Difference between Thread.start() and Thread.run() in Java

In Java's multi-threading concept, start() and run() are the two most important methods. So what's the difference between them? The following article will introduce you to the start() and run() methods and introduce the differences between them. I hope it will be helpful to you.

The start() method in Java

The start() method of the thread class can be used Start a thread; this method internally calls the run() method of the Runnable interface to execute the code specified in the run() method in a separate thread. [Video tutorial recommendation: Java tutorial]

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

● It counts a new thread

● The thread moves from New State to Runnable state.

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

The run() method in Java

The run() method of the thread class is an abstract method of the Runnable interface, controlled by the java virtual machine If called directly, no new thread will be created.

The difference between start() method and run() method

1. Definition of method

# The ##start() method is defined in the java.lang.Thread class; and the run() method is defined in the java.lang.Runnable interface and must be rewritten in the implementation class.

2. New thread creation

When the program calls the start() method, a new thread will be created and then the run() method will be executed. 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 of the current calling thread itself, and no multi-threading will occur.

Example:

class MyThread extends Thread { 
    public void run() 
    { 
System.out.println("\n"); 
        System.out.println("当前线程的名称: "
                           + Thread.currentThread().getName()); 
        System.out.println("run()方法调用"); 
    } 
} 
  
class demo { 
    public static void main(String[] args) 
    { 
        MyThread t = new MyThread(); 
        t.start(); 
    } 
}

Output:

As we can see in the above example, when we call the thread class instance When the start() method is called, a new thread will be created with the default name Thread-0, and then the run() method will be called and everything will be executed in it. Newly created thread.

Now, let us try calling the run() method directly instead of the start() method:

class MyThread extends Thread { 
    public void run() 
    { 
System.out.println("\n"); 
        System.out.println("当前线程的名称: "
                           + Thread.currentThread().getName()); 
  
        System.out.println("run()方法调用"); 
    } 
} 
  
class GeeksforGeeks { 
    public static void main(String[] args) 
    { 
        MyThread t = new MyThread(); 
        t.run(); 
    } 
}

Output:

As we As you can see in the above example, when we call the run() method of the MyThread class, no new thread is created, and the run() method is executed on the current thread, the main thread. Therefore, no multithreading occurs. The run() method is called as a normal function.

3. Multiple calls

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

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