請問如何得到上一個月的最後一天呢？
public static String ss(){Calendar cal=Calendar.getInstance();//当前日期cal.set(Calendar.DATE,1);//设为当前月的1号cal.add(Calendar.DATE,-1);//减一天，变为上月最后一天SimpleDateFormat simpleDateFormat = new SimpleDateFormat( "yyyy-MM-dd ");return simpleDateFormat.format(cal.getTime());//输出2005-04-30}package com.java.page;import java.text.SimpleDateFormat;import java.util.Calendar;import java.util.regex.Matcher;import java.util.regex.Pattern;public class Test {public static void main(String[] args) {Calendar cal=Calendar.getInstance();//当前日期//cal.set(Calendar.DATE,1);//设为当前月的1号//cal.add(Calendar.DATE,-1);//减一天，变为上月最后一天System.out.println("现在的时间是："+Calendar.MONTH);int n=5;String[] str = {"1月31号","2月29号","3月31号","4月30号","5月31号","6月30号","7月31号","8月31号","9月30号","10月31号","11月30号","12月31号"};for(int i=0;i<12;i++){if((cal.get(Calendar.MONTH)+1)==i){System.out.println(str[i-1]);}}if(Calendar.MONTH==5){cal.set(Calendar.DAY_OF_MONTH, cal.getActualMaximum(Calendar.DAY_OF_MONTH));SimpleDateFormat simpleDateFormat = new SimpleDateFormat( "yyyy-MM-dd ");simpleDateFormat.format(cal.getTime());//输出2005-04-30System.out.println("现在的时间是："+simpleDateFormat.format(cal.getTime()));}}}package com.java.page;import java.text.SimpleDateFormat;import java.util.Calendar;import java.util.Date;import java.util.GregorianCalendar;public class Student {public static void main(String args[])throws Exception{//Calendar cal=Calendar.getInstance();//cal.set(Calendar.MONTH, 6);//cal.set(Calendar.DAY_OF_MONTH, cal.getActualMaximum(Calendar.DAY_OF_MONTH));//System.out.println(cal.getTime());System.out.println(getLastDay());System.out.println(getLastDayOfLastMonth());System.out.println("---------"+ss());System.out.println("=========="+sd());}public static String getLastDay(){SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd"); Calendar calendar = Calendar.getInstance();//此时打印它获取的是系统当前时间 calendar.add(Calendar.DATE, -1); // Date theDate = calendar.getTime(); String s = df.format(theDate); System.out.println(s); return s;}public static Date getLastDayOfLastMonth() {Calendar calendar = new GregorianCalendar();calendar.set(Calendar.DATE, 1);calendar.set(Calendar.HOUR, 0);calendar.set(Calendar.MINUTE, 0);calendar.set(Calendar.SECOND, 0);calendar.set(Calendar.MILLISECOND, 0);long mils = calendar.getTime().getTime();mils -= 24 * 60 * 60 * 1000;return new Date(mils);}public static String ss(){Calendar cal=Calendar.getInstance();//当前日期cal.set(Calendar.DATE,1);//设为当前月的1号cal.add(Calendar.DATE,-1);//减一天，变为上月最后一天SimpleDateFormat simpleDateFormat = new SimpleDateFormat( "yyyy-MM-dd ");return simpleDateFormat.format(cal.getTime());//输出2005-04-30}public static String sd(){//Calendar cal=Calendar.getInstance();Calendar cal=new GregorianCalendar(2000,2,1);cal.add(Calendar.MONTH,-1);return "2000年3月1号的上个月份最后一天是 "+cal.getActualMaximum(Calendar.DAY_OF_MONTH);}}package com.java.page;import java.text.SimpleDateFormat;import java.util.Calendar;public class Hello {public static void main(String args[]){Calendar cal=Calendar.getInstance();System.out.println(cal.get(Calendar.YEAR)+"年");System.out.println(cal.get(Calendar.MONTH)+1+"月");System.out.println(cal.get(Calendar.DATE)+"日");System.out.println("<br/>");java.util.Date date=new java.util.Date();SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM");String nowm=sdf.format(date);System.out.println("现在的时间是："+nowm);}}