Diff between calling a start()->run() method AND calling run() method directly without start() method

If the run() method of a Thread is called directly without start() method. It fails to obey properties of Thread. It acts as a normal method.

Example: without using start()

 class ThreadA extends Thread { 
   ThreadA() { 
   } 
  
   public void run() { 
     for (int i = 0; i < 5; i++) { 
       System.out.println("I am in run method " + i + " " + this.getName()); 
       try { 
         this.sleep(500); 
       } catch (InterruptedException ie) { 
         System.out.println(ie); 
       } 
     } 
   } 
 } 
  
 public class Threadtest { 
   public Threadtest() { 
   } 
  
   public static void main(String[] args) { 
     Thread t1 = new Thread(new ThreadA(), "t1"); 
     Thread t2 = new Thread(new ThreadA(), "t2"); 
     t1.run(); 
     t2.run(); 
   } 
 } 

The output will be:
I am in run method 0 Thread-0
I am in run method 1 Thread-0
I am in run method 2 Thread-0
I am in run method 3 Thread-0
I am in run method 4 Thread-0
I am in run method 0 Thread-1
I am in run method 1 Thread-1
I am in run method 2 Thread-1
I am in run method 3 Thread-1
I am in run method 4 Thread-1

But,
if the lines t1.run() and t2.run() are replaced by t1.start() and t2.start() then the output is,

I am in run method 0 Thread-0
I am in run method 0 Thread-1
I am in run method 1 Thread-1
I am in run method 1 Thread-0
I am in run method 2 Thread-0
I am in run method 2 Thread-1
I am in run method 3 Thread-1
I am in run method 3 Thread-0
I am in run method 4 Thread-0
I am in run method 4 Thread-1