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This article will explain in detail what is the difference between the start and run methods of Thread. The content of the article is of high quality, so the editor will share it with you for reference. I hope you will have a certain understanding of the relevant knowledge after reading this article.

Start () and run () in Thread are the two most important methods of Java's multithreading concept. I believe that in Java learning, you will be more or less confused about the difference between the two. So the editor came to talk to you about start and run methods, including: understanding start and run methods, the difference between the two, code examples and thread state instructions.

First, know the start and run methods of Thread.

1. What is the start () method in Java?

The start () method of the thread class can be used to start the thread; it internally calls the run () method of the Runnable interface to execute the code specified in the run () method in a separate thread.

The start () method starts the thread to perform the following tasks:

It counts a new thread.

The thread moves from New State to the Runnable state.

When a thread has a chance to execute, its target run () method will run.

2. What is the run () method in Java?

The run () method of the thread class is an abstract method of the Runnable interface that is called directly by the java virtual machine and does not create a new thread.

Second, the difference between start () method and run () method.

1. Definition of method

The start () method is defined in the java. Lang. Thread class, while the run () method is defined in the java.lang.Runnable interface and must be overridden in the implementation class.

2. Create a new thread

When the program calls the start () method, it creates a new thread and then executes the run () method. But if we call the run () method directly, no new thread will be created, the run () method will be executed as a regular method call to the current calling thread itself, and multithreading will not occur.

3. Call multiple times

The start () method cannot be called multiple times, otherwise java.lang.IllegalStateException; is thrown and the run () method can be called multiple times because it is just a normal method call.

3. Code example:

Start the thread through start, start asynchronously

Public static void?main (String args []) {

Thread t = new?Thread () {

Public void?run () {

Pong ()

}

}

T.start ()

System.out.print ("ping")

}

Static?void?pong () {

System.out.print ("pong")

}

Output: pingpong

Start the thread through run, start synchronously

Public static void main (String args []) {

Thread t = new Thread () {

Public void run () {

Pong ()

}

}

T.run ()

System.out.print ("ping")

}

Static?void?pong () {

System.out.print ("pong")

}

Output: pongping

Through the above two program examples, you can easily tell the difference between the start () method and the run () method:

T.start (); this line of code is equivalent to starting a thread and operating asynchronously

T.run (); this line of code is equivalent to using the run method in the class t, which is just a common method of the main thread

IV. Description of thread status

From a large point of view, the thread state can be summarized as: initial state, runnable state, unrunnable state and extinct state, which are described as follows:

1) there are two ways to implement a thread, one is to inherit the Thread class, and the other is to implement the Runnable interface, but anyway, when we new the thread instance, the thread enters its initial state

2) when the object calls the start () method, it enters the runnable state

3) after entering the runnable state, when the object is selected by the operating system, the CPU time slice will enter the running state.

4) after entering the running state, there are many situations, such as the following:

A. after the end of the run () method or the main () method, the thread enters a terminated state

b. When a thread calls its own sleep () method or another thread's join () method, it enters a blocking state (which stops the current thread but does not release the occupied resources). When sleep () ends or join () ends, the thread enters a runnable state and continues to wait for OS to allocate time slices When the thread has just entered the runnable state (note that it is not running yet) and finds that the resource to be called is locked (synchroniza,lock), it will immediately enter the lock pool state and wait for the lock mark to be acquired (there may already be other threads in the lock pool waiting for the lock tag to be acquired, and they are in the queue state on a first-come-first-served basis). Once the thread has obtained the lock mark, it will go into the runnable state and wait for OS to allocate the CPU time slice.

c. When a thread calls the wait () method, it enters the waiting queue (this state releases all the resources it possesses, unlike the blocking state). After entering this state, it cannot wake up automatically. It must rely on other threads to call the notify () or notifyAll () method to be awakened (because notify () only wakes up a thread, but we are not sure which thread is waking up. Maybe the thread we need to wake up cannot be awakened, so in actual use, we usually use the notifyAll () method to wake up some threads. After being awakened, the thread will enter the lock pool and wait for the lock token to be obtained. When the thread calls the stop method, it can make the thread enter the extinction state, but because the stop method is not safe and is not encouraged to use, we can implement the thread stop through the condition modification in the run method.

What is the difference between Thread's start and run methods is shared here, I hope the above content can be of some help to you, you can learn more knowledge. If you think the article is good, you can share it for more people to see.

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