第45天学习打卡（Set 不安全 Map不安全 Callable 常用的辅助类 读写锁 阻塞队列 线程池）

Set不安全

package com.kuang.unsafe;

import java.util.*;
import java.util.concurrent.CopyOnWriteArraySet;

/**
 * 同理可证：ConcurrentModificationException并发修改异常
 * 解决方法：
 * //1.Set<String> set = Collections.synchronizedSet(new HashSet<>());工具类的写法
 * //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 = 1; i <= 30; i++) {
    
    
            new Thread(()->{
    
    
                set.add(UUID.randomUUID().toString().substring(0,5));
                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是常量固定的值 不会变
 private static final Object PRESENT = new Object();

Map不安全

回顾map的基本操作

package com.kuang.unsafe;

import java.util.HashMap;
import java.util.Map;
import java.util.UUID;
import java.util.concurrent.ConcurrentHashMap;

//ConcurrentModificationException 并发修改异常
public class MapTest {
    
    
    public static void main(String[] args) {
    
    
        //map是这样用的吗？   不是 工作中不用HashMap
        //默认等价于什么？？ new HashMap<>(16,0.75);
        //HashMap<String, String> map = new HashMap<>();
        Map<String,String> map = new ConcurrentHashMap<>();
        for (int i = 1; i < 30; i++) {
    
    
            new Thread(()->{
    
    
                map.put(Thread.currentThread().getName(), UUID.randomUUID().toString().substring(0,5));
                System.out.println(map);

            },String.valueOf(i)).start();
            
        }

        //加载因子  初始化容量
    }
}

7.Callable

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.kuang.callable;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.FutureTask;
import java.util.concurrent.locks.ReentrantLock;
public class CallableTest {
    
    
    public static void main(String[] args) throws ExecutionException, InterruptedException {
    
    
       //new Thread(new Runnable()).start();//Runnable()) 和FutureTask<V>()两者等价
       //new Thread(new FutureTask<V>(Callable)).start();//FutureTask可以调用(Callable)
        //new Thread().start()是可以启动Callable
        new Thread().start();//怎么启动Callable
        MyThread thread = new MyThread();
        FutureTask<Integer> futureTask = new FutureTask<>(thread);//适配类

        new Thread(futureTask,"A").start();
        Integer o = (Integer) futureTask.get();//获取Callable返回结果
        System.out.println(o);


    }
}
class MyThread implements Callable<Integer> {
    
    
    @Override

    public Integer call(){
    
    
        System.out.println("call()");
        return 1024;

    }
}

package com.kuang.callable;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.FutureTask;
import java.util.concurrent.locks.ReentrantLock;
public class CallableTest {
    
    
    public static void main(String[] args) throws ExecutionException, InterruptedException {
    
    
       //new Thread(new Runnable()).start();//Runnable()) 和FutureTask<V>()两者等价
       //new Thread(new FutureTask<V>(Callable)).start();//FutureTask可以调用(Callable)
        //new Thread().start()是可以启动Callable
        new Thread().start();//怎么启动Callable
        MyThread thread = new MyThread();
        FutureTask<Integer> futureTask = new FutureTask<>(thread);//适配类

        new Thread(futureTask,"A").start();//A为线程
        new Thread(futureTask,"B").start();//B为线程   打印的结果只有一个call 因为结果会被缓存，效率高
        Integer o = (Integer) futureTask.get();//获取Callable返回结果
        //这个get方法可能会产生阻塞，把它放在最后
        //或者使用异步通信来处理
        System.out.println(o);


    }
}
class MyThread implements Callable<Integer> {
    
    
    @Override

    public Integer call(){
    
    
        System.out.println("call()");
        return 1024;

    }
}

细节：

​ 1.缓存

​ 2.结果可能需要等待，会阻塞！

8 常用的辅助类（必会）

8.1 CountDownLatch

package com.kuang.add;

import java.util.concurrent.CountDownLatch;

//计数器
public class CountDownLatchDemo {
    
    
    public static void main(String[] args) throws InterruptedException {
    
    
        //总数是6的倒计时， 必须要执行任务的时候，再使用
        CountDownLatch countDownLatch = new CountDownLatch(6);
        for (int i = 1; i <= 6; i++) {
    
    
            new Thread(()->{
    
    
                System.out.println(Thread.currentThread().getName()+"Go out");
                countDownLatch.countDown();//数量减一

            },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");


