Convert The First Letter Of Every Word In A String To Uppercase?

I'm trying to convert the first letter of every word in a String to uppercase. I've managed to isolate the first letter of every word and then make it uppercase but I don't know how to replace it.

public static StringBuffer makeUpperCase(){
String str = String.valueOf(input2);
for(int i = 0; i < str.length(); i++){
if(str.charAt(i) == ' '){
char var = str.charAt(i + 1);
var = Character.toUpperCase(var);
System.out.println(var);
}
}