ArrayList与HashMap的嵌套使用

  1. /*
  2.         ArrayList与HashMap的嵌套使用
  3.      */
  4.     public static void main(String[] args) {
  5.         ArrayList<HashMap<String,String>> array = new ArrayList<>();
  6.         HashMap<String,String> hm1 = new HashMap<>();
  7.         hm1.put("孙策","大乔");
  8.         hm1.put("周瑜","小乔");
  9.         array.add(hm1);
  11.         HashMap<String,String> hm2 = new HashMap<>();
  12.         hm1.put("孙策1","大乔1");
  13.         hm1.put("周瑜1","小乔1");
  14.         array.add(hm2);
  16.         HashMap<String,String> hm3 = new HashMap<>();
  17.         hm1.put("孙策2","大乔2");
  18.         hm1.put("周瑜2","小乔2");
  19.         array.add(hm3);
  20.         for (HashMap<String,String> hm:array){
  21.             for (String key:hm.keySet()){
  22.                 System.out.println(key+","+hm.get(key));
  23.             }
  24.         }
  25.     }

孙策2,大乔2 孙策1,大乔1 周瑜2,小乔2 孙策,大乔 周瑜1,小乔1 周瑜,小乔

Process finished with exit code 0

  1. /*
  2.         ArrayList与HashMap的嵌套使用
  3.      */
  4.     public static void main(String[] args) {
  5.         HashMap<String,ArrayList<String>> hm = new HashMap<>();
  6.         ArrayList<String> array1 = new ArrayList<>();
  7.         array1.add("诸葛");
  8.         array1.add("刘备");
  9.         hm.put("三国",array1);
  11.         ArrayList<String> array2 = new ArrayList<>();
  12.         array2.add("八戒");
  13.         array2.add("悟空");
  14.         hm.put("西游",array2);
  16.         ArrayList<String> array3 = new ArrayList<>();
  17.         array3.add("宋飞");
  18.         array3.add("武松");
  19.         hm.put("水浒",array3);
  21.         for (String s:hm.keySet()){
  22.             System.out.print(s+":");
  23.             for (String array:hm.get(s)){
  24.                 System.out.print(array+"、");
  25.             }
  26.             System.out.println("\n");
  27.         }
  28.     }

水浒:宋飞、武松、

西游:八戒、悟空、

三国:诸葛、刘备、

Process finished with exit code 0

统计字符出现次数

hashmap 键值应为包装类
使用TreeMap可使结果有序

  1. /*
  2.         统计字符串中各个字母出现的次数
  3.      */
  4.     public static void main(String[] args) {
  5.         Scanner sc = new Scanner(System.in);
  6.         System.out.print("请输入字符串:");
  7.         String line = sc.nextLine();
  9.         TreeMap<Character, Integer> hm = new TreeMap<>();
  11.         for (int i = 0; i < line.length(); i++) {
  12.             char key = line.charAt(i);
  13.             Integer value = hm.get(key);
  14.             //先判断键 是否存在
  15.             if (value == null){
  16.                 hm.put(key,1);
  17.             }else{
  18.                 value++;
  19.                 hm.put(key,value);
  20.             }
  21.         }
  22.         StringBuffer sb = new StringBuffer();
  23.         Set<Character> keySet = hm.keySet();
  24.         for (Character key:keySet){
  25.             Integer value = hm.get(key);
  26.             sb.append(key).append("("+value+")");
  27.         }
  28.         String res = sb.toString();
  29.         System.out.println(res);
  30.     }

请输入字符串:bdacegf a(1)b(1)c(1)d(1)e(1)f(1)g(1)

Process finished with exit code 0

Collections 类

对集合操作的工具类
image.png

  1. public static void main(String[] args) {
  2.         List<Integer> list = new ArrayList<>();
  3.         list.add(30);
  4.         list.add(10);
  5.         list.add(40);
  6.         list.add(50);
  7.         list.add(20);
  8.         //排序
  9.         Collections.sort(list);
  10.         System.out.println(list);
  11.         //[10, 20, 30, 40, 50]
  13.         //反转
  14.         Collections.reverse(list);
  15.         System.out.println(list);
  16.         //[50, 40, 30, 20, 10]
  18.         //随机排序
  19.         Collections.shuffle(list);
  20.         System.out.println(list);
  21.         //[20, 40, 50, 30, 10]
  22.     }

排序

  1. public class Teacher {
  2.     private String name;
  3.     private int age;
  5.     public Teacher() {
  6.     }
  8.     public Teacher(String name, int age) {
  9.         this.name = name;
  10.         this.age = age;
  11.     }
  13.     @Override
  14.     public String toString() {
  15.         return "Teacher{" +
  16.                 "name='" + name + '\'' +
  17.                 ", age=" + age +
  18.                 '}';
  19.     }
  21.     @Override
  22.     public boolean equals(Object o) {
  23.         if (this == o) return true;
  24.         if (o == null || getClass() != o.getClass()) return false;
  26.         Teacher teacher = (Teacher) o;
  28.         if (age != teacher.age) return false;
  29.         return name != null ? name.equals(teacher.name) : teacher.name == null;
  30.     }
  32.     @Override
  33.     public int hashCode() {
  34.         int result = name != null ? name.hashCode() : 0;
  35.         result = 31 * result + age;
  36.         return result;
  37.     }
  39.     public String getName() {
  40.         return name;
  41.     }
  43.     public void setName(String name) {
  44.         this.name = name;
  45.     }
  47.     public int getAge() {
  48.         return age;
  49.     }
  51.     public void setAge(int age) {
  52.         this.age = age;
  53.     }
  55. }

