question: public static String replace ( String text , String oldsub , String newsub , boolean caseInsensitive , boolean firstOnly ) { StringBuilder buf ; int tln ; int oln = oldsub . length ( ) ; if ( oln == 0 ) { int nln = newsub . length ( ) ; if ( nln == 0 ) { return text ; } else { if ( firstOnly ) { return newsub + text ; } else { tln = text . length ( ) ; buf = new StringBuilder ( tln + ( tln + 1 ) * nln ) ; buf . append ( newsub ) ; for ( int i = 0 ; i < tln ; i ++ ) { buf . append ( text . charAt ( i ) ) ; buf . append ( newsub ) ; } return buf . toString ( ) ; } } } else { oldsub = caseInsensitive ? oldsub . toLowerCase ( ) : oldsub ; String input = caseInsensitive ? text . toLowerCase ( ) : text ; int e = input . indexOf ( oldsub ) ; if ( e == - 1 ) { return text ; } int b = 0 ; tln = text . length ( ) ; buf = new StringBuilder ( tln + Math . max ( newsub . length ( ) - oln , 0 ) * 3 ) ; do { buf . append ( text . substring ( b , e ) ) ; buf . append ( newsub ) ; b = e + oln ; e = input . indexOf ( oldsub , b ) ; } while ( e != - 1 && ! firstOnly ) ; buf . append ( text . substring ( b ) ) ; return buf . toString ( ) ; } }
target:  Replaces all occurrences of a sub-string in a string.