JAVA 求昨天今天明天

   java.text.SimpleDateFormat df=new java.text.SimpleDateFormat("yyyy-MM-dd");
    java.util.Calendar calendar=java.util.Calendar.getInstance();
    calendar.roll(java.util.Calendar.DAY_OF_YEAR,-1);
    System.out.println("昨天："+df.format(calendar.getTime()));
    calendar=java.util.Calendar.getInstance();
    System.out.println("今天："+df.format(calendar.getTime()));
    calendar.roll(java.util.Calendar.DAY_OF_YEAR,1);
    System.out.println("明天："+df.format(calendar.getTime()));