10.线程池

什么时线程池？

线程池是指在初始化一个多线程应用程序中建立的一个线程集合，而后在执行新的任务的时重用这些线程而不是从新建立一个线程，线程池中的线程数量彻底取决于可用内存数量和运用程序的需求，然而增长可用线程数是可能的，线程池中每个线程都有分配一个任务，一旦任务执行完后，会回到池子中并等待下一次的任务分配

 

 

1.建立一个可缓存线程池，若是线程池长度超过处理须要，可灵活回收空闲线程，若无可回收，则新建线程。

//最经常使用的线程池

package com.jlong;

 

import java.util.concurrent.ExecutorService;

import java.util.concurrent.Executors;

 

public class NewCachedThreadTest {

    public static void main(String[] args) {

        //建立可缓存线程

        ExecutorService executorService = Executors.newCachedThreadPool();

        //执行execute表示建立了线程 相似start()

        for (int i = 0; i <30 ; i++) {

            int index=i;

            executorService.execute(new Runnable() {

                @Override

                public void run() {

                    System.out.println(Thread.currentThread()+"----"+index);

                }

            });

        }

    }

}

 

2.建立一个定长线程池，可控制线程最大并发数，超出的线程会在队列中等待。

 

package com.jlong;

 

import java.util.concurrent.ExecutorService;

import java.util.concurrent.Executors;

 

public class NewFiexdThreadPoolTest {

    public static void main(String[] args) {

        ExecutorService executorService = Executors.newFixedThreadPool(3);

        for (int i = 0; i <30 ; i++) {

            int index=i;

            executorService.execute(new Runnable() {

                @Override

                public void run() {

 

                    try {

                        Thread.sleep(500);

                        System.out.println(Thread.currentThread()+"----"+index);

                    } catch (Exception e) {

                        e.printStackTrace();

                    }

                }

            });

        }

    }

}

3.建立一个定长线程池，支持定时及周期性任务执行。延迟执行

package com.jlong;

 

import java.util.concurrent.Executors;

import java.util.concurrent.ScheduledExecutorService;

import java.util.concurrent.TimeUnit;

 

public class NewScheduledThreadTest {

    public static void main(String[] args) {

        ScheduledExecutorService scheduledExecutorService = Executors.newScheduledThreadPool(6);

        scheduledExecutorService.schedule(new Runnable() {

            @Override

            public void run() {

                System.out.println("三秒钟后执行。。。。。");

            }

        },3, TimeUnit.SECONDS);

 

    }

}

 

4.单线程，几乎没有用到

 

package com.jlong;

 

import java.util.concurrent.ExecutorService;

import java.util.concurrent.Executors;

 

public class NewSingleThreadExecutorTest {

    public static void main(String[] args) {

        ExecutorService executorService = Executors.newSingleThreadExecutor();

        for (int i = 0; i < 30; i++) {

            int index=i;

            executorService.execute(new Runnable() {

                @Override

                public void run() {

                    System.out.println(Thread.currentThread().getName()+"------"+index);

                }

            });

        }

    }

}