Java 基础之File类

文件的创建与删除：

import java.io.File;
import java.io.IOException;

public class FileTest {

    public static void main(String[] args)
    {
        //创建方法1
        //File file=new File("/Users/yuwenqing/Desktop","hello.txt");

        //创建方法2
        //File file=new File("/Users/yuwenqing/Desktop/hello.txt");


        //创建方法3
        File parentfile=new File("/Users/yuwenqing/Desktop");
        File file=new File(parentfile,"hello.txt");

        if(!file.exists())
        {
            try {
                file.createNewFile();
            } catch (IOException e) {
                e.printStackTrace();
            }
            System.out.println("文件创建成功");
        }
        else
        {
            file.delete();
            System.out.println("文件已删除");
        }

    }
}

运行结果

获取文件信息

常用函数如下：

案例：

import java.io.File;
import java.io.IOException;

public class FileTest {

    public static void main(String[] args)
    {
        //创建方法1
        //File file=new File("/Users/yuwenqing/Desktop","hello.txt");

        //创建方法2
        //File file=new File("/Users/yuwenqing/Desktop/hello.txt");


        //创建方法3
        File parentfile=new File("/Users/yuwenqing/Desktop");
        File file=new File(parentfile,"hello.txt");

        if(file.exists())
        {
            System.out.println("文件名："+file.getName());
            System.out.println("是否可读："+file.canRead());
            System.out.println("是否可写："+file.canWrite());
            System.out.println("是否存在："+file.exists());
            System.out.println("文件长度："+file.length());
            System.out.println("文件绝对路径："+file.getAbsolutePath());
            System.out.println("父路径："+file.getParent());
            System.out.println("是否目录："+file.isDirectory());
            System.out.println("是否隐藏文件："+file.isHidden());
            System.out.println("最后修改时间："+file.lastModified());
        }
        else
        {
            System.out.println("文件不存在");
        }

    }
}

运行结果：

FileOutputStream和FileInputStream 基于字节流

案例：

import java.io.*;

public class FileTest {

    public static void main(String[] args)
    {

        File parentfile=new File("/Users/yuwenqing/Desktop");
        File file=new File(parentfile,"hello.txt");

        try {
            FileOutputStream fileOutputStream=new FileOutputStream(file);
            byte[] bytes="我有一只小毛驴，我从来也不骑".getBytes();
            fileOutputStream.write(bytes);
            fileOutputStream.flush();
            fileOutputStream.close();


            FileInputStream fileInputStream=new FileInputStream(file);
            byte[] newbytes=new byte[1024];
            int len=fileInputStream.read(newbytes);
            System.out.println("输出的信息是："+new String(newbytes,0,len));
            fileInputStream.close();

        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

运行结果：

上面是基于字节流的文件读写，但是读取汉字的时候可能会出现乱码的情况，而接下来要讲的FileReader和FileWriter是基于字符流的，可以避免上述问题

案例：

import java.io.*;

public class FileTest {

    public static void main(String[] args)
    {

        File parentfile=new File("/Users/yuwenqing/Desktop");
        File file=new File(parentfile,"hello.txt");

        try {
            FileWriter fileWriter=new FileWriter(file);
            String s="我有一只小毛驴，从来也不骑";
            fileWriter.write(s);
            fileWriter.close();


            FileReader fileReader=new FileReader(file);
            char[] byt=new char[1024];
            int len=fileReader.read(byt);
            System.out.println("读取的内容是："+new String(byt,0,len));
            fileReader.close();


        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

运行结果：

BufferedReader和BufferedWriter  带有缓冲区的文件读写

案例

import java.io.*;

public class FileTest {

    public static void main(String[] args)
    {

        File parentfile=new File("/Users/yuwenqing/Desktop");
        File file=new File(parentfile,"hello.txt");

        try {
            FileWriter fileWriter=new FileWriter(file);
            BufferedWriter bufferedWriter=new BufferedWriter(fileWriter);
            String[] s={"apple","orange","watermelon","grape"};

            for(int i=0;i<s.length;i++)
            {
                bufferedWriter.write(s[i]);
                bufferedWriter.newLine();
            }

            bufferedWriter.flush();
            bufferedWriter.close();
            fileWriter.close();


            FileReader fileReader=new FileReader(file);
            BufferedReader bufferedReader=new BufferedReader(fileReader);

            int i=1;
            String s1=null;
            while ((s1=bufferedReader.readLine())!=null)
            {
                System.out.printf("\n第%d行:"+s1,i);
                i++;
            }
            fileReader.close();
            bufferedReader.close();


        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

运行结果：