Java Hour 27 Concurrent
有句名言，叫做10000小时成为某一个领域的专家。姑且不辩论这句话是否正确，让我们到达10000小时的时候再回头来看吧。
27 Hours.
本小时主要过一下多线程相关的基本API.
Defining tasks
package mike.qian.hello; public class LiftOff implements Runnable { protected int countDown = 10; // Default private static int taskCount = 0; private final int id = taskCount++; public LiftOff() { } public LiftOff(int countDown) { this.countDown = countDown; } public String status() { return "#" + id + "(" + (countDown > 0 ? countDown : "Liftoff!") + "), "; } public void run() { while (countDown-- > 0) { System.out.print(status()); Thread.yield(); } } }
一个线程主要是为了驱动一个task. 只要实现一个Runnable 接口就表示这是一个task.
Thread.yield 这个是可选了，表明允许CPU从当前线程中滚出去干其他事情去。
package mike.qian.hello; public class Application { public static void main(String[] args) { Thread t = new Thread(new LiftOff()); t.start(); System.out.println("Waiting for LiftOff"); } }
package mike.qian.hello; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; public class Application { public static void main(String[] args) { ExecutorService exec = Executors.newCachedThreadPool(); for (int i = 0; i < 5; i++) exec.execute(new LiftOff()); exec.shutdown(); System.out.println("Waiting for LiftOff"); } }
带返回值的线程
package mike.qian.hello; import java.util.concurrent.Callable; class TaskWithResult implements Callable<String> { private int id; public TaskWithResult(int id) { this.id = id; } public String call() { return "result of TaskWithResult " + id; } }
package mike.qian.hello; import java.util.ArrayList; import java.util.concurrent.ExecutionException; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Future; public class Application { public static void main(String[] args) { ExecutorService exec = Executors.newCachedThreadPool(); ArrayList<Future<String>> results = new ArrayList<Future<String>>(); for (int i = 0; i < 10; i++) results.add(exec.submit(new TaskWithResult(i))); for (Future<String> fs : results) try { // get() blocks until completion: System.out.println(fs.get()); } catch (InterruptedException e) { System.out.println(e); return; } catch (ExecutionException e) { System.out.println(e); } finally { exec.shutdown(); } } }
看到这个future, 瞬间石化了，好山寨的命名。
守护线程
守护线程就是后台线程，当所有前台线程退出后，程序将退出。
内部类的使用
package mike.qian.hello; import java.util.concurrent.*; import static java.lang.System.out; // Using a named inner class: class InnerThread1 { private int countDown = 5; private Inner inner; private class Inner extends Thread { Inner(String name) { super(name); start(); } public void run() { try { while (true) { out.println(this); if (--countDown == 0) return; sleep(10); } } catch (InterruptedException e) { out.println("interrupted"); } } public String toString() { return getName() + ": " + countDown; } } public InnerThread1(String name) { inner = new Inner(name); } } // Using an anonymous inner class: class InnerThread2 { private int countDown = 5; private Thread t; public InnerThread2(String name) { t = new Thread(name) { public void run() { try { while (true) { out.println(this); if (--countDown == 0) return; sleep(10); } } catch (InterruptedException e) { } } public String toString() { return getName() + ": " + countDown; } }; t.start(); } } // Using a named Runnable implementation: class InnerRunnable1 { private int countDown = 5; private Inner inner; private class Inner implements Runnable { Thread t; Inner(String name) { t = new Thread(this, name); t.start(); } public void run() { try { while (true) { out.println(this); if (--countDown == 0) return; TimeUnit.MILLISECONDS.sleep(10); } } catch (InterruptedException e) { out.println("sleep() interrupted"); } } public String toString() { return t.getName() + ": " + countDown; } } public InnerRunnable1(String name) { inner = new Inner(name); } } // Using an anonymous Runnable implementation: class InnerRunnable2 { private int countDown = 5; private Thread t; public InnerRunnable2(String name) { t = new Thread(new Runnable() { public void run() { try { while (true) { out.println(this); if (--countDown == 0) return; TimeUnit.MILLISECONDS.sleep(10); } } catch (InterruptedException e) { out.println("sleep() interrupted"); } } public String toString() { return Thread.currentThread().getName() + ": " + countDown; } }, name); } } // A separate method to run some code as a task: class ThreadMethod { private int countDown = 5; private Thread t; private String name; public ThreadMethod(String name) { this.name = name; } public void runTask() { if (t == null) { t = new Thread(name) { public void run() { try { while (true) { out.println(this); if (--countDown == 0) return; sleep(10); } } catch (InterruptedException e) { out.println("sleep() interrupted"); } } public String toString() { return getName() + ": " + countDown; } }; t.start(); } } } public class Application { public static void main(String[] args) { new InnerThread1("InnerThread1"); new InnerThread2("InnerThread2"); new InnerRunnable1("InnerRunnable1"); new InnerRunnable2("InnerRunnable2"); new ThreadMethod("ThreadMethod").runTask(); } } /* (Execute to see output) */// :~
这里包含了内部类，匿名内部类，相关的内容下个小时补上。
后面茫茫多的内容
其实这块东西和.NET 大同小异，但是东西是茫茫多的，暂且略过不表。