1.IO flow cases

1.1 improved version of collection to file data sorting [application]

1.1. 1 case requirements

• Enter 5 student information (name, Chinese score, mathematics score and English score) on the keyboard. It is required to write the text file from high to low according to the total score
• Format: name, Chinese score, math score, English score example: Lin Qingxia, 98,99100

1.1. 2 analysis steps

1. Define student classes
2. Create a TreeSet collection and sort by comparator sorting
3. Enter student data with keyboard
4. Create a student object and assign the data entered on the keyboard to the member variable of the student object
5. Add the student object to the TreeSet collection
6. Create character buffered output stream object
7. Traverse the collection to get each student object
8. Splice the data of the student object into a string in the specified format
9. Call the method of character buffered output stream object to write data
10. Release resources

1.1. 3 code implementation

• Student class

public class Student {
    // full name
    private String name;
    // grade scores of Chinese
    private int chinese;
    // Mathematics achievement
    private int math;
    // English achievement
    private int english;
    public Student() {
        super();
    }
    public Student(String name, int chinese, int math, int english) {
        super();
        this.name = name;
        this.chinese = chinese;
        this.math = math;
        this.english = english;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getChinese() {
        return chinese;
    }
    public void setChinese(int chinese) {
        this.chinese = chinese;
    }
    public int getMath() {
        return math;
    }
    public void setMath(int math) {
        this.math = math;
    }
    public int getEnglish() {
        return english;
    }
    public void setEnglish(int english) {
        this.english = english;
    }
    public int getSum() {
        return this.chinese + this.math + this.english;
    }
}

• Test class

public class TreeSetToFileDemo {
    public static void main(String[] args) throws IOException {
        //Create a TreeSet collection and sort by comparator sorting
        TreeSet<Student> ts = new TreeSet<Student>(new Comparator<Student>() {
            @Override
            public int compare(Student s1, Student s2) {
                //Total score from high to low
                int num = s2.getSum() - s1.getSum();
                //minor criteria 
                int num2 = num == 0 ? s1.getChinese() - s2.getChinese() : num;
                int num3 = num2 == 0 ? s1.getMath() - s2.getMath() : num2;
                int num4 = num3 == 0 ? s1.getName().compareTo(s2.getName()) : num3;
                return num4;
            }
        });

        //Enter student data with keyboard
        for (int i = 0; i < 5; i++) {
            Scanner sc = new Scanner(System.in);
            System.out.println("Please enter page" + (i + 1) + "Student information:");
            System.out.println("full name:");
            String name = sc.nextLine();
            System.out.println("Language achievement:");
            int chinese = sc.nextInt();
            System.out.println("Math scores:");
            int math = sc.nextInt();
            System.out.println("English score:");
            int english = sc.nextInt();

            //Create a student object and assign the data entered on the keyboard to the member variable of the student object
            Student s = new Student();
            s.setName(name);
            s.setChinese(chinese);
            s.setMath(math);
            s.setEnglish(english);

            //Add the student object to the TreeSet collection
            ts.add(s);
        }

        //Create character buffered output stream object
        BufferedWriter bw = new BufferedWriter(new FileWriter("myCharStream\\ts.txt"));

        //Traverse the collection to get each student object
        for (Student s : ts) {
            //Splice the data of the student object into a string in the specified format
            //Format: name, Chinese score, math score, English score
            StringBuilder sb = new StringBuilder();
            sb.append(s.getName()).append(",").append(s.getChinese()).append(",").append(s.getMath()).append(",").append(s.getEnglish()).append(",").append(s.getSum());

		//Call the method of character buffered output stream object to write data
            bw.write(sb.toString());
            bw.newLine();
            bw.flush();
        }
        //Release resources
        bw.close();
    }
}

1.2 copy single level folder [ application ]

1.2. 1 case requirements

• Copy the folder "E:\itcast" to the module directory

1.2. 2 analysis steps

1. Create a data source directory File object with the path E:\itcast
2. Gets the name of the File object in the data source directory
3. Create a destination directory File object. The path consists of (module name + name obtained in step 2)
4. Judge whether the File created in step 3 exists. If it does not exist, create it
5. Get the File array of all files in the data source directory
6. Traverse the File array to get each File object, which is actually the data source File
7. Gets the name of the File object of the data source File
8. Create a destination File object. The path consists of (destination directory + the name obtained in step 7)
9. Copy file
   Because it is not clear what type of files are in the data source directory, byte stream is used to copy files
   The construction method with the parameter File is adopted

