How Java Compile Works When two String Object is Available

Hello Everyone, I am new to java and working on a project. I am facing some errors which I mentioned below. Can anyone check this? where i am wrong?

 class Simple{  
     public static void main(String args[]){  
         String s="Sachin"+" Tendulkar";  
         System.out.println(s);//Sachin Tendulkar  

I am using online java compiler here and the compiler transforms is:

 String s = (new StringBuilder()).append("Sachin").append(" Tendulkar").toString();  

What is mean by last line? Can anyone explain me?