Java面试知识点：多线程

╰+攻爆jí腚メ 2022-09-09 15:59 205阅读 0赞

# 问题：Java面试知识点：多线程 #

答案：

1.线程

![watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBAeWFuZzEzNTYzNzU4MTI4_size_20_color_FFFFFF_t_70_g_se_x_16][]

![watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBAeWFuZzEzNTYzNzU4MTI4_size_20_color_FFFFFF_t_70_g_se_x_16 1][]

代码如下：

package com.xy;
    
    /**
     * @ProjectName: day01
     * @Package: com.xy
     * @ClassName: test01
     * @Author: 杨路恒
     * @Description:
     * @Date: 2021/8/25 0025 16:57
     * @Version: 1.0
     */
    public class test01 {
        public static void main(String[] args) {
            MyThread myThread=new MyThread();
            MyThread myThread1=new MyThread();
            myThread.start();
            myThread1.start();
        }
    }
    
    
    
    
    public class test02 {
        public static void main(String[] args) {
            MyRunnable mr=new MyRunnable();     //创建了一个参数对象
            Thread t=new Thread(mr);            //创建了一个线程对象，并把参数传递给这个线程
            t.start();
            MyRunnable mr1=new MyRunnable();
            Thread t1=new Thread(mr1);            //创建了一个线程对象，并把参数传递给这个线程
            t1.start();
        }
    }
    
    public class MyRunnable implements Runnable {
        @Override
        public void run() {
            for (int i = 0; i < 100; i++) {
                System.out.println("第二种方式启动线程"+i);
            }
    
        }
    }
    
    
    
    
    
    public class test03 {
        public static void main(String[] args) throws ExecutionException, InterruptedException {
            MyCallable mc=new MyCallable();     //线程开启之后需要执行里面的call方法
            //可以获取线程执完毕之后的结果，也可以作为参数传递给Thread对象
            FutureTask<String> ft=new FutureTask<>(mc);
            Thread t=new Thread(ft);
            System.out.println(t.getName());
            t.start();
            String s = ft.get();
            System.out.println(s);
            MyCallable mc1=new MyCallable();     //线程开启之后需要执行里面的call方法
            //可以获取线程执完毕之后的结果，也可以作为参数传递给Thread对象
            FutureTask<String> ft1=new FutureTask<>(mc);
    //        Thread t1=new Thread(ft,"恒大大");
            Thread t1=new Thread(ft);
            t1.start();
            t1.setName("杨大大");
            System.out.println(t1.getName());
            String s1 = ft.get();
            System.out.println(s);
    
        }
    }
    
    public class MyCallable implements Callable<String> {
        @Override
        public String call() throws Exception {
            for (int i = 0; i < 100; i++) {
                System.out.println("第三种启动线程方式"+i);
                Thread.sleep(1000);
            }
            return "成功";
        }
    }

2.同步代码块、同步方法

![watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBAeWFuZzEzNTYzNzU4MTI4_size_17_color_FFFFFF_t_70_g_se_x_16][]

代码如下：

public class test04 {
        public static void main(String[] args) {
            MyRunnable1 mr=new MyRunnable1();
            Thread t=new Thread(mr);
            Thread t1=new Thread(mr);
            Thread t2=new Thread(mr);
            t.start();
            t1.start();
            t2.start();
        }
    
    }
    class MyRunnable1 implements Runnable{
        private int ticket=100;
        Object obj=new Object();
        @Override
        public void run() {
            while (true){
                synchronized (obj){         //同步代码块
                    if (ticket>0){
                        System.out.println(Thread.currentThread().getName()+"卖第"+ticket+"张票");
                        ticket--;
                    }
                    else {
                        return;
                    }
                }
            }
        }
    }

package com.xy;
    
