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

How about:

StringBuilder builder = new StringBuilder();
for(int i=99;i>=0;i--){
    builder.append(Integer.toString(i));
}
builder.toString();

OR

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

But with this, you are making the operation O(N^2) instead of O(N).

Snippet from java docs:

Inserts the string representation of the Object argument into this character sequence. The overall effect is exactly as if the second argument were converted to a string by the method String.valueOf(Object), and the characters of that string were then inserted into this character sequence at the indicated offset.