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我们都知道线程池高效，是因为其节省了线程创建的资源。

那么到底是怎样节省的呢？其实也很简单，就是根据给的知道线程池大小去new 多少个 Thread ，然后在 run 方法里面无限循环，从线程池的 任务队列里面获取方法执行。

代码实例：

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.TimeUnit;/*** 自定义固定大小的线程池*/
public class FixedSizeThreadPool {/*** 装所有任务*/private ArrayBlockingQueue<Runnable> queue;/*** 装所有线程*/private List<Thread> workes;// 线程名private String tname;public FixedSizeThreadPool(int poolSize , int taskSize , String tname){if(poolSize<0 || taskSize<0){throw new IllegalArgumentException("非法的参数");}// 实例化无界队列，用于装任务this.queue = new ArrayBlockingQueue<>(taskSize);this.workes = Collections.synchronizedList(new ArrayList<>());for (int i = 0; i < poolSize; i++) {Worker worker = new Worker(this);worker.setThreadName(tname + "===>" + i);worker.start();this.workes.add(worker);}}/*** 开几个线程执行，最大执行多少个任务* @param poolSize* @param taskSize*/public FixedSizeThreadPool(int poolSize , int taskSize){this(poolSize , taskSize , "Thread");}/*** 提交任务* @param task* @return*/public boolean submit(Runnable task){return this.queue.offer(task);}/*** 关闭线程池*/public void shutdown(){// 当任务队列里面的数据为空的时候，则证明任务都执行完毕了(或者已经开始执行了)，就可以进行下一步关闭线程了while (this.queue.size()!=0){}for (int i = 0; i < this.workes.size(); i++) {((Worker) this.workes.get(i)).setFlag(false);}}public static class Worker extends Thread{private boolean flag;public void setFlag(boolean flag) {this.flag = flag;}// 固定线程池对象，从里面拿出 任务来执行private FixedSizeThreadPool pool;public Worker(FixedSizeThreadPool pool){this.flag = true;this.pool = pool;}public void setThreadName(String tname){super.setName(tname);}// 不断循环，从队列中拿到任务来执行@Overridepublic void run() {while (flag){Runnable task = null;try {task = this.pool.queue.poll(10,TimeUnit.SECONDS);} catch (InterruptedException e) {e.printStackTrace();}if (task != null) {task.run();System.out.println("线程" + Thread.currentThread().getName() + "执行了..." );}}System.out.println("线程死亡！！！");}}public static void main(String[] args) {FixedSizeThreadPool pool = new FixedSizeThreadPool(3, 6);for (int i = 0; i < 6; i++) {final int index = i;pool.submit(new Runnable() {@Overridepublic void run() {System.err.println("start exec task " + index);}});}try {Thread.sleep(1000);} catch (InterruptedException e) {e.printStackTrace();}for (int i = 10; i < 16; i++) {final int index = i;pool.submit(new Runnable() {@Overridepublic void run() {System.err.println("start exec task " + index);}});}pool.shutdown();}}