    }
}

减法计数器

原理：

1. countDownLatch.countDown();//数量减一

2. countDownLatch.await();//等待计数器归零，然后再向下执行

   每次有线程调用countDown()数量减一。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

package com.kuang.add;

import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;

public class CyclicBarrierDemo {
    
    
    public static void main(String[] args) {
    
    
        /**
         * 集齐7颗龙珠召唤神龙
         */
        //召唤龙珠的线程
        CyclicBarrier cyclicBarrier = new CyclicBarrier(7,()->{
    
    
            System.out.println("召唤神龙成功!");

        });


        for (int i = 1; i <=7; i++) {
    
    
            final int temp = i;

            //lambda能操作到i吗？
            new Thread(()->{
    
    
                System.out.println(Thread.currentThread().getName()+"搜集"+temp+"个龙珠");
                try {
    
    
                    cyclicBarrier.await();//等待7个线程结束
                } catch (InterruptedException e) {
    
    
                    e.printStackTrace();
                } catch (BrokenBarrierException e) {
    
    
                    e.printStackTrace();
                }


            }).start();

        }
    }
}

8.3 Semaphore

package com.kuang.add;

import java.util.concurrent.Semaphore;
import java.util.concurrent.TimeUnit;

public class SemaphoreDemo {
    
    
    public static void main(String[] args) {
    
    
        //线程数量： 类比于停车位 3个停车位 限流的时候可以用
        Semaphore semaphore = new Semaphore(3);
        for (int i = 1; i <=6 ; i++) {
    
    
            new Thread(()->{
    
    
                //acquire() 得到
                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 {
    
    
                    //release() 释放
                  semaphore.release();
                }


            },String.valueOf(i)).start();
            
        }
    }
}

原理：

semaphore.acquire();//获取,假设已经满了，等待，等待释放为止！

semaphore.release();//释放，会将当前的信号量释放+1，然后唤醒等待的线程！

作用：多个共享资源互斥使用！并发限流，控制最大的线程数。

9读写锁

ReadWriteLock

package com.kuang.rw;


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;

/**
 * 独占锁（写锁）一次只能被一个线程占有
 * 共享锁（读锁） 多个线程可以同时占有
 * ReadWriteLockDemo
 * 读-读 可以共存
 * 读-写 不能共存
 * 写-写 不能共存
 */
public class ReadWriteLockDemo {
    
    
    public static void main(String[] args) {
    
    
        MyCacheLock myCache = new MyCacheLock();

        //写入 lambda表达式无法访问外部变量，只有通过fianl变量去进行中间转换
        for (int i = 1; i <= 5; i++) {
    
    
            final int temp = i;
            new Thread(()->{
    
    
                myCache.put(temp+"",temp+"");
            },String.valueOf(i)).start();
            
        }
        //读取
        for (int i = 1; i <= 5; i++) {
    
    
            final int temp = i;
            new Thread(()->{
    
    
                myCache.get(temp+"");
            },String.valueOf(i)).start();

        }

       
    }
}
class MyCacheLock{
    
    
    private volatile Map<String,Object> map = new HashMap<>();
    //读写锁，更加细粒度的控制
    private ReadWriteLock readWriteLock =  new ReentrantReadWriteLock();
    //存，写的过程 只希望同时只有一个线程写
    public void put(String key,Object value){
    
    
        readWriteLock.writeLock().lock();

        try {
    
    
            System.out.println(Thread.currentThread().getName()+"写入"+key);
            map.put(key, value);
            System.out.println(Thread.currentThread().getName()+"写入OK");

        } catch (Exception e) {
    
    
            e.printStackTrace();
        } finally {
    
    
            readWriteLock.writeLock().unlock();
        }

    }
    //取，读的过程 所有人都可以去读
    public void get(String key){
    
    
        readWriteLock.readLock().lock();

        try {
    
    
            System.out.println(Thread.currentThread().getName()+"读取"+key);
            Object o = map.get(key);
            System.out.println(Thread.currentThread().getName()+"读取OK");
        } catch (Exception e) {
    
    
            e.printStackTrace();
        } finally {
    
    
            readWriteLock.readLock().unlock();
        }



    }


}
/**
 * 自定义缓存
 */
 class MyCache{
    
    
     private volatile Map<String,Object> map = new HashMap<>();
     //存，写的过程

     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，读的过程
    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");