    /**
     * @ProjectName: day01
     * @Package: com.xy
     * @ClassName: test04
     * @Author: 杨路恒
     * @Description:
     * @Date: 2021/8/26 0026 16:51
     * @Version: 1.0
     */
    public class test05 {
        public static void main(String[] args) {
            MyRunnable2 mr = new MyRunnable2();
            Thread t = new Thread(mr);
            Thread t1 = new Thread(mr);
            Thread t2 = new Thread(mr);
            t.start();
            t1.start();
            t2.start();
        }
    
    }
    
    class MyRunnable2 implements Runnable {
        private int ticket = 100;
        Object obj = new Object();
    
        @Override
        public void run() {
            while (true) {
                ticket();
            }
        }
    
        public synchronized void ticket() {
            if (ticket > 0) {
                System.out.println(Thread.currentThread().getName() + "卖第" + ticket + "张票");
                ticket--;
            } else {
                return;
            }
        }
    }

3.原子性、CAS算法

![watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBAeWFuZzEzNTYzNzU4MTI4_size_20_color_FFFFFF_t_70_g_se_x_16 2][]

![watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBAeWFuZzEzNTYzNzU4MTI4_size_20_color_FFFFFF_t_70_g_se_x_16 3][]

代码如下：

package com.xy;
    
    import java.util.concurrent.atomic.AtomicInteger;
    
    /**
     * @ProjectName: day01
     * @Package: com.xy
     * @ClassName: test16原子性
     * @Author: 杨路恒
     * @Description:
     * @Date: 2021/8/29 0029 14:08
     * @Version: 1.0
     */
    public class test16原子性 {
        public static void main(String[] args) {
            AtomicInteger ac=new AtomicInteger();
            System.out.println(ac);
            AtomicInteger ac1=new AtomicInteger(6);
            System.out.println(ac1);
        }
    }
    
    
    
    package com.xy;
    
    import java.util.concurrent.atomic.AtomicInteger;
    
    /**
     * @ProjectName: day01
     * @Package: com.xy
     * @ClassName: test17原子性
     * @Author: 杨路恒
     * @Description:
     * @Date: 2021/8/29 0029 14:10
     * @Version: 1.0
     */
    public class test17原子性 {
        public static void main(String[] args) {
            AtomicInteger ac=new AtomicInteger(6);
            System.out.println(ac.get());
            int i = ac.getAndIncrement();
            int i1 = ac.incrementAndGet();
            System.out.println(i);
            System.out.println(i1);
            int i2 = ac.addAndGet(6);
            System.out.println(i2);
            int i3 = ac.getAndSet(6);
            System.out.println(i);
        }
    }

4.线程池

![watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBAeWFuZzEzNTYzNzU4MTI4_size_20_color_FFFFFF_t_70_g_se_x_16 4][]

代码如下：

package com.xy;
    
    import java.util.concurrent.Executor;
    import java.util.concurrent.ExecutorService;
    import java.util.concurrent.Executors;
    
    /**
     * @ProjectName: day01
     * @Package: com.xy
     * @ClassName: test10线程池
     * @Author: 杨路恒
     * @Description:
     * @Date: 2021/8/27 0027 19:54
     * @Version: 1.0
     */
    public class test10线程池 {
        public static void main(String[] args) throws InterruptedException {
            ExecutorService executorService= Executors.newCachedThreadPool();
            executorService.submit(()->{
                System.out.println(Thread.currentThread().getName()+"启动");
            });
            Thread.sleep(2000);
            executorService.submit(()->{
                System.out.println(Thread.currentThread().getName()+"启动");
            });
            Thread.sleep(2000);
            executorService.shutdown(); 
        }
    }
    
    
    
    
    
    public class test13线程池 {
        public static void main(String[] args) {
            ThreadPoolExecutor pool=new ThreadPoolExecutor(2,
                    5,2,
                    TimeUnit.SECONDS,new ArrayBlockingQueue<>(10),
                    Executors.defaultThreadFactory(),new ThreadPoolExecutor.AbortPolicy());
            pool.submit(new MyRunnable3());
            pool.submit(new MyRunnable3());
            pool.shutdown();
        }
    }
    