1.2. 3 code implementation

public class CopyFolderDemo {
    public static void main(String[] args) throws IOException {
        //Create a data source directory File object with the path E:\itcast
        File srcFolder = new File("E:\\itcast");

        //Get the name of the File object in the data source directory (itcast)
        String srcFolderName = srcFolder.getName();

        //Create a destination directory File object. The path name is composed of module name + itcast (myCharStream\itcast)
        File destFolder = new File("myCharStream",srcFolderName);

        //Judge whether the File corresponding to the destination directory exists. If it does not exist, create it
        if(!destFolder.exists()) {
            destFolder.mkdir();
        }

        //Get the File array of all files in the data source directory
        File[] listFiles = srcFolder.listFiles();

        //Traverse the File array to get each File object, which is actually the data source File
        for(File srcFile : listFiles) {
            //Data source file: e: \ \ itcast \ \ Mn jpg
            //Get the name of the File object of the data source File (mn.jpg)
            String srcFileName = srcFile.getName();
            //Create a destination File object with the pathname of destination directory + Mn Jpg composition (myCharStream\itcast\mn.jpg)
            File destFile = new File(destFolder,srcFileName);
            //Copy file
            copyFile(srcFile,destFile);
        }
    }

    private static void copyFile(File srcFile, File destFile) throws IOException {
        BufferedInputStream bis = new BufferedInputStream(new FileInputStream(srcFile));
        BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(destFile));

        byte[] bys = new byte[1024];
        int len;
        while ((len=bis.read(bys))!=-1) {
            bos.write(bys,0,len);
        }

        bos.close();
        bis.close();
    }
}

1.3 copy multi-level folders [ application ]

1.3. 1 case requirements

• Copy the folder "E:\itcast" to the directory of disk F

1.3. 2 analysis steps

1. Create a data source File object with the path E:\itcast
2. Create a destination File object with the path F:\
3. The write method copies the folder. The parameters are the data source File object and the destination File object
4. Determine whether the data source File is a File
   Yes file: copy directly, using byte stream
   Not a file:
   Create the directory at the destination
   Traverse the File array of all files in the directory to get each File object
   Go back to 3 and continue (recursion)

1.3. 3 code implementation

public class CopyFoldersDemo {
    public static void main(String[] args) throws IOException {
        //Create a data source File object with the path E:\itcast
        File srcFile = new File("E:\\itcast");
        //Create a destination File object with the path F:\
        File destFile = new File("F:\\");

        //The write method copies the folder. The parameters are the data source File object and the destination File object
        copyFolder(srcFile,destFile);
    }

    //Copy folder
    private static void copyFolder(File srcFile, File destFile) throws IOException {
        //Determine whether the data source File is a directory
        if(srcFile.isDirectory()) {
            //Create a directory under the destination with the same name as the data source File
            String srcFileName = srcFile.getName();
            File newFolder = new File(destFile,srcFileName); //F:\\itcast
            if(!newFolder.exists()) {
                newFolder.mkdir();
            }

            //Get the File array of all files or directories under the data source File
            File[] fileArray = srcFile.listFiles();

            //Traverse the File array to get each File object
            for(File file : fileArray) {
                //Take the File as the data source File object and recursively call the method of copying the folder
                copyFolder(file,newFolder);
            }
        } else {
            //Description is a file, directly copied, with byte stream
            File newFile = new File(destFile,srcFile.getName());
            copyFile(srcFile,newFile);
        }
    }

    //Byte buffer stream copy file
    private static void copyFile(File srcFile, File destFile) throws IOException {
        BufferedInputStream bis = new BufferedInputStream(new FileInputStream(srcFile));
        BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(destFile));

        byte[] bys = new byte[1024];
        int len;
        while ((len = bis.read(bys)) != -1) {
            bos.write(bys, 0, len);
        }

        bos.close();
        bis.close();
    }
}

1.4 exception handling of copied documents [ application ]

