Java高併發,建立執行緒的新方式Callable介面
阿新 • • 發佈:2020-08-22
我們已經知道建立執行緒的方式有1.繼承thread類。2.實現Runnable介面
接下來講建立執行緒的新方式Callable介面,首先對比一下Runnable介面和Callable介面的區別:
首先建立兩個資源類:分別是實現了Runnable介面和實現了Callable介面:
//Runnable介面 class MyThreadRunnable implements Runnable { @Override public void run() { } } //Callable class MyThreadCallable implements Callable<Integer> { @Overridepublic Integer call() throws Exception { System.out.println("******come in here"); return 1024; } }
我們可以看到Callable存在泛型,以及返回值,這是對原來的老技術的增強,因為存在了返回值,提高了執行緒的細粒度。
接著我們看看Runnable建立執行緒的方式:
//Runnable MyThreadRunnable myThread1=new MyThreadRunnable(); Thread t1=new Thread(myThread1);
但是通過該方式我們利用Callable來建立執行緒,卻報錯了,這是為什麼 呢?
原因:Thread並不存在Callable的構造器!
如何建立Callable執行緒
首先檢視API,看Runable介面:
過程如下:
我們可以看到的是,這個構造器需要的引數就是Callable介面的實現類。
所以,我們建立執行緒的方式如下:
public class CallableDemo { public static void main(String[] args) { // MyThreadCallable myThread = new MyThreadCallable(); FutureTask futureTask = newFutureTask(new MyThreadCallable()); new Thread(futureTask, "A").start(); System.out.println(futureTask.get());// 1024 通過get方法來獲取返回值 } }
get方法具有阻塞的效果
public class CallableDemo { public static void main(String[] args) throws ExecutionException, InterruptedException { // MyThreadCallable myThread = new MyThreadCallable(); FutureTask futureTask = new FutureTask(new MyThreadCallable()); new Thread(futureTask, "A").start(); System.out.println(futureTask.get());// 1024 通過get方式來獲取返回值 該方法會阻塞! System.out.println(Thread.currentThread().getName()+"***計算完成"); } } //Callable class MyThreadCallable implements Callable<Integer> { @Override public Integer call() throws Exception { System.out.println("******come in here"); Thread.sleep(5000); return 1024; } }
futureTask的單一性
新增一個執行緒B:
public class CallableDemo { public static void main(String[] args) throws ExecutionException, InterruptedException { // MyThreadCallable myThread = new MyThreadCallable(); FutureTask futureTask = new FutureTask(new MyThreadCallable()); new Thread(futureTask, "A").start(); new Thread(futureTask, "B").start(); System.out.println(Thread.currentThread().getName() + "***計算完成"); System.out.println(futureTask.get());// 1024 通過get方式來獲取返回值 該方法會阻塞! } } //Callable class MyThreadCallable implements Callable<Integer> { @Override public Integer call() throws Exception { System.out.println("******come in here"); Thread.sleep(5000); return 1024; } }
只執行了一次,因為一個futureTask,不管幾個執行緒呼叫,呼叫的都是同一個futureTask物件!而且Runnable介面就不一樣了:
public class CallableDemo { public static void main(String[] args) throws ExecutionException, InterruptedException { MyThreadRunnable t = new MyThreadRunnable(); Thread thread = new Thread(t); new Thread(thread).run(); new Thread(thread).run(); } } //Runnable介面 class MyThreadRunnable implements Runnable { @Override public void run() { System.out.println("******come in here"); } }
以上..