    
    
    public class test14线程池 {
        public static void main(String[] args) {
            ThreadPoolExecutor pool=new ThreadPoolExecutor(1,
                    2,2,
                    TimeUnit.SECONDS,new ArrayBlockingQueue<>(1),
                    Executors.defaultThreadFactory(),
    //                new ThreadPoolExecutor.AbortPolicy());
    //                new ThreadPoolExecutor.DiscardPolicy());
    //                new ThreadPoolExecutor.DiscardOldestPolicy());
                    new ThreadPoolExecutor.CallerRunsPolicy());
            for (int i = 0; i < 5; i++) {
                int y=i;
                pool.submit(()->{
                    System.out.println(Thread.currentThread().getName()+":"+y);
                });
            }
            pool.shutdown();
        }
    }

5.阻塞队列

![watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBAeWFuZzEzNTYzNzU4MTI4_size_20_color_FFFFFF_t_70_g_se_x_16 5][]

代码如下：

public class test08阻塞队列 {
        public static void main(String[] args) {
            ArrayBlockingQueue<String> list=new ArrayBlockingQueue<>(1);
    
            Cooker1 c=new Cooker1(list);
            Foodie1 f=new Foodie1(list);
            c.start();
            f.start();
        }
    }
    
    
    
    public class test09阻塞队列 {
        public static void main(String[] args) throws InterruptedException {
            ArrayBlockingQueue<String> list=new ArrayBlockingQueue<>(1);
            list.put("汉堡包");
            System.out.println(list.take());
        }
    }
    
    
    
    public class Cooker1 extends Thread{
        ArrayBlockingQueue<String> list;
    
        public Cooker1(ArrayBlockingQueue<String> list) {
            this.list = list;
        }
    
        @Override
        public void run() {
            while (true){
                try {
                    list.put("汉堡包");
                    System.out.println("生产者");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }
    
    public class Foodie1 extends Thread{
        ArrayBlockingQueue<String> list;
    
        public Foodie1(ArrayBlockingQueue<String> list) {
            this.list = list;
        }
    
        @Override
        public void run() {
            while (true){
                try {
                    String take = list.take();
                    System.out.println("消费者");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }

生产者、消费者：

public class Cooker extends Thread {
        private Desk desk;
        public Cooker(Desk desk) {
    
        }
    
        @Override
        public void run() {
            while (true){
                synchronized (desk.getLock()){
                    if (desk.getCount()==0){
                        break;
                    }
                    else {
                        if (!desk.isFlag()){
                            System.out.println("生产者");
                            desk.setFlag(true);
                            desk.getLock().notifyAll();
                        }
                        else {
                            try {
                                desk.getLock().wait();
                            } catch (InterruptedException e) {
                                e.printStackTrace();
                            }
                        }
                    }
                }
            }
        }
    }
    
    
    
    public class Desk {
        private boolean flag=false;
        private int count=100;
        private final Object lock=new Object();
    
        public boolean isFlag() {
            return flag;
        }
    
        public void setFlag(boolean flag) {
            this.flag = flag;
        }
    
        public int getCount() {
            return count;
        }
    
        public void setCount(int count) {
            this.count = count;
        }
    
        public Object getLock() {
            return lock;
        }
    
        @Override
        public String toString() {
            return "Desk{" +
                    "flag=" + flag +
                    ", count=" + count +
                    ", lock=" + lock +
                    '}';
        }
    
        public Desk(boolean flag, int count) {
            this.flag = flag;
            this.count = count;
        }
    
        public Desk() {
            this(true,100);
        }
    }
    
    
    
    public class Foodie extends Thread{
    
        private Desk desk;
    
        public Foodie(Desk desk) {
    
        }
    
        @Override
        public void run() {
            while (true){
                synchronized (desk.getLock()){
                    if (desk.getCount()==0){
                        break;
                    }
                    else {
                        if (desk.isFlag()){
                            System.out.println("消费者");
                            desk.setFlag(false);
                            desk.getLock().notifyAll();
                            desk.setCount(desk.getCount()-1);
                        }
                        else {
                            try {
                                desk.getLock().wait();
                            } catch (InterruptedException e) {
                                e.printStackTrace();
                            }
                        }
                    }
                }
            }
        }
    }
    
    package com.xy;
    
