How to add one day to a date?

Given a Date dt you have several possibilities:

Solution 1: You can use the Calendar class for that:

Date dt = new Date();
Calendar c = Calendar.getInstance(); 
c.setTime(dt); 
c.add(Calendar.DATE, 1);
dt = c.getTime();

Solution 2: You should seriously consider using the Joda-Time library, because of the various shortcomings of the Date class. With Joda-Time you can do the following:

Date dt = new Date();
DateTime dtOrg = new DateTime(dt);
DateTime dtPlusOne = dtOrg.plusDays(1);

Solution 3: With Java 8 you can also use the new JSR 310 API (which is inspired by Joda-Time):

Date dt = new Date();
LocalDateTime.from(dt.toInstant()).plusDays(1);

Date today = new Date();
Date tomorrow = new Date(today.getTime() + (1000 * 60 * 60 * 24));

Date has a constructor using the milliseconds since the UNIX-epoch. the getTime()-method gives you that value. So adding the milliseconds for a day, does the trick. If you want to do such manipulations regularly I recommend to define constants for the values.

Important hint: That is not correct in all cases. Read the WARNING comment, below.