新的线程加入后，如果正在运行的线程达到了上限，则会阻塞，直到有了空闲的线程来运行。
import java.util.Random;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

/**
* 线程池newFixedThreadPool的使用。
*
* @author 赵学庆，Java世纪网(java2000.net)
*
*/
public class ExecutorTest {
public static void main(String args[]) {
Random random = new Random();
// 建立一个容量为3的固定尺寸的线程池
ExecutorService executor = Executors.newFixedThreadPool(3);
// 判断可是线程池可以结束
int waitTime = 500;
for (int i = 0; i < 10; i++) {
String name = "线程 " + i;
int time = random.nextInt(1000);
waitTime += time;
Runnable runner = new ExecutorThread(name, time);
System.out.println("增加: " + name + " / " + time);
executor.execute(runner);
}
try {
Thread.sleep(waitTime);
executor.shutdown();
executor.awaitTermination(waitTime, TimeUnit.MILLISECONDS);
} catch (InterruptedException ignored) {
}
}
}

class ExecutorThread implements Runnable {
private final String name;
private final int delay;

public ExecutorThread(String name, int delay) {
this.name = name;
this.delay = delay;
}

public void run() {

System.out.println("启动: " + name);
try {
Thread.sleep(delay);
} catch (InterruptedException ignored) {
}
System.out.println("完成: " + name);
}
}