如何编写和读取dat文件

Question

Write a program that asks the user to enter whole numbers (they enter –1 to finish data entry). The numbers are to be written to a binary file. This is to be done in a method called writeBinaryFile() . Then the program should read the numbers from the binary file and display them to the console. This should be done in a method called readBinaryFile() . The main() method should just call writeBinaryFile() then readBinaryFile() .

My code so far:

public static void main(String[] args) throws FileNotFoundException, IOException {
    System.out.println("Please enter whole numbers then enter -1 to data entry.");
    writeBinaryFile();
    readBinaryFile();
}

/**
 * This method opens a binary file and writes the contents
 * of an int array to the file.
 */
private static void writeBinaryFile() throws IOException, FileNotFoundException
{
    Scanner input = new Scanner(System.in);
    ArrayList<Integer> number = new ArrayList<Integer>();
    try
    {
        FileOutputStream output = new FileOutputStream("Files//Numbers.dat");
        int numbers = 0;

        while(numbers != -1)
        {
            number.add(numbers = input.nextInt());

            output.write(numbers);
        }
        output.close();
    }
    catch(IOException ex)
    {
        ex.getMessage();
    }
}

private static void readBinaryFile() throws IOException
{
    FileInputStream input = new FileInputStream("Files//Numbers.dat");
    int value;
    value = input.read();
    System.out.print("The numbers in the file are:  ");
    try
    {
        while(value != -1)
        {
            System.out.print(value +" ");
            value = input.read();
        }
        input.close();
    }
    catch(IOException ex)
    {
        ex.getMessage();
    }
}

The problem is that when I enter this data:

5 2 4 6 8 4 -1

My output is:

5 2 4 6 8 4 255

How can I stop 255 from coming up?

Answer 1

You should avoid adding -1 to input. The problem is at line: number.add(numbers = input.nextInt()); in loop.

EDIT: To write binary data you should use DataInputStream/DataOutputStream . You cannot mix it with Scanner as that is primarily for text data. A sample example is:

public static void main(String[] args) throws IOException {
    writeNumbers();
    readNumbers();
}

private static void writeNumbers() throws IOException {
        DataOutputStream output = new DataOutputStream(new FileOutputStream("C://Numbers.dat"));
        for (int i = 0; i < 10; i++) {
            output.writeInt(i);
            System.out.println(i);
        }
        output.close();
    }

private static void readNumbers() throws IOException{
        DataInputStream input = new DataInputStream(new FileInputStream("C://Numbers.dat"));
        while (input.available() > 0) {
            int x = input.readInt();
            System.out.println(x);
        }
        input.close();
    }

Answer 2

try doing like this...

 while(numbers = input.nextInt())!=-1)
        {
            number.add(numbers);

            output.write(numbers);
        }

Answer 3

Just update @akhul_mittal answer to include reading from standard input using Scanner.

public static void main(String[] args) throws IOException {
    writeNumbers();
    readNumbers();
}

private static void writeNumbers() throws IOException {
    DataOutputStream output = new DataOutputStream(new FileOutputStream("C://Numbers.dat"));
    Scanner scanner = new Scanner(System.in);
    int n = scanner.nextInt();
    while (n != -1) {
        output.writeInt(n);
        n = scanner.nextInt();
    }
    output.close();
}

private static void readNumbers() throws IOException {
    DataInputStream input = new DataInputStream(new FileInputStream("C://Numbers.dat"));
    while (input.available() > 0) {
        int x = input.readInt();
        System.out.println(x);
    }
    input.close();
}