创建匿名内部类排序

  1. public static void main(String[] args) {
  3.         ArrayList<Teacher> ts = new ArrayList<>();
  4.         Teacher s1 = new Teacher("张三", 40);
  5.         Teacher s2 = new Teacher("李四", 30);
  6.         Teacher s3 = new Teacher("王五", 10);
  7.         Teacher s4 = new Teacher("李四", 20);
  8.         //Teacher s5 = new Teacher("m四", 20);
  10.         ts.add(s1);
  11.         ts.add(s2);
  12.         ts.add(s3);
  13.         ts.add(s4);
  14.         //set.add(s5);
  16.         //创建匿名内部类排序
  17.         Collections.sort(ts, new Comparator<Teacher>() {
  18.             @Override
  19.             public int compare(Teacher s1, Teacher s2) {
  20.                 int num = s1.getAge() - s2.getAge();  //age升序
  21.                 //如年龄相同,比较名字
  22.                 int num2 = num == 0?s1.getName().compareTo(s2.getName()):num;
  23.                 return num2;
  24.             }
  25.         });
  27.         for (Teacher t:ts){
  28.             System.out.println(t.getName()+","+t.getAge());
  29.         }
  30.     }

模拟斗地主

  1. /*
  2.         模拟斗地主
  3.      */
  4.     public static void main(String[] args) {
  5.         //定义花色
  6.         String[] colors = {"♥","♠","♦","♣"};
  7.         String[] numbers = {"2","3","4","5","6","7","8","9","10","J","Q","K","A"};
  8.         ArrayList<String> array = new ArrayList<>();
  9.         for (String color:colors){
  10.             for (String number:numbers){
  11.                 array.add(color+number);
  12.             }
  13.         }
  14.         array.add("大王");
  15.         array.add("小王");
  16.         //洗牌
  17.         Collections.shuffle(array);
  18.         //System.out.println(array);
  19.         //发牌
  20.         ArrayList<String> player1 = new ArrayList<>();
  21.         ArrayList<String> player2 = new ArrayList<>();
  22.         ArrayList<String> player3 = new ArrayList<>();
  23.         ArrayList<String> less = new ArrayList<>();
  25.         for (int i = 0;i<array.size();i++){
  26.             String poker = array.get(i);
  27.             if (i>=array.size()-3){
  28.                 less.add(poker);
  29.             }else if (i%3==0){
  30.                 player1.add(poker);
  31.             }else if (i%3==1){
  32.                 player2.add(poker);
  33.             }else if (i%3==2){
  34.                 player3.add(poker);
  35.             }
  36.         }
  37.         showPoker("张三",player1);
  38.         showPoker("李四",player2);
  39.         showPoker("王五",player3);
  40.         showPoker("底牌",less);
  41.     }
  43.     public static void showPoker(String name,ArrayList<String> array){
  44.         System.out.print(name+":");
  45.         for (String s:array){
  46.             System.out.print(s+" ");
  47.         }
  48.         System.out.println();
  49.     }

张三:♦A ♠5 ♣7 ♣K ♣3 ♣9 ♦Q ♣2 小王 ♦K ♠3 ♦6 ♦8 ♥5 ♦10 ♠7 ♦4 李四:♠2 ♥A ♥8 ♥10 ♣A ♥6 ♣6 ♣J ♥Q ♠8 ♠J ♠9 ♥2 ♠Q ♥7 ♣8 ♠A 王五:♥3 ♣4 ♣10 ♥9 ♦5 ♠10 ♥4 ♦9 ♥K ♠4 ♠6 ♣Q ♥J ♦7 大王 ♠K ♦2 底牌:♣5 ♦J ♦3

