Java入门——day55

一、字节输入、输出流

1.InputStream读取文件

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));
    }
}

2.OutputStream写入文件

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();
    }
}

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 二、字符输入、输出流

1.Reader读取文件

一起读取：

import java.io.File;
import java.io.FileReader;
import java.io.Reader;
public class Demo {
    public static void main(String[] args) throws Exception {
        File file = new File("D://测试文件.txt");
        Reader reader=new FileReader(file);
        char c[]=new char[1024]; //字符数组
        int len=reader.read(c);
        reader.close();
        System.out.println("读取的内容是："+new String(c,0,len));
    }
}

 逐个读取：

import java.io.File;
import java.io.FileReader;
import java.io.Reader;
public class Demo {
    public static void main(String[] args) throws Exception {
        File file = new File("D://测试文件.txt");
        Reader reader=new FileReader(file);
        char c[]=new char[1024]; //字符数组
        int temp=0;
        int len=0;
        while((temp=reader.read())!=-1) {
            c[len++]=(char)temp;
        }
        reader.close();
        System.out.println("读取的内容是："+new String(c,0,len));
    }
}

2.Writer写入文件

以覆盖的形式：

import java.io.File;
import java.io.FileWriter;
import java.io.Writer;
public class Demo {
    public static void main(String[] args) throws Exception {
        File file = new File("D://测试文件.txt");
        Writer out=new FileWriter(file);
        String str="我爱Java";
        out.write(str);  //将字符串写入输出流
        out.close();
    }
}

 以追加的形式：

import java.io.File;
import java.io.FileWriter;
import java.io.Writer;
public class Demo {
    public static void main(String[] args) throws Exception {
        File file = new File("D://测试文件.txt");
        Writer out=new FileWriter(file,true);
        String str="，你也爱Java";
        out.write(str);  //将字符串写入输出流
        out.close();
    }
}