java.util.function.Consumer;
/**
- @ClassName Demo03
- @Description: TODO
- @Author 1689169874@qq.com
- @Date 2020/7/24/024 21:27
- @Version 1.0
**/
//消费性接口,只有输入,没有返回值
public class Demo03 {
public static void main(String[] args) {
// Consumer<String > consumer = new Consumer<String>() {
// @Override
// public void accept(String str) {
// System.out.println(str);
// }
// };
Consumer<String > consumer = (str) -> System.out.println(str);
consumer.accept("1234");
}
}
Supplier 供给型接口
package com.lei.function;
import java.util.function.Supplier;
/**
- @ClassName Demo04
- @Description: TODO
- @Author 1689169874@qq.com
- @Date 2020/7/24/024 21:57
@Version 1.0
**/
public class Demo04 {
public static void main(String[] args) {
// Supplier supplier = new Supplier<Integer>() {
// @Override
// public Integer get() {
// System.out.println("1234");
// return 1234;
// }
// };
Supplier supplier = () -> {return 12345;};
System.out.println(supplier.get());
}
}
13、Stream流式计算
什么是Stream流式计算
大数据: 存储+计算
集合、MySQL本质就是存储东西的
计算都应该交给流来操作!
package com.lei.stream;
import java.util.Arrays;
import java.util.List;
/**
- @ClassName Test
- @Description: TODO
- @Author 1689169874@qq.com
- @Date 2020/7/24/024 22:41
@Version 1.0
**/
public class Test {
public static void main(String[] args) {
User user1 = new User(1,"a",19);
User user2 = new User(2,"b",20);
User user3 = new User(3,"dsag",22);
User user4 = new User(4,"adsf",21);
//集合就是存储
List<User> userList = Arrays.asList(user1, user2, user3, user4);
//计算交给Stream流
userList.stream().filter(u -> {return u.getId()%2==0;}).
filter(u -> {return u.getAge()>20;}).
map(user->{return user.getName().toUpperCase();})
.sorted((uu1,uu2) -> {return uu2.compareTo(uu1);})
.limit(1).
forEach(System.out::println);
}
}
14、Forkjoin
分支合并
什么是ForkJoin?
ForkJoin在JDK1.7,并行执行任务,提高效率,大数据量!
大数据: Map Reduce(把大任务拆分为小任务)
![Java线程进阶知识-面试必备 - 文章图片](/upload/getfiles/0001/2021/5/1/20210501034821068.jpg)
ForkJoin特点:工作窃取
![Java线程进阶知识-面试必备 - 文章图片](/upload/getfiles/0001/2021/5/1/20210501034821222.jpg)
![Java线程进阶知识-面试必备 - 文章图片](/upload/getfiles/0001/2021/5/1/20210501034821488.jpg)
ForkJoin
package com.lei.forkjoin;
/**
- @ClassName ForkJoinDemo
- @Description: TODO
- @Author 1689169874@qq.com
- @Date 2020/7/27/027 23:43
- @Version 1.0
**/
import java.util.concurrent.RecursiveTask;
/**
-
求和计算的任务:
-
3000 6000(ForkJoin) 9000(Stream并行流水)
-
如何使用forkjoin
-
1、forkjoinpool
-
2、计算任务forkjoinpool.execute(ForkJoinTask <task>)
-
3、计算类要继承我们的ForkJoinTask
*/
public class ForkJoinDemo extends RecursiveTask<Long> {
private Long start;
private Long end;
public ForkJoinDemo(Long start, Long end) {
this.start = start;
this.end = end;
}
//临界值
private Long temp = 10000L;
//计算方法
@Override
protected Long compute() {
if ((end - start) > temp) {
//分支合并计算
Long sum = 0L;
for (Long i = start; i < end; i++) {
sum += i;
}
return sum;
} else { //ForkJoin
Long middle = (start - end) / 2; //中间值
ForkJoinDemo forkJoinDemo = new ForkJoinDemo(start, middle);
forkJoinDemo.fork(); //拆分任务,把任务压入线程队列
ForkJoinDemo forkJoinDemo1 = new ForkJoinDemo(middle + 1, end);
forkJoinDemo1.fork(); //拆分任务,把任务压入线程队列
return forkJoinDemo1.join() + forkJoinDemo.join();
}
}
}
测试:
package com.lei.forkjoin;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.ForkJoinTask;
import java.util.stream.LongStream;
/**
-
@ClassName Test
-
@Description: TODO
-
@Author 1689169874@qq.com
-
@Date 2020/7/28/028 12:55
-
@Version 1.0
**/
public class Test {
public static void main(String[] args) throws Exception {
// test1(); //7.463s
// test2(); //
test3();
}
//普通程序员
public static void test1(){
long start = System.currentTimeMillis();
