Avoid String charAt() method inside loops

Is there any effect on Code Optimization(Speed etc) if i replace ?

// Before

public void test(String str)  
{
     for(int i=0; i<str.length(); i++)
     {      
          System.out.println(str.charAt(i)); // VIOLATION 
     }
}

The above Code Snippet with below code :-

// After

public void test(String str)
{      
     char[] ch = str.toCharArray(); // CORRECTION
     for(int i=0; i < ch.length; i++) 
     {             
          System.out.println(ch[i]); // CORRECTION    
     }
}