如何在java中处理日期

我有一个java程序，我可以在yyyy-MM-dd中设置一个日期，我可以从中获得下一个和上一个日期。以下方法可以完成这项工作

public void setDate(String date) {
        StringTokenizer st = new StringTokenizer(date, "-");
        year = Integer.parseInt(st.nextToken());
        monthNo = Integer.parseInt(st.nextToken()) - 1;
        day = Integer.parseInt(st.nextToken());
        date = year + "-" + monthNo + "-" + day;        
    }    

public String getPreviousMonth(boolean maxDate) {
            Calendar calendar = Calendar.getInstance();

            if (maxDate) {
                calendar.set(year, monthNo, 1);
                int maxD = calendar.getActualMaximum(calendar.DAY_OF_MONTH);
                 calendar.set(year, monthNo, maxD);
            } else {
                calendar.set(year, monthNo, day);
            }

            if (monthNo == 0) {
                calendar.add(calendar.MONTH, -1);
            } else {
                calendar.add(calendar.MONTH, -1);
            }
            String date = (calendar.get(calendar.YEAR)) + "-" + (calendar.get(calendar.MONTH) + 1) + "-" + calendar.get(calendar.DAY_OF_MONTH);
            calendar.clear();
            return date;
        }

        public String getNextMonth(boolean maxDate) {
            Calendar calendar = Calendar.getInstance();

            if (maxDate) {
                calendar.set(year, monthNo, 1);
                int maxD = calendar.getActualMaximum(calendar.DAY_OF_MONTH);
                calendar.set(year, monthNo, maxD);
            } else {
                calendar.set(year, monthNo, day);
            }
            if (monthNo == 11) {
                calendar.add(calendar.MONTH, 1);
            } else {
                calendar.add(calendar.MONTH, 1);
            }




    public String getCurrentMonth(boolean maxDate){
            Calendar calendar = Calendar.getInstance();
            if (maxDate) {
                calendar.set(year, monthNo, 1);
                int maxD = calendar.getActualMaximum(calendar.DAY_OF_MONTH);
                calendar.set(year, monthNo, maxD);
            } else {
                calendar.set(year, monthNo, day);
            }
            String date = (calendar.get(calendar.YEAR)) + "-" + (calendar.get(calendar.MONTH) + 1) + "-" + calendar.get(calendar.DAY_OF_MONTH);
            calendar.clear();
            return date;
        }

当我将日期设置为1月和2月时，它会给出正确的输出，但如果我选择1月和2月以外的其他月份，则无法获得正确的日期， 以下是一些结果

this is OK
2012-1-31 - current month
2011-12-31 - previous month
2012-2-29 - next month

2012-2-29 current month
2012-1-29 previous month ***day should be 31
2012-3-29 next month ***day should be 31

this is OK
2011-12-31 current month
2011-11-30 previous month
2012-1-31 next month

2011-11-30 current month
2011-10-30 previous month *** this should be 31
2011-12-30 next month *** this should be 31

this is OK
2011-12-31 current month
2011-11-30 previous month
2012-1-31 next month

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请告诉我我错在哪里…

为您安排下一个月的行程。上个月也需要做同样的事情。请参见下面与代码内联的注释：

  public String getNextMonth(boolean maxDate) {
        Calendar calendar = Calendar.getInstance();

        if (maxDate) {
            calendar.set(year, monthNo, 1);
            /* Move these two lines to end of method.
            int maxD = calendar.getActualMaximum(calendar.DAY_OF_MONTH);
            calendar.set(year, monthNo, maxD);
             */
        } else {
            calendar.set(year, monthNo, day);
        }
        //Not sure why have you used if/else. Both are doing the same thing
        if (monthNo == 11) {
            calendar.add(calendar.MONTH, 1);
        } else {
            calendar.add(calendar.MONTH, 1);
        }
        //here i.e. After you have calculated your next month.
        int maxD = calendar.getActualMaximum(calendar.DAY_OF_MONTH);
        calendar.set(year, monthNo, maxD);

    }

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问题是您在实际更改月份之前检索到了当月的最大天数。
这里应该是什么样子

public String getNextMonth(boolean maxDate) {
    Calendar calendar = Calendar.getInstance();
    calendar.set(year, monthNo, 1);
    calendar.add(Calendar.MONTH, 1);
    if (maxDate) {
        int maxD = calendar.getActualMaximum(Calendar.DAY_OF_MONTH);
        calendar.set(Calendar.DAY_OF_MONTH, maxD);
    } else {
        calendar.set(Calendar.DAY_OF_MONTH, day);
    }
    String date = (calendar.get(Calendar.YEAR)) + "-" + (calendar.get(Calendar.MONTH) + 1) + "-" + calendar.get(Calendar.DAY_OF_MONTH);
    calendar.clear();
    return date;
}

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顺便说一句，getNExtMonth不会出现。