    /**
     * @ProjectName: day01
     * @Package: com.xy
     * @ClassName: test07生产者消费者
     * @Author: 杨路恒
     * @Description:
     * @Date: 2021/8/27 0027 17:29
     * @Version: 1.0
     */
    public class test07生产者消费者 {
        public static void main(String[] args) {
            Desk desk=new Desk();
            Foodie f=new Foodie(desk);
            Cooker c=new Cooker(desk);
            f.start();
            c.start();
        }
    }

6.HashMap、HashTable、ConcurrentHashMap、CountDownLatch、

Semaphore

![watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBAeWFuZzEzNTYzNzU4MTI4_size_20_color_FFFFFF_t_70_g_se_x_16 6][]

代码如下：

package com.xy;
    
    import java.util.Hashtable;
    import java.util.concurrent.ConcurrentHashMap;
    
    /**
     * @ProjectName: day01
     * @Package: com.xy
     * @ClassName: test18并发工具类
     * @Author: 杨路恒
     * @Description:
     * @Date: 2021/8/29 0029 18:47
     * @Version: 1.0
     */
    public class test20ConcurrentMap {
        public static void main(String[] args) throws InterruptedException {
            ConcurrentHashMap<String,String> map=new ConcurrentHashMap<>();
            Thread t1=new Thread(()->{
                for (int i = 0; i < 25; i++) {
                    map.put(i+"",i+"");
                }
            });
            Thread t2=new Thread(()->{
                for (int i = 25; i < 51; i++) {
                    map.put(i+"",i+"");
                }
            });
            t1.start();
            t2.start();
            Thread.sleep(1000);
    
            for (int i = 0; i < 51; i++) {
                System.out.println(map.get(i+""));
            }
        }
    }
    
    
    
    
    package com.xy;
    
    import java.util.concurrent.CountDownLatch;
    
    /**
     * @ProjectName: day01
     * @Package: com.xy
     * @ClassName: test21CountDownLatch
     * @Author: 杨路恒
     * @Description:
     * @Date: 2021/8/30 0030 20:49
     * @Version: 1.0
     */
    public class test21CountDownLatch {
        public static void main(String[] args) {
            CountDownLatch countDownLatch=new CountDownLatch(3);
            MotherThread motherThread=new MotherThread(countDownLatch);
            motherThread.start();
            ChildThread1 t1=new ChildThread1(countDownLatch);
            t1.setName("杨大大");
            ChildThread2 t2=new ChildThread2(countDownLatch);
            t2.setName("恒大大");
            ChildThread3 t3=new ChildThread3(countDownLatch);
            t3.setName("路大大");
            t1.start();
            t2.start();
            t3.start();
        }
    }
    
    
    package com.xy;
    
    import java.util.concurrent.Semaphore;
    
    /**
     * @ProjectName: day01
     * @Package: com.xy
     * @ClassName: test22Semaphore
     * @Author: 杨路恒
     * @Description:
     * @Date: 2021/8/30 0030 21:07
     * @Version: 1.0
     */
    public class test22Semaphore {
        public static void main(String[] args) {
            SemaphoreRunnable sr=new SemaphoreRunnable();
            for (int i = 0; i < 100; i++) {
                new Thread(sr).start();
            }
        }
    }
    class SemaphoreRunnable implements Runnable{
        private Semaphore semaphore=new Semaphore(2);
        @Override
        public void run() {
            try {
                semaphore.acquire();
                System.out.println("获得了通行证开始行驶");
                Thread.sleep(2000);
                System.out.println("归还通行证");
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

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