Summary of how to create threads in java

1. Inherit the Thread class

public class ThreadCreator extends Thread{

    public static void main(String[] args) {
       //第一种方式：
       ThreadCreator creator = new ThreadCreator();
       Thread thread = new Thread(creator,"线程1");
       thread.start();
       //第二种方式：
       Thread thread = new ThreadCreator();
       thread.start();
       //第三种方式：
       new ThreadCreator().start();
　　　}
 
    @Override
    public void run() {
        System.out.println(Thread.currentThread().getName() + "run");
    }
}

2. Implement the Runnable interface

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public class ThreadCreator implements Runnable{

    public static void main(String[] args) {
       ThreadCreator creator = new ThreadCreator();
       Thread thread = new Thread(creator,"线程1");
       thread.start();
    }

    @Override
    public void run() {
        System.out.println(Thread.currentThread().getName() + "run");
    }
}

3. Implement the Callable interface

public class ThreadCreator implements Callable<Integer> {

    public static void main(String[] args) throws ExecutionException, InterruptedException {
       ThreadCreator creator = new ThreadCreator();
       FutureTask futureTask = new FutureTask(creator);
       Thread thread = new Thread(futureTask,"线程");
       thread.start();
       System.out.println(futureTask.get());
    }

    @Override
    public Integer call() {
        return 1024;
    }
}

4. Thread pool ExecutorService

public class ThreadCreator{

   static ExecutorService service = Executors.newFixedThreadPool(5);

    public static void main(String[] args) throws ExecutionException, InterruptedException {
        //execute无返回值
        service.execute(new ThreadTask(1,"1"));
        //submit有返回值
        Future<Integer> result = service.submit(new ThreadTaskCall());
        System.out.println(result.get());
        service.shutdownNow();
    }
    static class ThreadTask implements Runnable{
        private int param1;
        private String param2;
        public ThreadTask(int param3,String param4){
            this.param1 = param3;
            this.param2 = param4;
        }
        @Override
        public void run() {
            System.out.println(param1+param2);
        }
    }

    static class ThreadTaskCall implements Callable<Integer>{
        @Override
        public Integer call() throws Exception {
            return 1024;
        }
    }
}

The difference between submit and execute in the thread pool:

(1 ) The acceptable task types are different: execute can only accept Runnable tasks, and submit can also accept Callable tasks.

(2) Return value: execute has no return value. Once the task is submitted, the execution result cannot be monitored in the current thread. Submit has a Future type return value, which is used to receive return values ​​or respond to exceptions. Obtained through the get() method.

The bottom layer of submit is still called execute, but it is encapsulated with a future layer on this basis, and all exceptions generated during the execution are encapsulated in a variable:

public void run() {
        if (state != NEW ||
            !UNSAFE.compareAndSwapObject(this, runnerOffset,
                                         null, Thread.currentThread()))
            return;
        try {
            Callable<V> c = callable;
            if (c != null && state == NEW) {
                V result;
                boolean ran;
                try {
                    result = c.call();
                    ran = true;
                } catch (Throwable ex) {
                    result = null;
                    ran = false;
                    setException(ex);
                }
                if (ran)
                    set(result);
            }
        } finally {
            runner = null;
            int s = state;
            if (s >= INTERRUPTING)
                handlePossibleCancellationInterrupt(s);
        }
    }
protected void setException(Throwable t) {
        if (UNSAFE.compareAndSwapInt(this, stateOffset, NEW, COMPLETING)) {
            outcome = t;
            UNSAFE.putOrderedInt(this, stateOffset, EXCEPTIONAL); // final state
            finishCompletion();
        }
    }

In addition, spring The schedule annotation uses the submit processing method for reference.

5. Anonymous inner class

public class ThreadCreator {

    public static void main(String[] args) {

        //继承Thread类
        new Thread() {
            @Override
            public void run() {
                System.out.println("extends Thread Class!");
            }
        }.start();
        //实现Runnable接口
        new Thread(new Runnable() {
            @Override
            public void run() {
                System.out.println("implement Runnable!");
            }
        }).start();
        //实现Callable接口
        new Thread(new FutureTask<Integer>(new Callable() {
            @Override
            public Integer call() throws Exception {
                return 1024;
            }
        })).start();
        //lambda表达式
        new Thread(() -> System.out.println("execute single code")).start();
        new Thread(() -> {
            System.out.println("execute multiple code");
        }).start();
    }
}

lambda thread pool:

public class ThreadCreator {

    static ExecutorService service = Executors.newFixedThreadPool(5);

    static List list = new ArrayList();

    public static void main(String[] args) {
        service.execute(() -> execute()); //无返回值
        Future future = service.submit(() -> execute()); //有返回值
        list.add(future);
    }

    public static void execute() {
        //do something
    }
}

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