    }


}

10 阻塞队列

队列 ：FIFO

写入：如果队列满了，就必须阻塞等待

取：如果队列是空的，必须阻塞等待生产

不得不阻塞

阻塞队列：

BlockingQueue： 不是新的东西

什么情况下我们会使用阻塞队列：多线程并发处理，线程池！

学会使用队列

添加 移除

四组API

方式	抛出异常	有返回值,不抛出异常	阻塞等待	超时等待
添加	add	offer()空参	put()	offer(,)
移除	remove	pool()	take()	poll(,)
检测队首元素	element	peek()	-	-

package com.kuang.bq;

import java.util.concurrent.ArrayBlockingQueue;

public class Test {
    
    
    public static void main(String[] args) {
    
    
        test1();

    }
    /**
     * 抛出异常
     */
    public static void test1(){
    
    
        //<>（）放队列的大小
        ArrayBlockingQueue blockingQueue = new ArrayBlockingQueue<>(3);

        System.out.println(blockingQueue.add("a"));
        System.out.println(blockingQueue.add("b"));
        System.out.println(blockingQueue.add("c"));
        System.out.println("++++++++++++++++++++++++++++");


        //IllegalStateException: Queue full抛出异常
       // System.out.println(blockingQueue.add("d"));
        System.out.println(blockingQueue.remove());
        System.out.println(blockingQueue.remove());
        System.out.println(blockingQueue.remove());

        //java.util.NoSuchElementException没有元素错误 抛出异常
        System.out.println(blockingQueue.remove());

    }
}

package com.kuang.bq;

import java.util.concurrent.ArrayBlockingQueue;

public class Test {
    
    
    public static void main(String[] args) {
    
    
        test2();

    }
    /**
     * 抛出异常
     */
    public static void test1(){
    
    
        //<>（）放队列的大小
        ArrayBlockingQueue blockingQueue = new ArrayBlockingQueue<>(3);

        System.out.println(blockingQueue.add("a"));
        System.out.println(blockingQueue.add("b"));
        System.out.println(blockingQueue.add("c"));
        System.out.println("++++++++++++++++++++++++++++");


        //IllegalStateException: Queue full抛出异常
       // System.out.println(blockingQueue.add("d"));
        System.out.println(blockingQueue.remove());
        System.out.println(blockingQueue.remove());
        System.out.println(blockingQueue.remove());

        //java.util.NoSuchElementException没有元素错误 抛出异常
        System.out.println(blockingQueue.remove());

    }

    /**
     * 有返回值，没有异常
     */
    public static void test2() {
    
    
        //队列的大小
    ArrayBlockingQueue blockingQueue = new ArrayBlockingQueue<>(3);
     //存
    System.out.println(blockingQueue.offer("a"));
    System.out.println(blockingQueue.offer("b"));
    System.out.println(blockingQueue.offer("c"));

    System.out.println(blockingQueue.offer("d"));//返回false 不抛出异常
    //取
    System.out.println("===============================");
    System.out.println(blockingQueue.poll());
    System.out.println(blockingQueue.poll());
    System.out.println(blockingQueue.poll());

    System.out.println(blockingQueue.poll());//返回值为null,也不抛出异常



}
}

输出结果：

true
true
true

false

a
b
c
null

Process finished with exit code 0

查看队首元素 System.out.println(blockingQueue.element())放在哪个remove 前面，哪个就是队首 其余的元素就被移除了

package com.kuang.bq;

import java.util.concurrent.ArrayBlockingQueue;

public class Test {
    
    
    public static void main(String[] args) {
    
    
        test1();

    }
    /**
     * 抛出异常
     */
    public static void test1(){
    
    
        //<>（）放队列的大小
        ArrayBlockingQueue blockingQueue = new ArrayBlockingQueue<>(3);

        System.out.println(blockingQueue.add("a"));
        System.out.println(blockingQueue.add("b"));
        System.out.println(blockingQueue.add("c"));


        System.out.println("++++++++++++++++++++++++++++");


        //IllegalStateException: Queue full抛出异常
       // System.out.println(blockingQueue.add("d"));
       // System.out.println(blockingQueue.remove());
        System.out.println(blockingQueue.remove());

     
        System.out.println(blockingQueue.remove());
        System.out.println(blockingQueue.element());//查看队首元素
        System.out.println(blockingQueue.remove());

        //java.util.NoSuchElementException没有元素错误 抛出异常
        //System.out.println(blockingQueue.remove());

