java - 将偶数和奇数写入 da 文件

Question

我已经开始学习 Java，并且在一个简单的程序中遇到问题，该程序应该将一些内容写入 numbers.dat 文件。

我面临两个问题:

1. 我得到的输出如下:

   2, 6, 12, 20, 30, 42, 56, 72, 90, 110, 132, 156, 182, 210, 240, 272, 306, 342, 380, 420, 462, 506, 552, 600, 650, 702, 756, 812, 870, 930, 992, 1056, 1122, 1190, 1260, 1332, 1406, 1482, 1560, 1640, 1722, 1806, 1892, 1980, 2070, 2162, 2256, 2352, 2450, 2550...

   什么时候应该是:

   对于偶数:

   2,4,6,8,10,12,14,……,98,100

   对于奇数:

   2,4,6,8,10,12,14,……,98,100,1,3,5,7,9,……..97,99

2. 我的第二个问题是输出没有写入 numbers.dat 文件!一切都是空白。

书中我试图解决的问题是:

Write a program called TextFileIO.java to create a file named numbers.dat. Then create an algorithm that writes all even numbered integers from 1 to 100, separated by a comma.

After the file has been created, close and reopen the file and display the results to the screen. After the results have been displayed append the odd number integers from 1 to 100, separated by a comma to the end of the file. Reopen the file and display the results. The contents of the file should be the even numbers from 1 to 100 separated by a comma followed by the odd number from 1 to 100 separated by a comma. The output of this program would be something like the following:

2,4,6,8,10,12,14,……,98,100

2,4,6,8,10,12,14,……,98,100,1,3,5,7,9,……..97,99

下面是我迄今为止尝试过的代码:

textFileIO.java

package package1;

import java.io.*;
import java.util.*;

//class definition
public class textFileIO{

    //The main function
    public static void main(String args[]) {

        //This declares a file to open.
        File outFile = new File("numbers.dat");

        int sumEven = 0;
        int sumOdd = 0;

        //File IO requires a try/catch block to prevent the program from crashing
        try {

            //a buffered writer is used to allow us to write to the file.
            BufferedWriter writer = new BufferedWriter(new FileWriter(outFile));

            //This for loop handles adding all of the numbers together
            for(int i = 1; i < 100; i += 2) {
                sumEven += i + 1;
                writer.write("" + sumEven + ", ");
            }

            //adding a new line and closing the file
            writer.newLine();
            writer.close();

            //A buffered Reader is used for reading a new file.
            BufferedReader reader = new BufferedReader(new FileReader(outFile));

            //Because I only add a new line at the end, I only need to read the first line.
            System.out.println(reader.readLine());

            //I need to write again, so I close the reader and open the writer.
            reader.close();

            //you need to create another object to append to the file
            //writer.open();
            BufferedWriter writer2 = new BufferedWriter(new FileWriter(outFile));

            //This for loop is identical to the previous one, except for odd numbers
            for(int i = 1; i < 100; i += 2) {
                sumOdd += i;
                writer2.write("" + sumOdd + ", ");
            }

            writer.newLine();
            writer.close();

            //The same here. You need to create another reader
            //reader.open();
            BufferedReader reader2 = new BufferedReader(new FileReader(outFile));
            System.out.println(reader2.readLine());

        }
        catch (Exception e) {

        }
    }
}

编辑2

我更改了代码，这是我的最新代码。我仍然遇到问题。控制台输出屏幕显示 49 和 50 作为输出，而我的numbers.dat 文件现在仅显示以逗号分隔的奇数列表。我现在做错了什么？

