java学习55天2020/8/31

import java.io.File;
 import java.io.FileInputStream;
 import java.io.InputStream;
 public class Demo {
     public static void main(String[] args) throws Exception {
         File file = new File("D://测试文件.txt");
         InputStream in = new FileInputStream(file);
         int fileLength = (int) file.length();
         byte b[] = new byte[fileLength];
         in.read(b);
         in.close();
         System.out.println("读取的内容是：" + new String(b));
    }
}

　　

import java.io.File;
 import java.io.FileOutputStream;
 import java.io.OutputStream;
 public class Demo {
     public static void main(String[] args) throws Exception {
         File file = new File("D://测试文件.txt");
         OutputStream out=new FileOutputStream(file);
         String str="Java你好！";
         byte b[]=str.getBytes();
        out.write(b);
         out.close();
    }
 }