1.4. 1. Basic practice

public class CopyFileDemo {
    public static void main(String[] args) {
    }
    //try...catch...finally
    private static void method2() {
        FileReader fr = null;
        FileWriter fw = null;
        try {
            fr = new FileReader("fr.txt");
            fw = new FileWriter("fw.txt");

            char[] chs = new char[1024];
            int len;
            while ((len = fr.read()) != -1) {
                fw.write(chs, 0, len);
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if(fw!=null) {
                try {
                    fw.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if(fr!=null) {
                try {
                    fr.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    //Throw processing
    private static void method1() throws IOException {
        FileReader fr = new FileReader("fr.txt");
        FileWriter fw = new FileWriter("fw.txt");

        char[] chs = new char[1024];
        int len;
        while ((len = fr.read()) != -1) {
            fw.write(chs, 0, len);
        }

        fw.close();
        fr.close();
    }
}

1.4.2JDK7 version improvement

public class CopyFileDemo {
    public static void main(String[] args) {
    }
    //Improvement scheme of JDK7
    private static void method3() {
        try(FileReader fr = new FileReader("fr.txt");
            FileWriter fw = new FileWriter("fw.txt");){
            char[] chs = new char[1024];
            int len;
            while ((len = fr.read()) != -1) {
                fw.write(chs, 0, len);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

1.4.3JDK9 version improvement

public class CopyFileDemo {
    public static void main(String[] args) {
    }
    //Improvement scheme of JDK9
    private static void method4() throws IOException {
        FileReader fr = new FileReader("fr.txt");
        FileWriter fw = new FileWriter("fw.txt");
        try(fr;fw){
            char[] chs = new char[1024];
            int len;
            while ((len = fr.read()) != -1) {
                fw.write(chs, 0, len);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

2.IO special operation flow

2.1 standard input stream [application]

• There are two static member variables in the System class

  • public static final InputStream in: standard input stream. Typically, the stream corresponds to keyboard input or another input source specified by the host environment or the user
  • public static final PrintStream out: standard output stream. Typically, the flow corresponds to a display output or another output destination specified by the host environment or the user

• Own keyboard input data

public class SystemInDemo {
    public static void main(String[] args) throws IOException {
        //public static final InputStream in: standard input stream
//        InputStream is = System.in;

//        int by;
//        while ((by=is.read())!=-1) {
//            System.out.print((char)by);
//        }

        //How to convert byte stream to character stream? Convert stream with
//        InputStreamReader isr = new InputStreamReader(is);
//        //Can you read one line of data at a time using character stream? sure
//        //However, the method of reading one line of data at a time is a unique method of character buffered input stream
//        BufferedReader br = new BufferedReader(isr);

        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        System.out.println("Please enter a string:");
        String line = br.readLine();
        System.out.println("The string you entered is:" + line);

        System.out.println("Please enter an integer:");
        int i = Integer.parseInt(br.readLine());
        System.out.println("The integer you entered is:" + i);

        //It's too troublesome to enter data by keyboard, so Java provides a class for us to use
        Scanner sc = new Scanner(System.in);
    }
}

2.2 standard output stream [application]

• There are two static member variables in the System class

  • public static final InputStream in: standard input stream. Typically, the stream corresponds to keyboard input or another input source specified by the host environment or the user
  • public static final PrintStream out: standard output stream. Typically, the flow corresponds to a display output or another output destination specified by the host environment or the user

• The essence of output statement: it is a standard output stream

  • PrintStream ps = System.out;
  • Some methods of PrintStream class, system Out can be used

• Sample code

public class SystemOutDemo {
    public static void main(String[] args) {
        //public static final PrintStream out: standard output stream
        PrintStream ps = System.out;

        //It can easily print various data values
		//ps.print("hello");
		//ps.print(100);

		//ps.println("hello");
		//ps.println(100);

        //System.out is essentially a byte output stream
        System.out.println("hello");
        System.out.println(100);

        System.out.println();
		//System.out.print();
    }
}

2.3 byte print stream [ application ]

• Print stream classification

  • Byte print stream: PrintStream
  • Character print stream: PrintWriter

• Characteristics of print stream

  • It is only responsible for outputting data, not reading data
  • IOException will never be thrown
  • Has its own unique method

• Byte print stream

  • PrintStream(String fileName): creates a new print stream with the specified file name
  • Use the method of inheriting the parent class to write data, and transcode it when viewing; Use your own unique method to write data and view the output of the data as it is
  • You can change the destination of the output statement
    public static void setOut(PrintStream out): reassign the standard output stream

• Sample code

public class PrintStreamDemo {
    public static void main(String[] args) throws IOException {
        //PrintStream(String fileName): creates a new print stream with the specified file name
        PrintStream ps = new PrintStream("myOtherStream\\ps.txt");

        //Write data
        //Some methods of byte output stream
		//ps.write(97);

        //Write data using unique methods
		//ps.print(97);
		//ps.println();
		//ps.print(98);
        ps.println(97);
        ps.println(98);
        
        //Release resources
        ps.close();
    }
}

2.4 character print stream [ application ]