对扑克排序

  2. public class Demo {
  3.     /*
  4.         模拟斗地主
  5.      */
  6.     public static void main(String[] args) {
  7.         //定义花色
  8.         String[] colors = {"♥", "♠", "♦", "♣"};
  9.         String[] numbers = {"2", "3", "4", "5", "6", "7", "8", "9", "10", "J", "Q", "K", "A"};
  11.         //对扑克按序 排列
  12.         //根据序列获取对应扑克
  13.         HashMap<Integer, String> hm = new HashMap<>();
  14.         ArrayList<Integer> array = new ArrayList<>();
  15.         int index = 1;
  16.         for (String number : numbers) {
  17.             for (String color : colors) {
  18.                 array.add(index);
  19.                 hm.put(index++, color + number);
  20.             }
  21.         }
  22.         array.add(index);
  23.         hm.put(index++, "♚");  //小王
  24.         array.add(index);
  25.         hm.put(index++, "♕");  //大王
  26.         System.out.println(array);  //序列
  27.         /*
  28.                 [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17,
  29.                  18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34,
  30.                  35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51,
  31.                  52, 53, 54]
  32.         */
  33.         System.out.println(hm);  //扑克
  34.         /*
  35.                 {1=♥2, 2=♠2, 3=♦2, 4=♣2, 5=♥3, 6=♠3, 7=♦3, 8=♣3, 9=♥4, 10=♠4,
  36.                 11=♦4, 12=♣4, 13=♥5, 14=♠5, 15=♦5, 16=♣5, 17=♥6, 18=♠6, 19=♦6, 20=♣6,
  37.                 21=♥7, 22=♠7, 23=♦7, 24=♣7, 25=♥8, 26=♠8, 27=♦8, 28=♣8, 29=♥9, 30=♠9,
  38.                 31=♦9, 32=♣9, 33=♥10, 34=♠10, 35=♦10, 36=♣10, 37=♥J, 38=♠J, 39=♦J, 40=♣J,
  39.                 41=♥Q, 42=♠Q, 43=♦Q, 44=♣Q, 45=♥K, 46=♠K, 47=♦K, 48=♣K, 49=♥A, 50=♠A,
  40.                 51=♦A, 52=♣A, 53=小王, 54=大王}
  41.         */
  42.         //洗牌  -->打乱序号
  43.         Collections.shuffle(array);
  44.         //System.out.println(array);
  46.         //发牌 使用TreeSet集合存储序列,使之有序
  47.         TreeSet<Integer> player1 = new TreeSet<>();
  48.         TreeSet<Integer> player2 = new TreeSet<>();
  49.         TreeSet<Integer> player3 = new TreeSet<>();
  50.         TreeSet<Integer> less = new TreeSet<>();
  51.         //发牌 -->实际分发的是序号,最后根据序号,得到属于自己的牌
  52.         for (int i = 0;i<array.size();i++){
  53.             Integer poker = array.get(i);
  54.             if (i>=array.size()-3){
  55.                 less.add(poker);
  56.             }else if (i%3==0){
  57.                 player1.add(poker);
  58.             }else if (i%3==1){
  59.                 player2.add(poker);
  60.             }else if (i%3==2){
  61.                 player3.add(poker);
  62.             }
  63.         }
  64.         showPoker("张三",player1,hm);
  65.         showPoker("李四",player2,hm);
  66.         showPoker("王五",player3,hm);
  67.         showPoker("底牌",less,hm);
  68.     }
  70.     public static void showPoker(String name, TreeSet<Integer> array,HashMap<Integer,String> hm) {
  71.         System.out.print(name + ":");
  72.         for (Integer key : array) {
  73.             System.out.print(hm.get(key)+" ");
  74.         }
  75.         System.out.println();  //换行
  76.     }
  77. }

张三:♣2 ♠3 ♦3 ♣3 ♥4 ♥5 ♠6 ♥7 ♥8 ♠8 ♣8 ♥9 ♣9 ♥10 ♠J ♣K ♦A 李四:♦2 ♥3 ♠4 ♦5 ♦7 ♠10 ♦10 ♣J ♥Q ♠Q ♦Q ♥K ♠K ♦K ♠A ♣A ♕ 王五:♥2 ♠2 ♦4 ♣4 ♠5 ♣5 ♥6 ♦6 ♣6 ♠7 ♣7 ♦8 ♠9 ♦9 ♣Q ♥A ♚ 底牌:♣10 ♥J ♦J

File类

image.png

构造方法

  1.     /*
  2.         File类
  3.      */
  4.     public static void main(String[] args) {
  5.         File f1 = new File("D:\\Java\\test.txt");
  6.         System.out.println(f1);  //D:\Java\test.txt
  7.         File f2 = new File("D:\\Java","test.txt");
  8.         System.out.println(f2);  //D:\Java\test.txt
  9.         File f3 = new File("D:\\Java");
  10.         File f4 = new File(f3,"test.txt");
  11.         System.out.println(f4);  //D:\Java\test.txt
  12.     }

创建文件或文件夹

  1. public static void main(String[] args) throws IOException {
  2.         File f1 = new File("D:\\Java\\test.txt");
  3.         /*
  4.             抛出异常 throws IOException
  5.             如文件不存在,则创建文件,返回true
  6.             文件已存在则返回false
  7.          */
  8.         //System.out.println(f1.createNewFile());
  9.         File f2 = new File("D:\\Java\\test");
  10.         /*
  11.             创建文件夹,不存在-->创建返回true
  12.             存在-->false
  13.          */
  14.         //System.out.println(f2.mkdir());
  15.         File f3 = new File("D:\\Java\\test1\\test");
  16.         /*
  17.             创建多级文件夹,不存在-->创建返回true
  18.             存在-->false
  19.          */
  20.         //System.out.println(f3.mkdirs());
  22.     }

image.png

常用方法

  1. /*
  2.         File类
  3.      */
  4.     public static void main(String[] args) throws IOException {
  5.         File f1 = new File("D:\\Java\\javaFound");
  6.         //是否为目录
  7.         System.out.println(f1.isDirectory());
  8.         //是否为文件
  9.         System.out.println(f1.isFile());
  10.         //是否存在
  11.         System.out.println(f1.exists());
  12.         //获取绝对路径
  13.         System.out.println(f1.getAbsolutePath());
  14.         //获取相对路径
  15.         System.out.println(f1.getPath());
  16.         //获取文件(夹)名
  17.         System.out.println(f1.getName());
  20.         File f = new File("D:\\Java");
  21.         //获取目录下文件列表
  22.         String[] str = f.list();
  23.         for (String s:str){
  24.             System.out.println(s);
  25.         }
  26.         System.out.println("-------------");
  27.         File[] files = f.listFiles();
  28.         for (File file:files){
  29.             if (file.isFile()){  //是否为文件
  30.                 System.out.println(file);  //路径
  31.                 System.out.println(file.getName());  //文件名
  32.             }
  33.         }
  34.     }

true false true D:\Java\javaFound D:\Java\javaFound javaFound 09《Spring Boot企业级开发教材》 12《Java EE企业级应用开发Spring+Sspring MVC+MyBatis》 Java.md javaFound Java笔记.md SpringBoot SpringBoot.md SQL.md

