【209天】黑马程序员27天视频学习笔记【Day21-下】_ios教程

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【209天】黑马程序员27天视频学习笔记【Day21-下】

发布时间：2019-06-30 发布网站：脚本宝典

脚本宝典收集整理的这篇文章主要介绍了【209天】黑马程序员27天视频学习笔记【Day21-下】，脚本宝典觉得挺不错的，现在分享给大家，也给大家做个参考。

叨逼叨两句
想做NB程序员，还是不要喝酒为妙。
21-（12-13）:使用指定码表读写字符+转换流图解

每个文件都有对应的编码，若你用不同的编码表去读取文件，就会乱码。
字符流FileReader、FileWrITer都采用默认编码表。直接用来读取文件内容，会用默认编码表进行转换，不成功，写出的文件就乱码，所以还是用字节流FileinputStream读取后再用IputStreamReader转换合适。FileWriter同理。

InputStreamReader：字节流通向字符流
OutputStreamReader：字符流通向字节流

若不指定编码表，则为平台默认编码表。

      
      
      
      
      
package com.test.demo001;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;

public class Demo009 {
    public static void main(String[] args) throws IOException{
        //demo01();
        InputStreamReader isr = new InputStreamReader(new FileInputStream("utf-8.txt"),"utf-8"); 
        OutputStreamWriter osr = new OutputStreamWriter(new FileOutputStream("GBK.txt"),"gbk");
        int c;
        while((c = isr.read())!= -1){
            osr.write(c);
        }
        isr.close();
        osr.close();
        
    }

    PRivate static void demo01() throws FileNotFoundException, IOException {
        FileReader fr = new FileReader("GBK.txt");
        FileWriter fw = new FileWriter("US-ASCII.txt");
        int c;
        while((c = fr.read())!= -1){
            fw.write(c);
        }
        
        fr.close();
        fw.close();
    }
}


加上缓冲

      
      
      
      
      
package com.test.demo001;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.UnsupportedEncodingException;

public class Demo009 {
    public static void main(String[] args) throws IOException{
        //demo01();
        //demo02();
        BufferedReader br = 
                new BufferedReader(new InputStreamReader(new FileInputStream("utf-8.txt"),"utf-8"));
        BufferedWriter bw = 
                new BufferedWriter(new OutputStreamWriter(new FileOutputStream("GBK.txt"),"gbk"));

        int c;
        while((c = br.read())!= -1){
            bw.write(c);
        }
        br.close();
        bw.close();
    }

    private static void demo02() throws UnsupportedEncodingException, FileNotFoundException, IOException {
        InputStreamReader isr = new InputStreamReader(new FileInputStream("utf-8.txt"),"utf-8");
        OutputStreamWriter osr = new OutputStreamWriter(new FileOutputStream("GBK.txt"),"gbk");
        int c;
        while((c = isr.read())!= -1){
            osr.write(c);
        }
        isr.close();
        osr.close();
    }

    private static void demo01() throws FileNotFoundException, IOException {
        FileReader fr = new FileReader("GBK.txt");
        FileWriter fw = new FileWriter("US-ASCII.txt");
        int c;
        while((c = fr.read())!= -1){
            fw.write(c);
        }
        
        fr.close();
        fw.close();
    }
}


21-14:获取文本上字符出现的次数

      
      
      PE="button" class="copyCode code-tool" data-toggle="tooltip" data-placement="top" data-clipboard-text="package com.test.demo001;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.TreeMap;

public class Demo009 {
    public static void main(String[] args) throws IOException{
        BufferedReader br = new BufferedReader(new FileReader("b.txt"));
        TreeMap tm = new TreeMap<>();
        int ch;
        while((ch = br.read())!= -1){
            char c = (char)ch;
            /*if(!tm.containsKey(c)){
                tm.put(c, 1);
            } else {
                tm.put(c, tm.get(c)+1);
            }*/
            tm.put(c, !tm.containsKey(c)? 1:tm.get(c)+1);
            }    
            br.close();
            BufferedWriter bw = new BufferedWriter(new FileWriter("times.txt"));
            for (Character key : tm.keySet()) {
                
