IO案例

import java.io.File;import java.io.FileNotFoundException;import java.io.FileWriter;import java.io.IOException;import java.util.ArrayList;import java.util.Scanner;//查找D盘下是否存在number.txt文件，如果没有则创建；//如有则提示用户输入10个字符串，以追加的方式写入到number.txt中public class FindFileDemo {private static ArrayList<File> file =new ArrayList<>();private static File newfile;//在area中查找target文件public static void FindFile(File area,String target){if(area.isDirectory()){File[] fs = area.listFiles();if(fs != null){   //何时fs ==null？for(File f: fs){if(f.getName().equals(target)){file.add(f);//System.out.println(f);}else{FindFile(f,target);}}}}}public static void main(String[] args) throws FileNotFoundException {String target = new String("number.txt");File area = new File("E:/");FindFile(area,target);if(!file.isEmpty()){System.out.println(file);newfile = file.get(0);}else{newfile = new File(area,target);System.out.println("文件不存在，现在创建"+newfile);try {newfile.createNewFile();} catch (IOException e) {e.printStackTrace();}}System.out.println("请输入10个字符串：");Scanner in = new Scanner(System.in);String str = new String();for(int i=0; i<10; i++){str += (in.nextLine());}in.close();try {FileWriter write = new FileWriter(newfile,true);write.write(str,0,str.length());write.close();} catch (IOException e) {e.printStackTrace();}}}