Long sum = 0L;
for (Long i = 0L; i < 10_0000_0000; i++) {
sum+=i;
}
long end = System.currentTimeMillis();
System.out.println(sum);
System.out.println("耗时:"+((end-start) * 0.001) + "s");
}
//会使用ForkJoin
public static void test2() throws Exception{
long start = System.currentTimeMillis();
ForkJoinPool forkJoinPool = new ForkJoinPool();
ForkJoinDemo task = new ForkJoinDemo(0L, 10_0000_0000L);
ForkJoinTask<Long> submit = forkJoinPool.submit(task);// 提交任务
Long sum = submit.get();
long end = System.currentTimeMillis();
System.out.println(sum);
System.out.println("耗时:"+((end-start) * 0.001) + "s");
}
public static void test3(){
long start = System.currentTimeMillis();
//使用stream流
long sum = LongStream.rangeClosed(0L, 10_0000_0000L).parallel().reduce(0, Long::sum);
long end = System.currentTimeMillis();
System.out.println(sum);
System.out.println("耗时:"+(end-start) * 0.001 + "s");
}
}
15、异步回调
Future 设计的初衷: 对将来某个事件的结果进行建模
![Java线程进阶知识-面试必备 - 文章图片](/upload/getfiles/0001/2021/5/1/20210501034821687.jpg)
package com.lei.future;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
/**
-
@ClassName Demo01
-
@Description: 异步调用
-
// 异步执行
-
// 成功回调
-
// 失败回调
-
@Author 1689169874@qq.com
-
@Date 2020/7/28/028 13:16
@Version 1.0
**/
public class Demo01 {
public static void main(String[] args) throws ExecutionException, InterruptedException {
// 没有返回值的异步回调 runAsync 异步回调
// CompletableFuture<Void> completableFuture = CompletableFuture.runAsync(() -> {
// try {
// TimeUnit.SECONDS.sleep(2);
// } catch (InterruptedException e) {
// e.printStackTrace();
// }
// System.out.println(Thread.currentThread().getName());
// });
// System.out.println("111");
// completableFuture.get();// 获取阻塞执行结果
//有返回值的supplyAsync 异步回调
//ajax,成功和失败的回调
// 返回的是错误信息
CompletableFuture<Integer> completableFuture = CompletableFuture.supplyAsync(() -> {
System.out.println("completableFuture");
int i = 10/0;
return 1024;
});
completableFuture.whenComplete((t,u) -> {
System.out.println("t->"+t); //正常的返回结果
System.out.println("u->"+u); // 失败的返回结果
}).exceptionally((e) -> {
System.out.println(e.getMessage());
return 1234;
}).get();
}
}
16、JMM
请你谈谈你对Volatile的理解
Volatile是Java虚拟机提供的轻量级的同步机制
- 保证可见性
- ==不保证原子性==
- 禁止指令重排
什么是JMM
JMM : Java内存模型,不存在的东西,只是一个概念和约定
关于JMM的一些同步的约定
- 线程解锁前,必须把共享变量==立刻==刷回主存
- 线程加锁前,必须读取主存中的最新值到工作内存中
- 加锁和解锁是通一把锁
内存交互操作有8种,虚拟机实现必须保证每一个操作都是原子的,不可在分的(对于double和long类型的变量来说,load、store、read和write操作在某些平台上允许例外)
- lock (锁定):作用于主内存的变量,把一个变量标识为线程独占状态
- unlock (解锁):作用于主内存的变量,它把一个处于锁定状态的变量释放出来,释放后的变量才可以被其他线程锁定
- read (读取):作用于主内存变量,它把一个变量的值从主内存传输到线程的工作内存中,以便随后的load动作使用
- load (载入):作用于工作内存的变量,它把read操作从主存中变量放入工作内存中
- use (使用):作用于工作内存中的变量,它把工作内存中的变量传输给执行引擎,每当虚拟机遇到一个需要使用到变量的值,就会使用到这个指令
- assign (赋值):作用于工作内存中的变量,它把一个从执行引擎中接受到的值放入工作内存的变量副本中
- store (存储):作用于主内存中的变量,它把一个从工作内存中一个变量的值传送到主内存中,以便后续的write使用
- write (写入):作用于主内存中的变量,它把store操作从工作内存中得到的变量的值放入主内存的变量中
JMM对这八种指令的使用,制定了如下规则:
- 不允许read和load、store和write操作之一单独出现。即使用了read必须load,使用了store必须write
- 不允许线程丢弃他最近的assign操作,即工作变量的数据改变了之后,必须告知主存
- 不允许一个线程将没有assign的数据从工作内存同步回主内存
- 一个新的变量必须在主内存中诞生,不允许工作内存直接使用一个未被初始化的变量。就是怼变量实施use、store操作之前,必须经过assign和load操作
- 一个变量同一时间只有一个线程能对其进行lock。多次lock后,必须执行相同次数的unlock才能解锁
- 如果对一个变量进行lock操作,会清空所有工作内存中此变量的值,在执行引擎使用这个变量前,必须重新load或assign操作初始化变量的值
- 如果一个变量没有被lock,就不能对其进行unlock操作。也不能unlock一个被其他线程锁住的变量
- 对一个变量进行unlock操作之前,必须把此变量同步回主内存
问题:程序不知道主内存的值被修改了
17、Volatile
1、保证可见性
package com.lei.jmm;
import java.util.concurrent.TimeUnit;
/**
-
@ClassName JMMDemo
-
@Description: TODO
-
@Author 1689169874@qq.com
-
@Date 2020/7/28/028 19:54
-
@Version 1.0
**/
public class JMMDemo {
//不加 Volatile 程序就会死循环!