毕业设计.md

D:\Java\Java.md Java.md D:\Java\Java笔记.md Java笔记.md D:\Java\SpringBoot.md SpringBoot.md D:\Java\SQL.md SQL.md D:\Java\毕业设计.md 毕业设计.md

Process finished with exit code 0

  1. public static void main(String[] args) throws IOException {
  2.         File file = new File("test.txt");
  3.         //相对路径创建文件
  4.         //System.out.println(file.createNewFile());
  5.         //删除文件
  6.         System.out.println(file.delete());
  8.         File file1 = new File("src\\content");
  9.         //创建目录(文件夹)
  10.         System.out.println(file1.mkdir());
  11.         //删除目录
  12.         System.out.println(file1.delete());
  13.         //如目录下含有文件,则不能直接删除
  14.     }

递归

  1. public static void main(String[] args) throws IOException {
  2.         System.out.println(rabbit(20));  //6765
  3.         System.out.println(jc(10));  //3628800
  4.     }
  5.     //求斐波那契数列第m项
  6.     public static int rabbit(int m){
  7.         //递归出口
  8.         if (m<3){
  9.             return 1;
  10.         }
  11.         return rabbit(m-1)+rabbit(m-2);
  12.     }
  13.     //求阶乘
  14.     public static int jc(int n){
  15.         if (n==1){
  16.             return 1;
  17.         }
  18.         return n*jc(n-1);
  19.     }

递归遍历文件

  1. /*
  2.         递归
  3.         1.出口
  4.         2.规则
  5.      */
  6.     public static void main(String[] args) throws IOException {
  7.         File f = new File("D:\\Java\\09_《Spring Boot企业级开发教材》");
  8.         fileContent(f);
  9.     }
  11.     //遍历目录下所有文件的绝对路径
  12.     public static void fileContent(File f) {
  13.         File[] files = f.listFiles();
  14.         if (files != null) {
  15.             for (File file : files) {
  16.                 if (file.isDirectory()) {
  17.                     fileContent(file);
  18.                 } else {
  19.                     System.out.println(file.getAbsolutePath());
  20.                 }
  21.             }
  22.         }
  23.     }

D:\Java\09《Spring Boot企业级开发教材》\工具包\apache-maven-3.6.0-bin.zip D:\Java\09《Spring Boot企业级开发教材》\工具包\apache-tomcat-9.0.16.zip D:\Java\09《Spring Boot企业级开发教材》\工具包\jdk-8u201-windows-i586.exe D:\Java\09《Spring Boot企业级开发教材》\工具包\jdk-8u201-windows-x64.exe D:\Java\09《Spring Boot企业级开发教材》\工具包\otp_win64_21.2.exe D:\Java\09《Spring Boot企业级开发教材》\工具包\rabbitmq-server-3.7.9.exe D:\Java\09《Spring Boot企业级开发教材》\工具包\redis-desktop-manager-0.8.8.384.exe D:\Java\09《Spring Boot企业级开发教材》\工具包\Redis-x64-3.2.100.zip D:\Java\09《Spring Boot企业级开发教材》\源代码\Spring Boot教材资源.rar D:\Java\09《Spring Boot企业级开发教材》\源代码\Spring Boot配套源代码.zip D:\Java\09_《Spring Boot企业级开发教材》\课后题答案\SpringBoot教材课后习题答案.doc

Process finished with exit code 0

IO流概述

  • 字节流

  • 字符流

    1. /*
    2.      字节流写入对象
    3.    */
    4.   public static void main(String[] args) throws IOException {
    5.       //文件不存在则创建文件
    6.       FileOutputStream fos = new FileOutputStream("src\\taobao.txt");
    7.       //写入字节
    8.       fos.write(97);  //a
    9.       fos.write(57);  //9
    11.       byte[] bt = {57, 56, 55, 54, 53, 52, 51, 50, 49, 48};
    12.       fos.write(bt);
    14.       byte[] bt1 = "abcde".getBytes();
    15.       fos.write(bt1);  //直接写入 abcde
    17.       //指定长度写入,从索引0开始,长度为3的bt1数组写入
    18.       fos.write(bt1,0,3);
    20.       //释放资源,关闭文件输出流
    21.       fos.close();
    22.   }

    换行

    换行
    window: \r\n
    linux: \n
    mac: \r

    1. /*
    2.      字节流写入,异常处理,使程序更健壮
    3.    */
    4.   public static void main(String[] args) {
    5.       //参数true,表示追加写入,默认false
    6.       FileOutputStream fos = null;
    7.       try {
    8.           fos = new FileOutputStream("src\\taobao.txt", true);
    9.           for (int i = 0; i < 10; i++) {
    10.               fos.write("hello".getBytes());
    11.               fos.write("\r\n".getBytes());   //换行
    12.           }
    13.       } catch (IOException e) {
    14.           e.printStackTrace();
    15.       } finally {
    16.           if (fos != null) {
    17.               try {
    18.                   fos.close();
    19.               } catch (IOException e) {
    20.                   e.printStackTrace();
    21.               }
    22.           }
    23.       }
    24.   }