• Construction method of character print stream

  Method name	explain
  PrintWriter(String fileName)	Creates a new PrintWriter with the specified file name without automatic refresh
  PrintWriter(Writer out, boolean autoFlush)	Create a new PrintWriter out: character output stream autoFlush: a Boolean value. If true, the println, printf, or format methods will flush the output buffer

• Sample code

public class PrintWriterDemo {
    public static void main(String[] args) throws IOException {
        //PrintWriter(String fileName): creates a new PrintWriter with the specified file name without automatic line refresh
//        PrintWriter pw = new PrintWriter("myOtherStream\\pw.txt");

//        pw.write("hello");
//        pw.write("\r\n");
//        pw.flush();
//        pw.write("world");
//        pw.write("\r\n");
//        pw.flush();

//        pw.println("hello");
        /*
            pw.write("hello");
            pw.write("\r\n");
         */
//        pw.flush();
//        pw.println("world");
//        pw.flush();

        //PrintWriter(Writer out, boolean autoFlush): create a new PrintWriter
        PrintWriter pw = new PrintWriter(new FileWriter("myOtherStream\\pw.txt"),true);
//        PrintWriter pw = new PrintWriter(new FileWriter("myOtherStream\\pw.txt"),false);

        pw.println("hello");
        /*
            pw.write("hello");
            pw.write("\r\n");
            pw.flush();
         */
        pw.println("world");

        pw.close();
    }
}

2.5 copy Java file print stream improved version [application]

• Case requirements

  • Put printstreamdemo in the module directory Java to Copy.java in the module directory java

• Analysis steps

  • Create character input stream objects from data sources
  • Create a character output stream object based on the destination
  • Read and write data, copy files
  • Release resources

• code implementation

public class CopyJavaDemo {
    public static void main(String[] args) throws IOException {
        /*
        //Create character input stream objects from data sources
        BufferedReader br = new BufferedReader(new FileReader("myOtherStream\\PrintStreamDemo.java"));
        //Create a character output stream object based on the destination
        BufferedWriter bw = new BufferedWriter(new FileWriter("myOtherStream\\Copy.java"));

        //Read and write data, copy files
        String line;
        while ((line=br.readLine())!=null) {
            bw.write(line);
            bw.newLine();
            bw.flush();
        }

        //Release resources
        bw.close();
        br.close();
        */
        //Create character input stream objects from data sources
        BufferedReader br = new BufferedReader(new FileReader("myOtherStream\\PrintStreamDemo.java"));
        //Create a character output stream object based on the destination
        PrintWriter pw = new PrintWriter(new FileWriter("myOtherStream\\Copy.java"),true);

        //Read and write data, copy files
        String line;
        while ((line=br.readLine())!=null) {
            pw.println(line);
        }
        //Release resources
        pw.close();
        br.close();
    }
}

2.6 object serialization stream [application]

• Introduction to object serialization

  • Object serialization: saving objects to disk or transferring objects over the network
  • This mechanism uses a byte sequence to represent an object, which contains information such as object type, object data and attributes stored in the object
  • After the byte sequence is written to the file, it is equivalent to persisting the information of an object in the file
  • On the contrary, the byte sequence can also be read back from the file, reconstruct the object and deserialize it

• Object serialization stream: ObjectOutputStream

  • Writes the original data type and graph of the Java object to the OutputStream. You can use ObjectInputStream to read (refactor) objects. Persistent storage of objects can be achieved by using streaming files. If the stream is a network socket stream, you can refactor the object on another host or in another process

• Construction method

  Method name	explain
  ObjectOutputStream(OutputStream out)	Creates an ObjectOutputStream that writes to the specified OutputStream

• Methods for serializing objects

  Method name	explain
  void writeObject(Object obj)	Writes the specified object to ObjectOutputStream

• Sample code

  • Student class

    public class Student implements Serializable {
        private String name;
        private int age;
        public Student() {
        }
        public Student(String name, int age) {
            this.name = name;
            this.age = age;
        }
        public String getName() {
            return name;
        }
        public void setName(String name) {
            this.name = name;
        }
        public int getAge() {
            return age;
        }
        public void setAge(int age) {
            this.age = age;
        }
        @Override
        public String toString() {
            return "Student{" +
                    "name='" + name + '\'' +
                    ", age=" + age +
                    '}';
        }
    }
    

  • Test class

    public class ObjectOutputStreamDemo {
        public static void main(String[] args) throws IOException {
            //ObjectOutputStream(OutputStream out): creates an ObjectOutputStream that writes to the specified OutputStream
            ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("myOtherStream\\oos.txt"));
    
