public class Main 
{
	public static void main(String[] args) 
	{
		String dashes = "___";
		
		char[] charArray = dashes.toCharArray();
		
		charArray[1] = 'o';
		
		dashes = String.copyValueOf(charArray);
		
		System.out.println(dashes); // will output _o_
	}

}