    读取

    当读到文件内容末位,返回值为-1

    1. public static void main(String[] args) throws IOException {
    2.       //文件不存在则创建文件
    3.       FileInputStream fis = new FileInputStream("src\\taobao.txt");
    4.       //读取一个字节
    5.       int by;
    6.       //当读到文件内容末位,返回值为-1
    7.       while ((by = fis.read()) != -1) {
    8.           System.out.println((char) by);
    9.       }
    11.       //释放资源,关闭文件输出流
    12.       fis.close();
    13.   }

    复制文件内容

    1. public static void main(String[] args) throws IOException {
    2.       //将文件java.md的内容复制到taobao.txt
    3.       FileOutputStream fos = new FileOutputStream("src\\taobao.txt");//写入
    4.       FileInputStream fis = new FileInputStream("D:\\Java\\java.md");  //读取
    5.       //读取一个字节
    6.       int by;
    7.       //当读到文件内容末位,返回值为-1
    8.       while ((by = fis.read()) != -1) {
    9.           fos.write(by);
    10.       }
    11.       //释放资源,关闭文件输出流
    12.       fos.close();
    13.       fis.close();
    14.   }

    读取文件—常用

    1. public static void main(String[] args) throws IOException {
    2.       FileInputStream fis = new FileInputStream("src\\taobao.txt");  //读取
    3.       //读取N个字节
    4.       byte[] by = new byte[1024];
    5.       int len;
    6.       while ((len = fis.read(by)) != -1) {
    7.           System.out.println(new String(by, 0, len));
    8.       }
    9.       //释放资源,关闭文件输出流
    10.       fis.close();
    11.   }

    复制图片

    1. public static void main(String[] args) throws IOException {
    2.       FileOutputStream fos = new FileOutputStream("src\\aac.png");//写入
    3.       FileInputStream fis = new FileInputStream("D:\\Album\\1号线.png");  //读取
    4.       //读取N个字节
    5.       byte[] by = new byte[1024];
    6.       int len;
    7.       while ((len = fis.read(by)) != -1) {
    8.           //System.out.println(new String(by,0,len));
    9.           fos.write(by);
    10.       }
    11.       //释放资源,关闭文件输出流
    12.       fis.close();
    13.       fos.close();
    14.   }

    字节缓冲流 读写数据

    1. /*
    2.  字节缓冲流 读写数据
    3. */
    4. public static void main(String[] args) throws IOException {
    5.   BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream("src\\taobao.txt"));
    6.   bos.write("hello ".getBytes());
    7.   bos.write("world\n".getBytes());
    8.   bos.close();
    10.   BufferedInputStream bis = new BufferedInputStream(new FileInputStream("src\\taobao.txt"));
    11.   byte[] by = new byte[1024];
    12.   int len;
    13.   while ((len = bis.read(by)) != -1) {
    14.       System.out.println(new String(by, 0, len));
    15.   }
    16.   bis.close();
    17. }

    复制视频

    分别以4种方式复制

  • 字节复制

  • 字节数组复制
  • 缓冲流字节复制

  • 缓冲流字节数组复制 ——-最快!!!

    1. public static void main(String[] args) throws IOException {
    2.       long start = System.currentTimeMillis();
    3.       CopyVideo2();
    4.       long end = System.currentTimeMillis();
    5.       System.out.println("耗时:" + (end - start) + "毫秒");
    6.   }
    8.   //耗时:156813毫秒
    9.   public static void CopyVideo() throws IOException {
    10.       //将文件java.md的内容复制到taobao.txt
    11.       FileOutputStream fos = new FileOutputStream("src\\code.mp4");//写入
    12.       FileInputStream fis = new FileInputStream("D:\\草稿\\202104182103.mp4");  //读取
    13.       //读取一个字节
    14.       int by;
    15.       //当读到文件内容末位,返回值为-1
    16.       while ((by = fis.read()) != -1) {
    17.           fos.write(by);
    18.       }
    19.       //释放资源,关闭文件输出流
    20.       fos.close();
    21.       fis.close();
    22.   }
    24.   //耗时:268毫秒
    25.   public static void CopyVideo1() throws IOException {
    26.       //将文件java.md的内容复制到taobao.txt
    27.       FileOutputStream fos = new FileOutputStream("src\\code.mp4");//写入
    28.       FileInputStream fis = new FileInputStream("D:\\草稿\\202104182103.mp4");  //读取
    29.       //读取一个字节
    30.       byte[] by = new byte[1024];
    31.       int len;
    32.       while ((len = fis.read(by)) != -1) {
    33.           fos.write(by);
    34.       }
    35.       //释放资源,关闭文件输出流
    36.       fos.close();
    37.       fis.close();
    38.   }
    40.   //耗时:1244毫秒
    41.   public static void CopyVideo2() throws IOException {
    42.       BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream("src\\code.mp4"));
    43.       BufferedInputStream bis = new BufferedInputStream(new FileInputStream("D:\\草稿\\202104182103.mp4"));
    44.       //读取一个字节
    45.       int by;
    46.       //当读到文件内容末位,返回值为-1
    47.       while ((by = bis.read()) != -1) {
    48.           bos.write(by);
    49.       }
    50.       bos.close();
    51.       bis.close();
    52.   }
    54.   //耗时:95毫秒
    55.   public static void CopyVideo3() throws IOException {
    56.       BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream("src\\code.mp4"));
    57.       BufferedInputStream bis = new BufferedInputStream(new FileInputStream("D:\\草稿\\202104182103.mp4"));
    58.       byte[] by = new byte[1024];
    59.       int len;
    60.       while ((len = bis.read(by)) != -1) {
    61.           bos.write(by);
    62.       }
    63.       bos.close();
    64.       bis.close();
    65.   }