            //create object
            Student s = new Student("Lin Qingxia",30);
    
            //void writeObject(Object obj): writes the specified object to ObjectOutputStream
            oos.writeObject(s);
    
            //Release resources
            oos.close();
        }
    }
    

• matters needing attention

  • To serialize an object, the class to which the object belongs must implement the Serializable interface
  • Serializable is a tag interface that can be implemented without rewriting any methods

2.7 object deserialization stream [application]

• Object deserialization stream: ObjectInputStream

  • ObjectInputStream deserializes raw data and objects previously written using ObjectOutputStream

• Construction method

  Method name	explain
  ObjectInputStream(InputStream in)	Creates an ObjectInputStream read from the specified InputStream

• Method of deserializing object

  Method name	explain
  Object readObject()	Read an object from ObjectInputStream

• Sample code

public class ObjectInputStreamDemo {
    public static void main(String[] args) throws IOException, ClassNotFoundException {
        //ObjectInputStream(InputStream in): creates an ObjectInputStream read from the specified InputStream
        ObjectInputStream ois = new ObjectInputStream(new FileInputStream("myOtherStream\\oos.txt"));

        //Object readObject(): reads an object from ObjectInputStream
        Object obj = ois.readObject();

        Student s = (Student) obj;
        System.out.println(s.getName() + "," + s.getAge());
        
        ois.close();
    }
}

2.8 serialVersionUID & transient [application]

• serialVersionUID

  • After serializing an object with the object serialization stream, if we modify the class file to which the object belongs, will there be a problem reading the data?
    • There will be a problem and an InvalidClassException will be thrown
  • If something goes wrong, how to solve it?
    • Re serialization
    • Add a serialVersionUID to the class to which the object belongs
      • private static final long serialVersionUID = 42L;

• transient

  • If the value of a member variable in an object does not want to be serialized, how to implement it?
    • The member variable is decorated with the transient keyword. The member variable marked with the keyword does not participate in the serialization process

• Sample code

  • Student class

    public class Student implements Serializable {
        private static final long serialVersionUID = 42L;
        private String name;
    	//private int age;
        private transient int age;
        public Student() {
        }
        public Student(String name, int age) {
            this.name = name;
            this.age = age;
        }
        public String getName() {
            return name;
        }
        public void setName(String name) {
            this.name = name;
        }
        public int getAge() {
            return age;
        }
        public void setAge(int age) {
            this.age = age;
        }
    //    @Override
    //    public String toString() {
    //        return "Student{" +
    //                "name='" + name + '\'' +
    //                ", age=" + age +
    //                '}';
    //    }
    }
    

  • Test class

    public class ObjectStreamDemo {
        public static void main(String[] args) throws IOException, ClassNotFoundException {
    //        write();
            read();
        }
        //Deserialization
        private static void read() throws IOException, ClassNotFoundException {
            ObjectInputStream ois = new ObjectInputStream(new FileInputStream("myOtherStream\\oos.txt"));
            Object obj = ois.readObject();
            Student s = (Student) obj;
            System.out.println(s.getName() + "," + s.getAge());
            ois.close();
        }
        //serialize
        private static void write() throws IOException {
            ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("myOtherStream\\oos.txt"));
            Student s = new Student("Lin Qingxia", 30);
            oos.writeObject(s);
            oos.close();
        }
    }
    

3.Properties collection

3.1 use of properties as Map set [application]

• Properties introduction

  • Is a collection class of Map system
  • Properties can be saved to or loaded from a stream
  • Each key in the attribute list and its corresponding value is a string

• Properties basic usage

public class PropertiesDemo01 {
    public static void main(String[] args) {
        //Create collection object
//        Properties<String,String> prop = new Properties<String,String>(); // error
        Properties prop = new Properties();

        //Storage element
        prop.put("itheima001", "Lin Qingxia");
        prop.put("itheima002", "Zhang Manyu");
        prop.put("itheima003", "Wang Zuxian");

        //Traversal set
        Set<Object> keySet = prop.keySet();
        for (Object key : keySet) {
            Object value = prop.get(key);
            System.out.println(key + "," + value);
        }
    }
}

3.2 properties as a unique method of Map set [application]

• Unique method

  Method name	explain
  Object setProperty(String key, String value)	Set the keys and values of the collection, which are of String type. The bottom layer calls the Hashtable put method
  String getProperty(String key)	Search for attributes using the key specified in this attribute list
  Set stringPropertyNames()	Returns a non modifiable key set from the property list, where the key and its corresponding value are strings

