[Java知识库](Java) 线程池

线程池：
    1.出现版本：JDK1.5
    2.包：java.util.concurrent
    3.Executors类 -->工厂类
        1.三个静态方法：
        static ExecutorService newCachedThreadPool()  创建新的线程池对象
        Creates a thread pool that creates new threads as needed, but will reuse previously constructed threads when they are available.
        static ExecutorService newFixedThreadPool(int nThreads)  创建目标个数的线程池
        Creates a thread pool that reuses a fixed number of threads operating off a shared unbounded queue.
        tatic ExecutorService  newSingleThreadExecutor() 创建一个线程
        Creates an Executor that uses a single worker thread operating off an unbounded queue.


        2.ExecutorService 是一个接口

        <T> Future<T>  submit(Callable<T> task)
        Submits a value-returning task for execution and returns a Future representing the pending results of the task.
        Future<?>  submit(Runnable task)
        Submits a Runnable task for execution and returns a Future representing that task.

        3.Future 是运行后的结果
          Callable是一个接口，call（）方法有返回值
          public interface Callable<V>

    4.实现线程的三种方式：
     1.继承Thead 类
     2.实现Runnable 接口
     3.实现 Callable 接口-----只要线程池支持，Thead不支持
     

//第一个class文件
public class RunnablePoolDemo implements Runnable{
    public void run(){
        for(int x =0;x<20;x++){
            System.out.println(Thread.currentThread().getName()+"run.."+x);
        }
    }
}




//第二个class文件
import java.util.concurrent.Callable;

/**
 * @author Alina
 * @date 2021年12月25日 11:59 下午
 */
public class CallableSumDemo implements Callable<Integer> {
    private Integer num = 0;
    public CallableSumDemo(Integer num) {
        this.num = num;
    }

    public Integer call() {
        int sum  = 0;
        for (int x = 0;x<=num;x++){
            sum = sum +x;
        }
        return sum;
    }
}




//主文件

package thread;


import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

/**
 * @author Alina
 * @date 2021年12月25日 11:17 下午
 * 创建线程池
 *  实现方法：
 *  1.创建 Executors 类，静态调用，创建两个线程池
 *  3.返回对象：ExecutorService
 *
 */
public class TheadPoolDemo {
    public static void main(String[] args) throws Exception{
        method_3();



    }
    public static void method_3 () throws ExecutionException, InterruptedException {
        ExecutorService es3 = Executors.newFixedThreadPool(2);
        Future<Integer> f1 = es3.submit(new CallableSumDemo(100));
        Future<Integer> f2 = es3.submit(new CallableSumDemo(200));
        int sum1 = f1.get();
        int sum2 = f2.get();

        System.out.println(sum1);
        System.out.println(sum2);
        es3.shutdown();
    }
    public static void method_2() throws Exception{
       ExecutorService es2 = Executors.newFixedThreadPool(2);
       Future<String> ft = es2.submit(new CallablePoolDemo());
       String name = ft.get();
       System.out.println(name);

    }
    public static void method_1(){
        ExecutorService es = Executors.newFixedThreadPool(2);
        es.submit(new RunnablePoolDemo());
        es.submit(new RunnablePoolDemo());
        es.shutdown();
    }
}