java decimal String format

"34.49596" would be "34.4959"
"49.3" would be "49.30"

DecimalFormat df = new DecimalFormat("0.00##");
String result = df.format(34.4959);

double a = 34.51234;

NumberFormat df = DecimalFormat.getInstance();
df.setMinimumFractionDigits(2);
df.setMaximumFractionDigits(4);
df.setRoundingMode(RoundingMode.DOWN);

System.out.println(df.format(a));