    }

    /**
     * 有返回值，没有异常
     */
    public static void test2() {
    
    
        //队列的大小
    ArrayBlockingQueue blockingQueue = new ArrayBlockingQueue<>(3);
     //存
    System.out.println(blockingQueue.offer("a"));
    System.out.println(blockingQueue.offer("b"));
    System.out.println(blockingQueue.offer("c"));

    System.out.println(blockingQueue.offer("d"));//返回false 不抛出异常
    //取
    System.out.println("===============================");
    System.out.println(blockingQueue.poll());
    System.out.println(blockingQueue.poll());
    System.out.println(blockingQueue.poll());

    System.out.println(blockingQueue.poll());//返回值为null,也不抛出异常



}
}

package com.kuang.bq;

import java.util.concurrent.ArrayBlockingQueue;

public class Test {
    
    
    public static void main(String[] args) {
    
    
        test2();

    }
    /**
     * 抛出异常
     */
    public static void test1(){
    
    
        //<>（）放队列的大小
        ArrayBlockingQueue blockingQueue = new ArrayBlockingQueue<>(3);

        System.out.println(blockingQueue.add("a"));
        System.out.println(blockingQueue.add("b"));
        System.out.println(blockingQueue.add("c"));


        System.out.println("++++++++++++++++++++++++++++");


        //IllegalStateException: Queue full抛出异常
       // System.out.println(blockingQueue.add("d"));
       // System.out.println(blockingQueue.remove());
        System.out.println(blockingQueue.remove());


        System.out.println(blockingQueue.remove());
        System.out.println(blockingQueue.element());//查看队首元素
        System.out.println(blockingQueue.remove());

        //java.util.NoSuchElementException没有元素错误 抛出异常
        //System.out.println(blockingQueue.remove());

    }

    /**
     * 有返回值，没有异常
     */
    public static void test2() {
    
    
        //队列的大小
    ArrayBlockingQueue blockingQueue = new ArrayBlockingQueue<>(3);
     //存
    System.out.println(blockingQueue.offer("a"));
    System.out.println(blockingQueue.offer("b"));
    System.out.println(blockingQueue.offer("c"));

        System.out.println(blockingQueue.peek());

       // System.out.println(blockingQueue.offer("d"));//返回false 不抛出异常
    //取
    System.out.println("===============================");
    System.out.println(blockingQueue.poll());
    System.out.println(blockingQueue.poll());
    System.out.println(blockingQueue.poll());

  //  System.out.println(blockingQueue.poll());//返回值为null,也不抛出异常



}
}

package com.kuang.bq;

import java.util.concurrent.ArrayBlockingQueue;

public class Test {
    
    
    public static void main(String[] args) throws InterruptedException {
    
    
        test3();

    }
    /**
     * 抛出异常
     */
    public static void test1(){
    
    
        //<>（）放队列的大小
        ArrayBlockingQueue blockingQueue = new ArrayBlockingQueue<>(3);

        System.out.println(blockingQueue.add("a"));
        System.out.println(blockingQueue.add("b"));
        System.out.println(blockingQueue.add("c"));


        System.out.println("++++++++++++++++++++++++++++");


        //IllegalStateException: Queue full抛出异常
       // System.out.println(blockingQueue.add("d"));
       // System.out.println(blockingQueue.remove());
        System.out.println(blockingQueue.remove());


        System.out.println(blockingQueue.remove());
        System.out.println(blockingQueue.element());//查看队首元素
        System.out.println(blockingQueue.remove());

        //java.util.NoSuchElementException没有元素错误 抛出异常
        //System.out.println(blockingQueue.remove());

    }

    /**
     * 有返回值，没有异常
     */
    public static void test2() {
    
    
        //队列的大小
    ArrayBlockingQueue blockingQueue = new ArrayBlockingQueue<>(3);
     //存
    System.out.println(blockingQueue.offer("a"));
    System.out.println(blockingQueue.offer("b"));
    System.out.println(blockingQueue.offer("c"));

        System.out.println(blockingQueue.peek());

       // System.out.println(blockingQueue.offer("d"));//返回false 不抛出异常
    //取
    System.out.println("===============================");
    System.out.println(blockingQueue.poll());
    System.out.println(blockingQueue.poll());
    System.out.println(blockingQueue.poll());

