java: use StringBuilder to insert at the beginning

Question

I could only do this with String, for example:

String str=\"\";
for(int i=0;i<100;i++){
    str=i+str;
}

Is there a way to achieve this wit

Answer 1

you can use strbuilder.insert(0,i);

Answer 2

As an alternative solution you can use a LIFO structure (like a stack) to store all the strings and when you are done just take them all out and put them into the StringBuilder. It naturally reverses the order of the items (strings) placed in it.

Stack<String> textStack = new Stack<String>();
// push the strings to the stack
while(!isReadingTextDone()) {
    String text = readText();
    textStack.push(text);
}
// pop the strings and add to the text builder
String builder = new StringBuilder(); 
while (!textStack.empty()) {
      builder.append(textStack.pop());
}
// get the final string
String finalText =  builder.toString();

Answer 3

You can use the insert method with the offset. as offset set to '0' means you are appending to the front of your StringBuilder.

StringBuilder sb = new StringBuilder();
for(int i=0;i<100;i++){
    sb.insert(0,i);
}

NOTE: as the insert method accept all types of primitives, you can use for int, long, char[] etc.