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最近在学习并发，于是我在网上搜了一本《java并发编程实战》书学习。
在我印象中创建线程有两种方式
1. 继承Thread类，重写run方法，实例化自己写Thread子类，并用start()方法开启。
2.实现Runnable接口，重写run方法，把Runnable的子类的实例对象作为Thread的构造参数传递进去，创建线程，并开启。
但是我看别人代码时大部分都用第一种方式，直接new Thread 然后重写run方法。其实第二种方式更加符合面向对象的编程，因为，Thread是一个线程，他只管创建和开启线程，而不应该进行逻辑的处理代码写到里面，逻辑处理应该交给Runnable的子类的进行。
传统定时器是Timer类，创建方式
Timer timer = new Timer();
timer.schedule(new TimerTask(){ //创建定时器任务
@Override
public void run() {
System.out.println("你好");
}
},2000); //2秒之后打印你好
timer.schedule(new TimerTask(){
@Override
public void run() {
System.out.println("你好");
}
},2000,3000); //2秒之后打印你好,接着每3秒打印一次你好。
此处有个要求，需要在2之后打印你好，3秒之后打印世界...，然后不断的循环打印下去。该怎么办？
思路：1.我可以创建两个定时器任务，task1任务2秒后打印你好，task2任务3秒后打印，然后在task1任务结束时开启task2，在task2结束时开启task1
2.可以只创建一个task ，让后在外部做一个 flag标记，当为true是执行打印你好，然后在结束时开启一个新任务，并把flag=!flag;
//第一种实现
public static void main(String[] args) {
new Timer().schedule(new MyTimerTask1(), 2000);
while (true) {
System.out.println(new Date().getSeconds());
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
static class MyTimerTask1 extends TimerTask {
@Override
public void run() {
System.out.println("hello");
new Timer().schedule(new MyTimerTask2(), 3000);
}
}
static class MyTimerTask2 extends TimerTask {
@Override
public void run() {
System.out.println("wrold");
new Timer().schedule(new MyTimerTask1(), 2000);
}
}
}
第二种可以就不贴了。
使用Executors工具类进行创建线程池
API的介绍：
newFixedThreadPool 创建一个固定长度的线程池，当到达线程最大数量时，线程池的规模将不再变化。
newCachedThreadPool 创建一个可缓存的线程池，如果当前线程池的规模超出了处理需求，将回收空的线程；当需求增加时，会增加线程数量；线程池规模无限制。
newSingleThreadPoolExecutor 创建一个单线程的Executor，确保任务对了，串行执行（此单个线程死之后又会有个线程代替他）
public static void main(String[] args) {
ExecutorService threadPool = Executors.newFixedThreadPool(3); //第1种
// ExecutorService threadPool = Executors.newCachedThreadPool();//第2种
// ExecutorService threadPool = Executors.newSingleThreadExecutor();//第3种
for (int i = 1; i <= 10; i++) {
final int task = i;
threadPool.execute(new Runnable() {
@Override
public void run() {
for (int j = 1; j <= 5; j++) {
try {
Thread.sleep(20);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println(Thread.currentThread().getName()
+ " is looping of " + j + " for task of "
+ task);
}
}
});
}
}
把10个任务交个3种线程池去完成，
结果
第1种的结果 10个任务只有个开起固定的3个线程去完成任务 pool-1-thread-1 is looping of 1 for task of 1 pool-1-thread-3 is looping of 1 for task of 3 pool-1-thread-2 is looping of 1 for task of 2 pool-1-thread-1 is looping of 2 for task of 1 pool-1-thread-2 is looping of 2 for task of 2 pool-1-thread-3 is looping of 2 for task of 3 pool-1-thread-2 is looping of 1 for task of 6 pool-1-thread-1 is looping of 1 for task of 4 pool-1-thread-3 is looping of 1 for task of 5 pool-1-thread-3 is looping of 2 for task of 5 pool-1-thread-3 is looping of 3 for task of 3 pool-1-thread-2 is looping of 4 for task of 2 第2种的结果 10个任务开起了10个线程去完成 pool-1-thread-1 is looping of 1 for task of 1 pool-1-thread-3 is looping of 1 for task of 3 pool-1-thread-2 is looping of 1 for task of 2 pool-1-thread-9 is looping of 1 for task of 9 pool-1-thread-10 is looping of 1 for task of 10 pool-1-thread-6 is looping of 1 for task of 6 pool-1-thread-5 is looping of 1 for task of 5 pool-1-thread-4 is looping of 1 for task of 4 pool-1-thread-8 is looping of 1 for task of 8 pool-1-thread-7 is looping of 1 for task of 7 pool-1-thread-3 is looping of 2 for task of 3 pool-1-thread-1 is looping of 2 for task of 1 pool-1-thread-2 is looping of 2 for task of 2 pool-1-thread-7 is looping of 2 for task of 7 pool-1-thread-4 is looping of 2 for task of 4 pool-1-thread-5 is looping of 2 for task of 5 pool-1-thread-9 is looping of 2 for task of 9 pool-1-thread-8 is looping of 2 for task of 8 pool-1-thread-6 is looping of 2 for task of 6 pool-1-thread-10 is looping of 2 for task of 10 第3种的结果 10个任务却只开启了一个线程 pool-1-thread-1 is looping of 1 for task of 1 pool-1-thread-1 is looping of 2 for task of 1 pool-1-thread-1 is looping of 1 for task of 2 pool-1-thread-1 is looping of 2 for task of 2 pool-1-thread-1 is looping of 1 for task of 3 pool-1-thread-1 is looping of 2 for task of 3 pool-1-thread-1 is looping of 1 for task of 4 pool-1-thread-1 is looping of 2 for task of 4 pool-1-thread-1 is looping of 1 for task of 5 pool-1-thread-1 is looping of 2 for task of 5 pool-1-thread-1 is looping of 1 for task of 6 pool-1-thread-1 is looping of 2 for task of 6 pool-1-thread-1 is looping of 1 for task of 7 pool-1-thread-1 is looping of 2 for task of 7 pool-1-thread-1 is looping of 1 for task of 8 pool-1-thread-1 is looping of 2 for task of 8 pool-1-thread-1 is looping of 1 for task of 9 pool-1-thread-1 is looping of 2 for task of 9 pool-1-thread-1 is looping of 1 for task of 10 pool-1-thread-1 is looping of 2 for task of 10
newScheduledThreadPool是创建定时器 和Timer差不多，但Timer内部只有一个线程进行执行任务，而newScheduledThreadPool是可以设置多个线程的
Executors.newScheduledThreadPool(3).scheduleAtFixedRate(new Runnable() {
@Override
public void run() {
System.out.println("bombing!");
}
}, 6, 2, TimeUnit.SECONDS);
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原文地址：http://my.oschina.net/qiuhoude/blog/388039