  //  System.out.println(blockingQueue.poll());//返回值为null,也不抛出异常



}
/**
 * 等待，阻塞（一直阻塞）
 */
public static void test3() throws InterruptedException {
    
    
    //队列的大小
    ArrayBlockingQueue blockingQueue = new ArrayBlockingQueue<>(3);

    //一直阻塞
    //存
    blockingQueue.put("a");
    blockingQueue.put("b");
    blockingQueue.put("c");
   // blockingQueue.put("d");//队列没有位置了会一直等待

    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，会一直阻塞


}

/**
 * 等待，阻塞（等待超时）
 */
}

package com.kuang.bq;

import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.TimeUnit;

public class Test {
    
    
    public static void main(String[] args) throws InterruptedException {
    
    
        test4();

    }
    /**
     * 抛出异常
     */
    public static void test1(){
    
    
        //<>（）放队列的大小
        ArrayBlockingQueue blockingQueue = new ArrayBlockingQueue<>(3);

        System.out.println(blockingQueue.add("a"));
        System.out.println(blockingQueue.add("b"));
        System.out.println(blockingQueue.add("c"));


        System.out.println("++++++++++++++++++++++++++++");


        //IllegalStateException: Queue full抛出异常
       // System.out.println(blockingQueue.add("d"));
       // System.out.println(blockingQueue.remove());
        System.out.println(blockingQueue.remove());


        System.out.println(blockingQueue.remove());
        System.out.println(blockingQueue.element());//查看队首元素
        System.out.println(blockingQueue.remove());

        //java.util.NoSuchElementException没有元素错误 抛出异常
        //System.out.println(blockingQueue.remove());

    }

    /**
     * 有返回值，没有异常
     */
    public static void test2() {
    
    
        //队列的大小
    ArrayBlockingQueue blockingQueue = new ArrayBlockingQueue<>(3);
     //存
    System.out.println(blockingQueue.offer("a"));
    System.out.println(blockingQueue.offer("b"));
    System.out.println(blockingQueue.offer("c"));

        System.out.println(blockingQueue.peek());

       // System.out.println(blockingQueue.offer("d"));//返回false 不抛出异常
    //取
    System.out.println("===============================");
    System.out.println(blockingQueue.poll());
    System.out.println(blockingQueue.poll());
    System.out.println(blockingQueue.poll());

  //  System.out.println(blockingQueue.poll());//返回值为null,也不抛出异常



}
/**
 * 等待，阻塞（一直阻塞）
 */
public static void test3() throws InterruptedException {
    
    
    //队列的大小
    ArrayBlockingQueue blockingQueue = new ArrayBlockingQueue<>(3);

    //一直阻塞
    //存
    blockingQueue.put("a");
    blockingQueue.put("b");
    blockingQueue.put("c");
   // blockingQueue.put("d");//队列没有位置了会一直等待

    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，会一直阻塞


}

/**
 * 等待，阻塞（等待超时）
 */
public static void test4() throws InterruptedException {
    
    
    //队列的大小
    ArrayBlockingQueue blockingQueue = new ArrayBlockingQueue<>(3);
    //存

    blockingQueue.offer("a");
    blockingQueue.offer("b");
    blockingQueue.offer("c");
    //blockingQueue.offer("d",2, TimeUnit.SECONDS);//延迟两秒，超时退出

    System.out.println("===========================");
    System.out.println(blockingQueue.poll());
    System.out.println(blockingQueue.poll());
    System.out.println(blockingQueue.poll());
    blockingQueue.poll(2, TimeUnit.SECONDS);//等待超过2秒就退出



}
}

SynchronousQueue同步队列

没有容量

进去一个元素，必须等待取出来之后，才能往里面放一个元素

put take

package com.kuang.bq;

import java.util.concurrent.BlockingQueue;
import java.util.concurrent.SynchronousQueue;
import java.util.concurrent.TimeUnit;