                switch(key){
                case 't':
                    bw.write("\t" + "=" + tm.get(key));
                    break;
                case 'n':
                    bw.write("\n" + "=" + tm.get(key));
                    break;
                case 'r':
                    bw.write("\r" + "=" + tm.get(key));
                    break;
                default:
                    bw.write(key + "=" + tm.get(key));
                    break;
                }
                bw.newLine();
            }
            bw.close();
    }
}" title="" data-original-title="复制">
      
      
package com.test.demo001;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.TreeMap;

public class Demo009 {
    public static void main(String[] args) throws IOException{
        BufferedReader br = new BufferedReader(new FileReader("b.txt"));
        TreeMap<Character,Integer> tm = new TreeMap<>();
        int ch;
        while((ch = br.read())!= -1){
            char c = (char)ch;
            /*if(!tm.containsKey(c)){
                tm.put(c, 1);
            } else {
                tm.put(c, tm.get(c)+1);
            }*/
            tm.put(c, !tm.containsKey(c)? 1:tm.get(c)+1);
            }    
            br.close();
            BufferedWriter bw = new BufferedWriter(new FileWriter("times.txt"));
            for (Character key : tm.keySet()) {
                
                switch(key){
                case 't':
                    bw.write("\t" + "=" + tm.get(key));
                    break;
                case 'n':
                    bw.write("\n" + "=" + tm.get(key));
                    break;
                case 'r':
                    bw.write("\r" + "=" + tm.get(key));
                    break;
                default:
                    bw.write(key + "=" + tm.get(key));
                    break;
                }
                bw.newLine();
            }
            bw.close();
    }
}
21-15:试用版软件

      
      
      System.out.println("您还有" + times-- + "次机会" );
            FileWriter fw = new FileWriter("config.txt");
            fw.write(times + "");
            fw.close();
        } else {
            System.out.println("次数已到");
        } 
        br.close();
    }
}
" title="" data-original-title="复制">
      
      
package com.test.demo001;

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

public class Demo010 {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new FileReader("Config.txt"));
        String line = br.readLine();
        int times = Integer.parseInt(line);
        if(times > 0){
            System.out.println("您还有" + times-- + "次机会" );
            FileWriter fw = new FileWriter("Config.txt");
            fw.write(times + "");
            fw.close();
        } else {
            System.out.println("次数已到");
        } 
        br.close();
    }
}

21-16：递归
递归比较占内存

      
      
      
      
      
public static int fun(int nem)
    if(num == 1){
        return 1;
    }else {
        return num * fun(num - 1)
    }
21-17:递归练习：从键盘输入一个文件夹路径，打印出该文件夹下所有Java文件

      
      
      
      
      
package com.test.demo001;

import java.io.File;
import java.io.IOException;
import java.util.Scanner;

public class Demo010 {
    public static void main(String[] args) throws IOException {
        File dir = getDir();
        printJavaFile(dir);
        
    }

    public static File getDir(){
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入一个文件夹路径");
        while(true){
            String line = sc.nextLine();
            File dir = new File(line);
            if(!dir.exists()){
                System.out.println("您录入的文件夹路径不存在，请重新输入");
            }else if(dir.isFile()){
                System.out.println("您录入的是文件路径，请重新输入文件夹路径");
            }else {
                return dir;
            }
        }
    }
    
    public static void printJavaFile(File dir){
        File[] subFiles = dir.listFiles();
        for (File subFile : subFiles) {
            if(subFile.isFile()&&subFile.getName().endsWith(".jpeg")){
                System.out.println(subFile);
            }else if(subFile.isDirectory()){
                printJavaFile(subFile);
            }
                
        }
    }

}