    字符流—编码-解码

    ```java

    1.    //String s = "abc";  //[97,98,99]
    2.   String s = "中国";

    //相同,说明默认采用utf-8编码

    1.   //byte[] bys = s.getBytes();   //[-28, -72, -83, -27, -101, -67]
    2.   byte[] bys = s.getBytes("utf-8");  //[-28, -72, -83, -27, -101, -67]
    3.   //byte[] bys = s.getBytes("GBK");  //[-42, -48, -71, -6]
    4.   System.out.println(Arrays.toString(bys));
  1. ![image.png](https://cdn.nlark.com/yuque/0/2021/png/22084757/1636786828440-782fd577-73b2-421b-a615-fe19c2025d39.png#clientId=ua254ed71-1215-4&crop=0&crop=0&crop=1&crop=1&from=paste&id=uacd226df&margin=%5Bobject%20Object%5D&name=image.png&originHeight=526&originWidth=1073&originalType=binary&ratio=1&rotation=0&showTitle=false&size=238888&status=done&style=none&taskId=uae8bf92c-a1ec-430f-ad19-ebb4a41577e&title=)<br />![image.png](https://cdn.nlark.com/yuque/0/2021/png/22084757/1636786919193-12981e2a-7623-4a8a-88e3-a0aa59bd7fdd.png#clientId=ua254ed71-1215-4&crop=0&crop=0&crop=1&crop=1&from=paste&id=ub462fdf9&margin=%5Bobject%20Object%5D&name=image.png&originHeight=437&originWidth=981&originalType=binary&ratio=1&rotation=0&showTitle=false&size=206743&status=done&style=none&taskId=ubbac426c-0e0c-41bf-a923-9176ba19e16&title=)
  2. <a name="CptDh"></a>
  3. ## 读取文件
  4. ```java
  5. public static void main(String[] args) throws IOException {
  6.         String s = "中国";
  7.         byte[] bys = s.getBytes("GBK");  //[-42, -48, -71, -6]
  8.         System.out.println(Arrays.toString(bys));
  10.         //用何编码,应以其解码,否则会乱码
  11.         String ss = new String(bys);
  12.         System.out.println(ss);  //�й�
  14.         String ss1 = new String(bys,"GBK");
  15.         System.out.println(ss1);  //中国
  16.     }
  1. /**
  2.      * 字符流编码
  3.      * @param args
  4.      */
  5.     public static void main(String[] args) throws IOException {
  6.               //字符流写入
  7.         OutputStreamWriter osw = new OutputStreamWriter(new FileOutputStream("src\\owx.txt"), "utf-8");
  8.         osw.write("中国");  //默认utf-8编码
  9.         osw.write("你好世界", 2, 2);  //只写入"世界"
  10.         osw.flush(); //刷新,从缓冲区存入
  11.         osw.close();
  13.         //字符流读取数据
  14.         InputStreamReader isr = new InputStreamReader(new FileInputStream("src\\Test01.java"), "utf-8");
  15.         //一次读一个字符
  16. //        int i;
  17. //        while ((i=isr.read())!=-1){
  18. //            System.out.print((char)i); //中国世界
  19. //        }
  21.         // 一次读一个数组
  22.         char[] chars = new char[1024];
  23.         int len;
  24.         while ((len = isr.read(chars)) != -1) {
  25.             System.out.println(new String(chars));
  26.         }
  27.         isr.close();
  28.     }

字符流复制—便捷类FileWriter-FileReader

  1. public static void main(String[] args) throws IOException {
  2.         FileReader fd = new FileReader("src\\taobao.txt");
  3.         FileWriter fw = new FileWriter("src\\copy.txt");
  4.         char[] chars = new char[1024];
  5.         int len;
  6.         while ((len=fd.read(chars))!=-1){
  7.             fw.write(chars);
  8.         }
  9.         fd.close();
  10.         fw.close();
  11.     }

字符缓冲流

image.png
使用字节缓冲流复制文件

  1.  public static void main(String[] args) throws IOException {
  2.         BufferedReader br = new BufferedReader(new FileReader("src\\taobao.txt"));
  3.         BufferedWriter bw = new BufferedWriter(new FileWriter("src\\copy.txt"));
  5.         char[] chars = new char[1024];
  6.         int len;
  7.         while ((len=br.read(chars))!=-1){
  8.             bw.write(chars);
  9.         }
  10.         br.close();
  11.         bw.close();
  12.     }

换行与一行读取

  1.  public static void main(String[] args) throws IOException {
  2.         BufferedReader br = new BufferedReader(new FileReader("src\\taobao.txt"));
  3.         BufferedWriter bw = new BufferedWriter(new FileWriter("src\\copy.txt"));
  5.        bw.write("你好");
  6.        bw.newLine(); //换行
  8.         String line;  //一行一行读取
  9.         while ((line = br.readLine())!=null){
  10.             System.out.println(line);
  11.         }
  13.         br.close();
  14.         bw.close();
  15.     }

