java===java基础学习（5）---文件读取，写入操作

文件的写入读取有很多方法，今天学到的是Scanner和PrintWriter

文件读取

Scanner in = new Scanner(Paths.get("file.txt"))

文件写入

PrintWriter out = new PrintWriter("file.txt")

• 文件读取的我目前只发现他是一行一行的读取不能整篇幅的读取，所以写了一个while循环，一行行的打印。
• 文件写入，写入的文件不能实现追加模式的写入。会把之前内容覆盖掉。
• 文件操作完，记得进行close()。

//Scanner文本文件读取与处理
package testbotoo;

import java.io.IOException;
import java.io.PrintWriter;
import java.nio.file.Paths;
import java.util.Scanner;


public class file {
    public static void main(String[] arg) throws IOException{
        //文件读取
        Scanner in = new Scanner(Paths.get("C:\Users\...\Desktop\myfile.txt")); //读取文件操作
        while(in.hasNextLine()){
            String str = in.nextLine();
            if(str.equals("9999")){
                break;
            };
            System.out.println(str);
        }
        in.close();
        //文件写入
        PrintWriter out = new PrintWriter("C:\Users\...\Desktop\myfile.txt");
        out.println("ssss");
        out.println("5466555");
        out.close();
    }
    

}

由于不能写追加写入，又找到了一种新的解决办法：

    import java.util.*;
    import java.io.*;
    public class T {
        public static void main(String[] args) {
            String fileName = "data.txt";
            FileWriter fw = null;
            PrintWriter toFile = null;
            try {
                fw = new FileWriter(fileName, true); //  throw IOException
                toFile = new PrintWriter(fw); // throw FileNotFoundException
            } catch (FileNotFoundException e) {
                System.out.println("PrintWriter error opening the file " + fileName);
                System.exit(0);
            } catch (IOException e) {
                System.out.println("FileWriter error opening the file " + fileName);
                System.exit(0); 
            } 
            System.out.println("Enter four lines of text:");
            Scanner keyboard = new Scanner(System.in);
            for (int count = 1; count <= 4; count++) {
                String line = keyboard.nextLine();
                toFile.println(count + " " + line);
            } 
            System.out.println("Four lines were written to " + fileName);
            toFile.close();
        }
    }