• Sample code

public class PropertiesDemo02 {
    public static void main(String[] args) {
        //Create collection object
        Properties prop = new Properties();

        //Object setProperty(String key, String value): sets the key and value of the collection, both of which are of String type. The bottom layer calls the Hashtable put method
        prop.setProperty("itheima001", "Lin Qingxia");
        /*
            Object setProperty(String key, String value) {
                return put(key, value);
            }

            Object put(Object key, Object value) {
                return map.put(key, value);
            }
         */
        prop.setProperty("itheima002", "Zhang Manyu");
        prop.setProperty("itheima003", "Wang Zuxian");

        //String getProperty(String key): use the key specified in this property list to search for properties
		//System.out.println(prop.getProperty("itheima001"));
		//System.out.println(prop.getProperty("itheima0011"));

		//System.out.println(prop);

        //Set < string > stringpropertynames(): returns a non modifiable key set from the property list, where the key and its corresponding value are strings
        Set<String> names = prop.stringPropertyNames();
        for (String key : names) {
			//System.out.println(key);
            String value = prop.getProperty(key);
            System.out.println(key + "," + value);
        }
    }
}

3.3Properties and IO flow [application]

• Method combined with IO stream

  Method name	explain
  void load(InputStream inStream)	Read the attribute list (key and element pairs) from the input byte stream
  void load(Reader reader)	Read the attribute list (key and element pairs) from the input character stream
  void store(OutputStream out, String comments)	Write this list of Properties (key and element pairs) to this Properties table and write the output byte stream in a format suitable for using the load(InputStream) method
  void store(Writer writer, String comments)	Write this list of Properties (key and element pairs) to this Properties table and write the output character stream in a format suitable for using the load(Reader) method

• Sample code

public class PropertiesDemo03 {
    public static void main(String[] args) throws IOException {
        //Save the data in the collection to a file
		//myStore();
        //Load the data in the file into the collection
        myLoad();

    }

    private static void myLoad() throws IOException {
        Properties prop = new Properties();
        //void load(Reader reader): 
        FileReader fr = new FileReader("myOtherStream\\fw.txt");
        prop.load(fr);
        fr.close();

        System.out.println(prop);
    }

    private static void myStore() throws IOException {
        Properties prop = new Properties();
        prop.setProperty("itheima001","Lin Qingxia");
        prop.setProperty("itheima002","Zhang Manyu");
        prop.setProperty("itheima003","Wang Zuxian");

        //void store(Writer writer, String comments): 
        FileWriter fw = new FileWriter("myOtherStream\\fw.txt");
        prop.store(fw,null);
        fw.close();
    }
}

3.4 number of games [application]

• Case requirements

  • The number guessing game can only be played for 3 times. If you still want to play, you will be prompted that the game trial is over. If you want to play, please recharge (www.itcast.cn)

• Analysis steps

  1. Write a game class, which has a small game of guessing numbers

  2. Write a test class. The test class has the main() method, and the following code is written in the main() method:
     Read the data from the file to the Properties collection and implement it with the load() method
     File already exists: game txt
     There is a data value: count=0

     Get the number of games played through the Properties collection
     Judge whether the number of times has reached 3
     If you arrive, give a prompt: the game trial is over. If you want to play, please recharge (www.itcast.cn)
     If less than 3 times:
     Times + 1, write back the file, and use the store() method of Properties to play the game

• code implementation

public class PropertiesTest {
    public static void main(String[] args) throws IOException {
        //Read the data from the file to the Properties collection and implement it with the load() method
        Properties prop = new Properties();

        FileReader fr = new FileReader("myOtherStream\\game.txt");
        prop.load(fr);
        fr.close();

        //Get the number of games played through the Properties collection
        String count = prop.getProperty("count");
        int number = Integer.parseInt(count);

        //Judge whether the number of times has reached 3
        if(number >= 3) {
            //If you arrive, give a prompt: the game trial is over. If you want to play, please recharge (www.itcast.cn)
            System.out.println("The game trial has ended. Please recharge if you want to play(www.itcast.cn)");
        } else {
            //play a game
            GuessNumber.start();

            //Times + 1, write back the file and use the store() method of Properties
            number++;
            prop.setProperty("count",String.valueOf(number));
            FileWriter fw = new FileWriter("myOtherStream\\game.txt");
            prop.store(fw,null);
            fw.close();
        }
    }
}