最常用方式— 复制文件

  1. public static void main(String[] args) throws IOException {
  2.         BufferedReader br = new BufferedReader(new FileReader("src\\taobao.txt"));
  3.         BufferedWriter bw = new BufferedWriter(new FileWriter("src\\copy.txt"));
  5.         String line;  //一行一行读取
  6.         while ((line = br.readLine())!=null){
  7.             bw.write(line);
  8.             bw.newLine();
  9.             bw.flush();
  10.         }
  12.         br.close();
  13.         bw.close();
  14.     }
  15. }

image.png
image.png

点名

  1. public class Demo {
  2.     /**
  3.      * 从文件中随机抽取一行
  4.      * @param args
  5.      * @throws IOException
  6.      */
  7.     public static void main(String[] args) throws IOException {
  8.         ArrayList<String> arr = new ArrayList<>();
  9.         BufferedReader br = new BufferedReader(new FileReader("src\\taobao.txt"));
  10.         String line;  //一行一行读取
  11.         while ((line = br.readLine())!=null){
  12.             arr.add(line);
  13.         }
  14.         br.close();
  15.         Random random = new Random();
  16.         int index = random.nextInt(arr.size());
  17.         String name = arr.get(index);
  18.         System.out.println(name);
  19.     }
  20. }

集合对象写入

  2.     public static void main(String[] args) throws IOException {
  3.         ArrayList<Student> students = new ArrayList<>();
  4.         Student s1 = new Student("鞠婧祎",25,"武汉");
  5.         Student s2 = new Student("马保国",60,"重庆");
  6.         Student s3 = new Student("薛之谦",25,"上海");
  7.         students.add(s1);
  8.         students.add(s2);
  9.         students.add(s3);
  11.         BufferedWriter bw = new BufferedWriter(new FileWriter("src\\copy.txt"));
  12.         for (Student s:students){
  13.             bw.write(s.getName()+"--"+s.getAge()+"--"+s.getAddress());
  14.             bw.newLine();
  15.         }
  16.         bw.close();
  17.     }

复制单级文件夹—-有问题

  1. public static void main(String[] args) throws IOException {
  2.         File file = new File("src\\duoc");
  3.         String srcname = file.getName();
  4.         File dest = new File("TestStudy",srcname);
  6.         if (!dest.exists()){
  7.             dest.mkdir();
  8.         }
  10.         File[] listFile = file.listFiles();
  12.         for (File f:listFile){
  13.             String srcFileName = f.getName();
  14.             File destFile = new File(dest,srcFileName);
  15.             copyFile(f,destFile);
  16.         }
  17.     }
  19.     public static void copyFile(File srcFile,File destFile) throws IOException {
  20.         BufferedInputStream bis = new BufferedInputStream(new FileInputStream(srcFile));
  21.         BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(destFile));
  23.         byte[] bys = new byte[1024];
  24.         int len;
  25.         while ((len=bis.read(bys))!=-1){
  26.             bos.write(bys,0,len);
  27.         }
  28.         bos.close();
  29.         bis.close();
  32.     }

复制多级文件夹—递归

….

打印流复制文件

只能写不能读
printWriter

对象序列化流

ObjectOutputStream

对象反序列化流

ObjectItputStream

关键字 修饰符transient

使用transient修饰 成员变量将不参与序列化

Properties集合类

猜数字游戏,限制游戏次数

  1. public class Demo {
  2.     /**
  3.      * 从文件中随机抽取一行
  4.      * @param args
  5.      * @throws IOException
  6.      */
  7.     public static void main(String[] args) throws IOException {
  8.         Properties prop = new Properties();
  9.         FileReader fr = new FileReader("src\\owx.txt");
  10.         //文件写入 count = 0
  11.         prop.load(fr);
  12.         fr.close();
  14.         String count = prop.getProperty("count");
  15.         int number = Integer.parseInt(count);
  17.         if (number>2){
  18.             System.out.println("请充值后继续");
  19.         }else{
  20.             Demo.GuessNumber();
  21.             number++;
  22.             prop.setProperty("count",String.valueOf(number));
  23.             FileWriter fw = new FileWriter("src\\owx.txt");
  24.             prop.store(fw,null);
  25.             fw.close();
  26.         }
  27.     }
  29.     public static void GuessNumber(){
  30.         Random r = new Random();
  31.         int number = r.nextInt(100)+1;
  33.         while (true){
  34.             Scanner sc = new Scanner(System.in);
  35.             System.out.print("请输入猜的数值:");
  36.             int guessNum = sc.nextInt();
  37.             if (guessNum>number){
  38.                 System.out.println("大了哦");
  39.             }else if (guessNum<number){
  40.                 System.out.println("小了点");
  41.             }else{
  42.                 System.out.println("猜对了");
  43.                 break;
  44.             }
  45.         }
  46.     }
  47. }

进程与线程

image.png

多线程的实现方式

方式一:继承Thread类

  1. 继承Tread类
  2. 重写run()方法
  3. 创建类对象

  4. 启动线程

    1. class Demo{
    2.  public static void main(String[] args) {
    3.      MyThread m1 = new MyThread();
    4.      MyThread m2 = new MyThread();
    5.      //普通方式
    6. //        m1.run();
    7. //        m2.run();
    9.      //以start启动线程,再由JVM调用run方法
    10.      //不会等到m1的run方法跑完就会执行m2的run方法
    11.      m1.start();
    12.      m2.start();
    13.  }
    14. }
    1. public class MyThread extends Thread {
    2.  @Override
    3.  public void run() {
    4.      int i = 0;
    5.      while (i<100){
    6.          System.out.println(i++);
    7.      }
    8.  }
    9. }

