Java 基础 (IO流练习-图片加解密,字符字数统计)

图片加解密

PicTest.java

package com.klvchen.exer;

import org.junit.Test;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;

public class PicTest {

    //图片加密
    @Test
    public void test1(){
        FileInputStream fis = null;
        FileOutputStream fos = null;
        try {
            fis = new FileInputStream("1.png");
            fos = new FileOutputStream("1secret.jpg");

            byte[] buffer = new byte[20];
            int len;
            while ((len = fis.read(buffer)) != -1) {
                //字节数组进行修改
                //错误的
                //for (byte b : buffer) {
                //    b = (byte) (b ^ 5);
                //}

                //正确的
                for (int i = 0; i < len; i++) {
                    buffer[i] = (byte) (buffer[i] ^ 5);
                }

                fos.write(buffer, 0 ,len);
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if (fos != null)
                    fos.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
            try {
                if (fis != null)
                    fis.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }


    }

    //图片解密
    @Test
    public void test2(){
        FileInputStream fis = null;
        FileOutputStream fos = null;
        try {
            fis = new FileInputStream("1secret.jpg");
            fos = new FileOutputStream("4.png");

            byte[] buffer = new byte[20];
            int len;
            while ((len = fis.read(buffer)) != -1) {
                //字节数组进行修改
                //错误的
                //for (byte b : buffer) {
                //    b = (byte) (b ^ 5);
                //}

                //正确的
                for (int i = 0; i < len; i++) {
                    buffer[i] = (byte) (buffer[i] ^ 5);
                }

                fos.write(buffer, 0 ,len);
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if (fos != null)
                    fos.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
            try {
                if (fis != null)
                    fis.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

统计字符个数

WordCount.java

package com.klvchen.exer;

import org.junit.Test;

import java.io.BufferedWriter;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;

public class WordCount {
    @Test
    public void testWordCount(){
        FileReader fr = null;
        BufferedWriter bw = null;
        try {
            //1.创建Map集合
            Map<Character, Integer> map = new HashMap<>();

            //2.遍历每一个字符，每一个字符出现的次数放到 map 中
            fr = new FileReader("dbcp.txt");
            int c = 0;
            while ((c = fr.read()) != -1) {
                //int 还原 char
                char ch = (char) c;
                //判断 char 是否在 map 中第一次出现
                if (map.get(ch) == null) {
                    map.put(ch, 1);
                } else {
                    map.put(ch, map.get(ch) + 1);
                }
            }

            //3.把map中数据存在文件count.txt
            //3.1 创建 Writer
            bw = new BufferedWriter( new FileWriter("count.txt"));

            //3.2 遍历 map，再写入数据
            Set<Map.Entry<Character, Integer>> entrySet = map.entrySet();
            for (Map.Entry<Character, Integer> entry : entrySet) {
                switch (entry.getKey()) {
                    case ' ':
                        bw.write("空格=" + entry.getValue());
                        break;
                    case '\t':
                        bw.write("tab键=" + entry.getValue());
                        break;
                    case '\r':
                        bw.write("回车=" + entry.getValue());
                        break;
                    case '\n':
                        bw.write("换行=" + entry.getValue());
                        break;
                    default:
                        bw.write(entry.getKey() + "=" + entry.getValue());
                        break;
                }
                bw.newLine();
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if (bw != null)
                    bw.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
            try {
                if (fr != null)
                    fr.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}