The following function getPart( ) is a part of some class which is used to extract h number of…

The following function getPart( ) is a part of some class which is used to extract h number of characters starting from index b of a string str. There are some places in the code marked by ?1?,?2?,?3? which must be replaced by an expression / statement so that the function works correctly.

String getPart(String str, int b, int h)
{
    int beg= ?1?;
    int end =b+h-1;
    String g="";
    while(beg<=?2? && beg>=0 && end<str.length() )
    {
        g+=str.charAt(beg);
        ?3?;
    }
    return g;
}