JUC之創建線程的四種方式

一、繼承Thread類

通過自定義類繼承Thread類來創建

class MyThread extends Thread {
    @Override
    public void run() {
        for (int i = 0; i < 10; i++) {
            System.out.println(Thread.currentThread().getName() + "----" + i);
        }
    }
}

public class ThreadDemo {
    public static void main(String[] args) {
        System.out.println(Thread.currentThread().getName() + " === main");
        MyThread myThread = new MyThread();
        myThread.start();
    }
}

二、實現Runable接口

1. 通過自定義類實現Runable接口來創建

class MyThread implements Runnable {
    @Override
    public void run() {
        for (int i = 0; i < 10; i++) {
            System.out.println(Thread.currentThread().getName() + "----" + i);
        }
    }
}

public class ThreadDemo {
    public static void main(String[] args) {
        System.out.println(Thread.currentThread().getName() + " === main");
        Thread thread = new Thread(new MyThread());
        thread.start();
    }
}

2. 使用匿名內部類來是實現

public class ThreadDemo {
    public static void main(String[] args) {
        System.out.println(Thread.currentThread().getName() + " === main");
        Thread thread = new Thread(new Runnable() {
            @Override
            public void run() {
                for (int i = 0; i < 10; i++) {
                    System.out.println(Thread.currentThread().getName() + "----" + i);
                }
            }
        });
        thread.start();
    }
}

3. 使用lambda表達式來創建

public class ThreadDemo {
    public static void main(String[] args) {
        System.out.println(Thread.currentThread().getName() + " === main");
        new Thread(() -> {
            for (int i = 0; i < 10; i++) {
                System.out.println(Thread.currentThread().getName() + "----" + i);
            }
        },"My Thread").start();
    }
}

三、實現Callable接口

通過Callable來創建線程，可以有返回值

1. 自定義類實現Collable接口

class MyThread implements Callable<String> {
    @Override
    public String call() throws Exception {
        System.out.println(Thread.currentThread().getName());
        return "hello world";
    }
}

public class ThreadDemo {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        FutureTask futureTask = new FutureTask(new MyThread());
        Thread thread = new Thread(futureTask);
        thread.start();
        // 獲取返回值
        System.out.println(futureTask.get());
    }
}

• 對於同一個FutureTask，不管你通過它創建多少個線程，返回值結果都是一樣的。

2. Runbale與Callable的區別

• Callable實現的方法是call(),Runnable實現的方法是run().
• Callable的任務執行後有返回值，而Runnable的任務沒有返回值
• call方法可以拋出異常，run方法不可以
• 運行Callable任務可以拿到一個Future對象，表示異步計算的結果。它提供了檢查計算是否完成的方法，以等待計算的完成，並檢索計算的結果。通過Future對象可以瞭解任務執行情況，可取消任務的執行，還可獲取執行結果。

四、線程池

newFixedThreadPool

線程的數量有自己指定

public class ThreadDemo {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        ExecutorService executorService = Executors.newFixedThreadPool(5);
        for (int i = 0; i < 10; i++) {
            executorService.execute(new Runnable() {
                @Override
                public void run() {
                    System.out.println("線程 " + Thread.currentThread().getName() + " 被調用了");
                }
            });
        }
        executorService.shutdown();
    }
}

newSingleThreadExecutor

只有一個線程

public class ThreadDemo {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        ExecutorService executorService = Executors.newSingleThreadExecutor();
        for (int i = 0; i < 10; i++) {
            executorService.execute(new Runnable() {
                @Override
                public void run() {
                    System.out.println("線程 " + Thread.currentThread().getName() + " 被調用了");
                }
            });
        }
        executorService.shutdown();
    }
}

newCachedThread

根據任務多少來自動實現線程數的增減

public class ThreadDemo {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        ExecutorService executorService = Executors.newCachedThreadPool();
        for (int i = 0; i < 10; i++) {
            executorService.execute(new Runnable() {
                @Override
                public void run() {
                    System.out.println("線程 " + Thread.currentThread().getName() + " 被調用了");
                }
            });
        }
        executorService.shutdown();
    }
}