/**
 * 同步队列
 * 和其他的BlockingQueue不一样，SynchronousQueue不存储元素
 * put了一个元素，必须从里面先take取出来，否则不能在put进去值
 */
public class SynchronousQueueDemo {
    
    
    public static void main(String[] args) {
    
    
        BlockingQueue<String> blockingQueue  = new SynchronousQueue<>();//同步队列

        new Thread(()->{
    
    

            try {
    
    
                System.out.println(Thread.currentThread().getName()+"put 1");
                blockingQueue.put("1");
                System.out.println(Thread.currentThread().getName()+"put 2");
                blockingQueue.put("2");
                System.out.println(Thread.currentThread().getName()+"put 3");
                blockingQueue.put("3");
            } catch (InterruptedException e) {
    
    
                e.printStackTrace();
            }

        },"T1").start();
        new Thread(()->{
    
    
            try {
    
    
                TimeUnit.SECONDS.sleep(3);
                System.out.println(Thread.currentThread().getName()+"=>"+blockingQueue.take());
                TimeUnit.SECONDS.sleep(3);
                System.out.println(Thread.currentThread().getName()+"=>"+blockingQueue.take());
                TimeUnit.SECONDS.sleep(3);
                System.out.println(Thread.currentThread().getName()+"=>"+blockingQueue.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

池化技术

程序的运行，本质：占用系统的资源！优化资源的使用！=>池化技术

线程池、连接池、内存池、对象池///… 创建、销毁，十分浪费资源

池化技术：事先准备好一些资源，有人要用，就来我这里拿，用完之后还给我。

线程池的好处：

1.降低资源的消耗

2.提高响应的速度

3.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：三大方法

package com.kuang.pool;

import java.util.concurrent.Executor;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
// Executors工具类 三大方法
//使用了线程池之后，使用线程池来创建线程
public class Demo01 {
    
    
    public static void main(String[] args) {
    
    
       ExecutorService threadPool = Executors.newSingleThreadExecutor();//单个线程
       //ExecutorService threadPool = Executors.newFixedThreadPool(5);//创建一个固定的线程池的大小
        //ExecutorService threadPool =  Executors.newCachedThreadPool();//缓存的  可以伸缩，遇强则强，遇弱则弱


        try {
    
    
            for (int i = 0; i < 100 ; i++) {
    
    
                //使用了线程池之后，使用线程池来创建线程
                threadPool.execute(()->{
    
    
                    System.out.println(Thread.currentThread().getName()+" ok");

                });

            }

        } catch (Exception e) {
    
    
            e.printStackTrace();
        } finally {
    
    
            //线程池用完，程序结束，关闭线程池
            threadPool.shutdown();
        }
    }
}

7大参数

源码分析：

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,//约为21亿
                                      60L, TimeUnit.SECONDS,
                                      new SynchronousQueue<Runnable>());
    }


本质： ThreadPoolExecutor

public ThreadPoolExecutor(int corePoolSize,//核心线程池大小
                              int maximumPoolSize,//最大的线程池大小
                              long keepAliveTime,//超时了，没有人调用就会释放
                              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;
    }

手动创建一个线程池

四种拒绝策略

package com.kuang.pool;

import java.util.concurrent.*;

// Executors工具类 三大方法

/**
 * new ThreadPoolExecutor.AbortPolicy());//银行满了，还有人进来，不处理这个人的，抛出异常
 * new ThreadPoolExecutor.CallerRunsPolicy());//哪来的去哪里
 *  new ThreadPoolExecutor.DiscardPolicy());//队列满了，丢掉任务，不会抛出异常
 *  new ThreadPoolExecutor.DiscardOldestPolicy());//队列满了，尝试去和最早的竞争，也不会抛出异常
 */
//使用了线程池之后，使用线程池来创建线程
public class Demo01 {
    
    
    public static void main(String[] args) {
    
    
        //自定义线程池！工作中使用ThreadPoolExecutor
        //假设核心线程池有2个 就是2个银行业务员，最大同时有5个人去办理 超过3秒就不等了 LinkedBlockingDeque<>()侯客区只能放3人

      ExecutorService threadPool = new ThreadPoolExecutor(2,
              5,
              3,
              TimeUnit.SECONDS,
              new LinkedBlockingDeque<>(3),
      Executors.defaultThreadFactory(),
              new ThreadPoolExecutor.DiscardOldestPolicy());//队列满了，尝试去和最早的竞争，也不会抛出异常

        try {
    
    
            //最大承载：Deque + max
            //RejectedExecutionException超出最大承载抛出的异常
            for (int i = 1; i <= 9 ; i++) {
    
    
                //使用了线程池之后，使用线程池来创建线程
                threadPool.execute(()->{
    
    
                    System.out.println(Thread.currentThread().getName()+" ok");

                });

            }

        } catch (Exception e) {
    
    
            e.printStackTrace();
        } finally {
    
    
            //线程池用完，程序结束，关闭线程池
            threadPool.shutdown();
        }
    }
}