簡單瞭解IO流：https://www.cnblogs.com/weibanggang/p/10034325.html

package com.wbg.iodemo1128;

import java.io.*;

public class OutputStreamDemo {
    public static void main(String[] args) throws IOException {
        reader();
    }
    //輸入位元組流OutputStream
    static void inputStream() throws IOException {
        File f
 
=new File("F:"+File.separator+"test01.txt");
        InputStream inputStream=new FileInputStream(f);
        byte b[]=new byte[1024];
        inputStream.read(b);
        inputStream.close();
        System.out.println(new String(b));
    }
    //輸出位元組流OutputStream
    static void outputStream()throws IOException{
        
 
//第一步：使用File找到一個檔案
        File f=new File("F:"+File.separator+"test01.txt");
        //建立檔案
        f.createNewFile();
        //第二步：通過子類例項化父類物件
        OutputStream out=new FileOutputStream(f);
        //第三步：寫一個字串
        String str="Hello World!!!";
        //第四步：字串轉為byte陣列
        byte b[]=str.getBytes();
        
 
//第五步：內容輸出
        out.write(b);
        //第六步：關閉
        out.close();
    }
    //字元流輸出
    static void writer() throws IOException {
        //第一步：使用File找到一個檔案
        File f=new File("f:"+File.separator+"test.txt");
        //第二步：通過子類例項化父類物件
        Writer out=new FileWriter(f);
        //追加
       // Writer out=new FileWriter(f,true);
        //第三：定義字串
        String str="Hello,Word!!!";
        //第四步:輸出
        out.write(str);
        //第五步：強制清空快取
        out.flush();
        //第六步：關閉
         out.close();
    }
    //字元流正常輸入
    static void reader() throws IOException {
        //第一步：使用File找到一個檔案
        File f=new File("f:"+File.separator+"test.txt");
        Reader readerout=new FileReader(f);
        int len=0;
        char[]c=new char[1024];
        int temp=0;
        while ((temp=readerout.read())!=-1){
            c[len]=(char)temp;
            len++;
        }
        readerout.close();
        System.out.println(new String(c,0,len));
    }
    //字元流輸入追加
    static void readerAdd() throws IOException {
        File f=new File("f:"+File.separator+"test.txt");
        Reader reader=new FileReader(f);
        char[]c=new char[(int)f.length()];
        reader.read(c);
        reader.close();
        System.out.println(new String(c));
    }
}