常用方法归档-获取<日期、字符串倒写、随机数、读写文件>

                //两种日期格式SimpleDateFormat dateFormat=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss E");System.out.println(dateFormat.format(new Date()));SimpleDateFormat dateFormat1=new SimpleDateFormat("yyyy年MM年dd日 HH时:mm分:ss秒 E");System.out.println(dateFormat1.format(new Date()));//字符串倒写StringBuffer buffer=new StringBuffer("我爱中国共产党");buffer.reverse();System.out.println(buffer);//获取当前月最后一天当前日期Calendar calendar=Calendar.getInstance();calendar.set(Calendar.DAY_OF_MONTH,calendar.getActualMaximum(Calendar.DAY_OF_MONTH));Date date=new Date(calendar.getTimeInMillis());System.out.println(dateFormat1.format(date));//生成随机数Random random=new Random();int num=10000;//从<10000中随机选取10个数List list=new ArrayList();for (int i = 0; i < 10; i++) {list.add(random.nextInt(num));}Collections.sort(list);//排序输出for (int i = 0; i < list.size(); i++) {System.out.println(list.get(i));}//读写某磁盘的所有文件File file=new File("E:\\学习文档");File [] files=file.listFiles();for (int i = 0; i < files.length; i++) {if(files[i].isFile()){System.out.println(files[i]);}}//读写某磁盘的所有文件目录for (int i = 0; i < files.length; i++) {if(files[i].isDirectory()){System.out.println(files[i]);}}//判断某个文件是否存在此文件夹下System.out.println(new File("E:\\学习文档\\记录卡功能概括.txt").exists());//读文件FileInputStream inputStream = new FileInputStream("E:\\学习文档\\记录卡功能概括.txt");byte [] bs=new byte[100];while (true) {int len=inputStream.read(bs);if(len<=0)break;System.out.println(new String(bs,0,len));}inputStream.close();//写文件FileWriter fileWriter=new FileWriter("E:\\test.txt");fileWriter.write("你好"+System.getProperty("line.separator"));fileWriter.write("hello,welcome to BeiJing");fileWriter.close();