How To Put All Char In Loop To String

I can't figure out how to have all of the random characters generated to go into the String. Below I can only get the last character to covert over to a String.

System.out.println("Original random character string:");
String printingString = "a";
for (int i = 0; i < 50; i++)//loop to obtain 50 random characters
{
char randomChar = (char) ((Math.random() * 255) +32);
System.out.print(randomChar);
printingString = Character.toString(randomChar); }
return printingString; }