// 加 Volatile 可以保证可见性
private volatile static int num = 0;
public static void main(String[] args) {
new Thread(() -> { // 线程1对主内存的变化是不知道的
while (num == 0){
}
}).start();
try {
TimeUnit.SECONDS.sleep(1);
} catch (InterruptedException e) {
e.printStackTrace();
}
num = 1;
System.out.println(num);
}
}
2、不保证原子性
原子性: 不可分割
线程A在执行任务时,是不能被打扰的,也不能被分割,要么同时成功,要么同时失败
package com.lei.tvolatile;
/**
-
@ClassName volatileDemo
-
@Description: TODO
-
@Author 1689169874@qq.com
-
@Date 2020/7/28/028 20:06
@Version 1.0
**/
public class volatileDemo {
// volatile不保证原子性
private volatile static int num = 0;
public static void add() {
num++;
}
public static void main(String[] args) {
//理论上 num 的结果应该为 2万
for (int i = 0; i < 20; i++) {
new Thread(() -> {
for (int j = 0; j < 1000; j++) {
add();
}
}).start();
}
while (Thread.activeCount() > 2){
Thread.yield(); // 让出计算资源并重新竞争资源
}
System.out.println(Thread.currentThread().getName() + " " + num);
}
}
如果不加lock和synchronized ,怎么样保证原子性
![Java线程进阶知识-面试必备 - 文章图片](/upload/getfiles/0001/2021/5/1/20210501034821888.jpg)
使用原子类,解决原子性问题
package com.lei.future;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
/**
-
@ClassName Demo01
-
@Description: 异步调用
-
// 异步执行
-
// 成功回调
-
// 失败回调
-
@Author 1689169874@qq.com
-
@Date 2020/7/28/028 13:16
@Version 1.0
**/
public class Demo01 {
public static void main(String[] args) throws ExecutionException, InterruptedException {
// 没有返回值的异步回调 runAsync 异步回调
// CompletableFuture<Void> completableFuture = CompletableFuture.runAsync(() -> {
// try {
// TimeUnit.SECONDS.sleep(2);
// } catch (InterruptedException e) {
// e.printStackTrace();
// }
// System.out.println(Thread.currentThread().getName());
// });
// System.out.println("111");
// completableFuture.get();// 获取阻塞执行结果
//有返回值的supplyAsync 异步回调
//ajax,成功和失败的回调
// 返回的是错误信息
CompletableFuture<Integer> completableFuture = CompletableFuture.supplyAsync(() -> {
System.out.println("completableFuture");
int i = 10/0;
return 1024;
});
completableFuture.whenComplete((t,u) -> {
System.out.println("t->"+t); //正常的返回结果
System.out.println("u->"+u); // 失败的返回结果
}).exceptionally((e) -> {
System.out.println(e.getMessage());
return 1234;
}).get();
}
}
18、彻底玩转单例模式
内容总结
以上是互联网集市为您收集整理的Java线程进阶知识-面试必备全部内容,希望文章能够帮你解决Java线程进阶知识-面试必备所遇到的程序开发问题。
如果觉得互联网集市技术教程内容还不错,欢迎将互联网集市网站推荐给程序员好友。
内容备注
版权声明:本文内容由互联网用户自发贡献,该文观点与技术仅代表作者本人。本站仅提供信息存储空间服务,不拥有所有权,不承担相关法律责任。如发现本站有涉嫌侵权/违法违规的内容, 请发送邮件至 gblab@vip.qq.com 举报,一经查实,本站将立刻删除。
内容手机端
扫描二维码推送至手机访问。
来源:【匿名】