10.線程池

什麼時線程池？

線程池是指在初始化一個多線程應用程序中建立的一個線程集合，而後在執行新的任務的時重用這些線程而不是從新建立一個線程，線程池中的線程數量徹底取決於可用內存數量和運用程序的需求，然而增長可用線程數是可能的，線程池中每個線程都有分配一個任務，一旦任務執行完後，會回到池子中並等待下一次的任務分配

 

 

1.建立一個可緩存線程池，若是線程池長度超過處理須要，可靈活回收空閒線程，若無可回收，則新建線程。

//最經常使用的線程池

package com.jlong;

 

import java.util.concurrent.ExecutorService;

import java.util.concurrent.Executors;

 

public class NewCachedThreadTest {

    public static void main(String[] args) {

        //建立可緩存線程

        ExecutorService executorService = Executors.newCachedThreadPool();

        //執行execute表示建立了線程 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.建立一個定長線程池，可控制線程最大併發數，超出的線程會在隊列中等待。

 

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.建立一個定長線程池，支持定時及週期性任務執行。延遲執行

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("三秒鐘後執行。。。。。");

            }

        },3, TimeUnit.SECONDS);

 

    }

}

 

4.單線程，幾乎沒有用到

 

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);

                }

            });

        }

    }

}