How to create threads

How to create threads

Method 1 , Use it directly Thread

//  The argument to the constructor is to assign a name to the thread , recommend 
Thread t1 = new Thread("t1") {
    
 @Override
 // run  Method implements the task to be executed 
 public void run() {
    
 log.debug("hello");
 }
};
t1.start();

Method 2 , Use Runnable coordination Thread

hold 【 Threads 】 and 【 Mission 】（ Code to execute ） Separate

• Thread On behalf of thread
• Runnable Runnable tasks （ The code to be executed by the thread

//  Create task object 
Runnable task2 = new Runnable() {
    
 @Override
 public void run() {
    
 log.debug("hello");
 }
};
//  Parameters 1  It's the object of the mission ;  Parameters 2  It's the thread name , recommend 
Thread t2 = new Thread(task2, "t2");
t2.start();

Method 3 ,Callable

Runnable One function of the interface is , When the thread terminates （ namely run(） When finished ）, We can't make the thread return results . To support secondary functions ,Java Provides Callable Interface .

• In order to achieve Runnable, You need to realize that you don't regret anything run（） Method , And for Callable Interface , You need to return the result on completion Call（） Method
• call() Method can throw an exception , and run() no way
• In order to achieve Callable It has to be rewritten call Method

Threadl Constructors in classes cannot be passed Callable Of , It can only be transmitted Runnable

So it is wrong to create threads in this way ：

new Thread(new Callable(),"tt").start()

Thread Can only

```java
new Thread(new Runnable(),"tt").start()

Then you must find a class , Make it both Runnable It matters , And also Callable It matters ,,,FeatureTask,FeatureTask yes Runnable Implementation class , At the same time, its constructor can transmit Callable, That's it Callable And Runnable The associated .

1、Callable And Runnable The difference between

1)Callable The prescribed method is call(),Runnable The prescribed method is run().

(2)Callable After the task is executed, it can return the value , and Runnable The task of cannot return a value

(3)call Methods can throw exceptions ,run Method can not

(4) function Callable The mission can get a Future object ,Future Represents the result of an asynchronous calculation

2、Callable combination futureTask Create execution tasks , Pass the task to Thread in , Then start the execution of the task

public class CallableDemo {
    

    public static void main(String[] args) throws ExecutionException, InterruptedException {
    

        FutureTask futureTaskTest = new FutureTask(new Callable() {
    
            @Override
            public Integer call() throws Exception {
    
                System.out.println("callable1");
                return 1024;
            }
        });

        FutureTask futureTask = new FutureTask(()->{
    
            System.out.println("callable2");
            return 2048;
        });

        new Thread(futureTask,"t1").start();


        while (!futureTask.isDone()){
    
            System.out.println(" adopt isDone You can judge whether the task is over ");
        }
        System.out.println(" adopt get Method can obtain the execution result of the task ");
        System.out.println(futureTask.get());


    }
}

 adopt isDone You can judge whether the task is over 
 adopt isDone You can judge whether the task is over 
 adopt isDone You can judge whether the task is over 
 adopt isDone You can judge whether the task is over 
 adopt isDone You can judge whether the task is over 
 adopt isDone You can judge whether the task is over 
 adopt isDone You can judge whether the task is over 
 adopt isDone You can judge whether the task is over 
 adopt isDone You can judge whether the task is over 
 adopt isDone You can judge whether the task is over 
 adopt isDone You can judge whether the task is over 
 adopt isDone You can judge whether the task is over 
 adopt isDone You can judge whether the task is over 
 adopt isDone You can judge whether the task is over 
 adopt get Method can obtain the execution result of the task 
2048

3**、FutureTask The details of the ：**

• get Method location , It's usually on the last line , Otherwise, the main thread will block in get Wait for it to return

public class CallableDemo {
    

    public static void main(String[] args) throws ExecutionException, InterruptedException {
    

        FutureTask futureTask = new FutureTask(()->{
    
            System.out.println("callable2");
            Thread.sleep(10000);
            return 2048;
        });


        System.out.println(" Task start ："+   System.currentTimeMillis());
        new Thread(futureTask,"t1").start();
        System.out.println(futureTask.get());
        System.out.println("main Thread end ："+   System.currentTimeMillis());

    }
}

 Task start ：1657859321584
callable2
2048
main Thread end ：1657859331587

public class CallableDemo {
    

    public static void main(String[] args) throws ExecutionException, InterruptedException {
    

        FutureTask futureTask = new FutureTask(()->{
    
            System.out.println("callable2");
            Thread.sleep(10000);
            return 2048;
        });


        System.out.println(" Task start ："+   System.currentTimeMillis());
        new Thread(futureTask,"t1").start();
        System.out.println("main Thread end ："+   System.currentTimeMillis());
        System.out.println(futureTask.get());
    }
}

 Task start ：1657859359366
main Thread end ：1657859359366
callable2
2048

• The task is performed only once

Next, two threads are started t1、t2 Perform tasks , It can be seen from the print results that the task was executed only once

public class CallableDemo {
    

    public static void main(String[] args) throws ExecutionException, InterruptedException {
    

        FutureTask futureTask = new FutureTask(()->{
    
            System.out.println("callable");
            return 2048;
        });
        
        new Thread(futureTask,"t1").start();
        new Thread(futureTask,"t2").start();
        System.out.println(futureTask.get());
    }
}

callable
2048