    设定与获取线程名称

    不设置获取默认值
    线程名称默认值
    第一次调用: Thread-0
    第二次调用: Thread-1

    1.  public static void main(String[] args) {
    2.      MyThread m1 = new MyThread();
    3.      MyThread m2 = new MyThread();
    4.      //普通方式
    5. //        m1.run();
    6. //        m2.run();
    8.      //以start启动线程,再由JVM调用run方法
    9.      //不会等到m1的run方法跑完就会执行m2的run方法
    10.      m1.setName("飞机");
    11.      System.out.println(m1.getName());
    12.      m1.start();
    13.      m2.setName("大炮");
    14.      System.out.println(m2.getName());
    15.      m2.start();
    16.  }

    或者提供一个带参构造方法

    1. public static void main(String[] args) {
    2.      MyThread m1 = new MyThread("飞机");
    3.      MyThread m2 = new MyThread("大炮");
    4.      //普通方式
    5. //        m1.run();
    6. //        m2.run();
    8.      //以start启动线程,再由JVM调用run方法
    9.      //不会等到m1的run方法跑完就会执行m2的run方法
    10.      System.out.println(m1.getName());
    11.      m1.start();
    12.      System.out.println(m2.getName());
    13.      m2.start();
    14.  }
    1. class Demo{
    2.  public static void main(String[] args) {
    3.      //返回当前正在执行的线程名称
    4.      System.out.println(Thread.currentThread().getName());
    5.      //main
    6.  }
    7. }

    线程调度模型

  • 分时调度模型
  • 抢占式调度模型

image.png

java使用的是抢占式调度模型
随机性
优先级—存在范围 [1,10]
默认值— 5

  1.         m1.setPriority(10);
  2.         m3.setPriority(1);

线程控制

image.png

  1.  @Override
  2.     public void run() {
  3.         int i = 0;
  4.         while (i<100){
  5.             System.out.println(getName()+"--"+i++);
  6.             try {
  7.                 Thread.sleep(1000);  //每隔1秒执行每个线程一次
  8.             } catch (InterruptedException e) {
  9.                 e.printStackTrace();
  10.             }
  11.         }
  12.     }
  1. public static void main(String[] args) {
  2.         MyThread m1 = new MyThread("飞机");
  3.         MyThread m2 = new MyThread("高铁");
  4.         MyThread m3 = new MyThread("骑车");
  5. //        m1.setPriority(10);
  6. //        m3.setPriority(1);
  8.         m1.start();
  9.         try {
  10.             m1.join();  //只有m1线程停止后,才执行其他线程
  11.         } catch (InterruptedException e) {
  12.             e.printStackTrace();
  13.         }
  14.         m2.start();
  15.         m3.start();
  16.     }

守护线程 —不是立即结束!!

  1. class Demo{
  2.     public static void main(String[] args) {
  3.         MyThread m1 = new MyThread("飞机");
  4.         MyThread m2 = new MyThread("高铁");
  5.         MyThread m3 = new MyThread("骑车");
  6. //        m1.setPriority(10);
  7. //        m3.setPriority(1);
  9.         m1.start();
  10.         m2.start();
  11.         m2.setDaemon(true); //设定为守护线程,主线程结束后,守护线程应也马上结束
  12.         m3.start();
  13.         m3.setDaemon(true);
  15.         Thread.currentThread().setName("主线程");
  16.         int i = 0;
  17.         while (i<10){
  18.             System.out.println(Thread.currentThread().getName()+"--"+i++);
  19.         }
  20.     }
  21. }

线程的生命周期

image.png

方式二:实现Runnable接口

  1. public class MyThread implements Runnable {
  2.     public MyThread() {
  3.     }
  5.     @Override
  6.     public void run() {
  7.         int i = 0;
  8.         while (i<100){
  9.             System.out.println(Thread.currentThread().getName()+"--"+i++);
  10. //            try {
  11. //                Thread.sleep(1000);  //每隔1秒执行每个线程一次
  12. //            } catch (InterruptedException e) {
  13. //                e.printStackTrace();
  14. //            }
  15.         }
  16.     }
  17. }
  1. class Demo{
  2.     public static void main(String[] args) {
  3.         MyThread m = new MyThread();
  5.         Thread t1 = new Thread(m,"飞机");
  6.         Thread t2 = new Thread(m,"火车");
  8.         t1.start();
  9.         t2.start();
  10.     }
  11. }

image.png

卖票案例

image.png

  1. public class MyThread implements Runnable {
  2.     private int tickets = 100; //总票数
  3.     private Object obj = new Object();
  5.     public MyThread() {
  6.     }
  10.     @Override
  11.     public void run() {
  12.        while (true){
  13.            //解决线程同步安全问题,将不会出现两个窗口同时出售同一张票的情况
  14.            synchronized (obj){
  15.                try {
  16.                    Thread.sleep(100);
  17.                } catch (InterruptedException e) {
  18.                    e.printStackTrace();
  19.                }
  20.                if(tickets > 0){
  21.                    System.out.println(Thread.currentThread().getName()+"正在出售第"+tickets--+"张票");
  22.                }
  23.            }
  24.        }
  25.     }
  26. }
  1. public static void main(String[] args) {
  2.         MyThread m = new MyThread();
  4.         Thread t1 = new Thread(m,"VIP窗口");
  5.         Thread t2 = new Thread(m,"普通窗口");
  6.         Thread t3 = new Thread(m,"附加窗口");
  8.         t1.setPriority(8);
  9.         t3.setPriority(2);
  11.         t1.start();
  12.         t2.start();
  13.         t3.start();
  14.     }

同步方法锁定this

以修饰符 synchronized 修饰方法
image.png