import java.io.*;
    import java.util.*;
    public class TextFileIO {
        public static void main(String[] args) throws Exception {
            //Clear the contents of numbers.dat if already exists and populated
            File fileOne = new File("numbers.dat");
            fileOne.delete();
            File newFile = new File("numbers.dat");
            newFile.createNewFile();
            //Create writer object
            PrintWriter writer = new PrintWriter(new FileWriter("numbers.dat"));
            //Loop from 1 to 100
            for (int i = 1; i <= 100; i++) {
                //If number is even, write to file  
                if (i % 2 == 0) {
                    writer.print(i + ",");
                }
            }
            //Close writer object.
            writer.close();
            //Read from file
            FileInputStream fileStream = new FileInputStream("numbers.dat");
            DataInputStream in = new DataInputStream(fileStream);
            BufferedReader reader = new BufferedReader(new InputStreamReader(in));
            //Print line
            System.out.println(reader.read());
            reader.close();
            //Write all odd numbers to file
            PrintWriter writer2 = new PrintWriter(new FileWriter("numbers.dat"));
            //Loop from 1 to 100
            for (int i = 1; i <= 100; i++) {
                //If number is odd, write to file  
                if (i % 2 == 1) {
                    writer2.print(i + ",");
                }
            }
            writer2.close();
            //Read from file
            FileInputStream fileStream2 = new FileInputStream("numbers.dat");
            DataInputStream in2 = new DataInputStream(fileStream2);
            BufferedReader reader2 = new BufferedReader(new InputStreamReader(in2));
            //Print line
            System.out.println(reader2.read());
            reader.close();
        }
     
     
    }

编辑3:我仍然无法获得所需的输出。我在控制台中得到的输出仍然是 49 和 50，并且在numbers.dat 文件中，输出仍然只是用逗号分隔的奇数。我无法理解我的代码到底要更改什么。

Answer 1

要打印正确的数字，您应该更改

偶数循环:

//This for loop handles adding all of the numbers together
for(int i = 2; i <=100; i += 2) {
writer.write("" + i + ", ");
}

奇数循环:

//This for loop is identical to the previous one, except for odd numbers
for(int i = 1; i < 100; i += 2) {
writer2.write("" + i + ", ");
}

并替换以下语句:

System.out.println(reader.read());

与

System.out.println(reader.readLine());

你应该完成了。

编辑

public class textFileIO {
    public static void main(String[] args) throws Exception {
        //Clear the contents of numbers.dat if already exists and populated
        File fileOne = new File("numbers.dat");
        fileOne.delete();
        File newFile = new File("numbers.dat");
        newFile.createNewFile();
        //Create writer object
        PrintWriter writer = new PrintWriter(new FileWriter("numbers.dat"));
        //Loop from 1 to 100
        for (int i = 1; i <= 100; i++) {
            //If number is even, write to file  
            if (i % 2 == 0) {
                writer.print(i + ",");
            }
        }
        //Close writer object.
        writer.close();
        //Read from file
        FileInputStream fileStream = new FileInputStream("numbers.dat");
        DataInputStream in = new DataInputStream(fileStream);
        BufferedReader reader = new BufferedReader(new InputStreamReader(in));
        //Print line
        System.out.println(reader.readLine());
        reader.close();
        //Write all odd numbers to file
        PrintWriter writer2 = new PrintWriter(new FileWriter("numbers.dat"));
        //Loop from 1 to 100
        for (int i = 1; i <= 100; i++) {
            //If number is odd, write to file  
            if (i % 2 == 1) {
                writer2.print(i + ",");
            }
        }
        writer2.close();
        //Read from file
        FileInputStream fileStream2 = new FileInputStream("numbers.dat");
        DataInputStream in2 = new DataInputStream(fileStream2);
        BufferedReader reader2 = new BufferedReader(new InputStreamReader(in2));
        //Print line
        System.out.println(reader2.readLine());
        reader.close();
    }
}

这对我来说非常有效，这是输出......

2,4,6,8,10,12,14,16,18,20,22,24,26,28,30,32,34,36,38,40,42,44,46,48,50,52,54,56,58,60,62,64,66,68,70,72,74,76,78,80,82,84,86,88,90,92,94,96,98,100, 1,3,5,7,9,11,13,15,17,19,21,23,25,27,29,31,33,35,37,39,41,43,45,47,49,51,53,55,57,59,61,63,65,67,69,71,73,75,77,79,81,83,85,87,89,91,93,95,97,99,