修改

Question

我已经开始学习Java，并且遇到了一个简单程序的问题，该程序应该将一些内容写入numbers.dat文件。

我面临两个问题：

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 ，650,702,756,812,870,930,992,1056,1122,1190,1260,1332,1402,1482,1560,1640,1722,1806,1892,1980,2070,2162,2256,2352,2450 ，2550 ......

应该是：

对于偶数：


2,4,6,8,10,12,14，......，98100

对于奇数：


2,4,6,8,10,12,14，......，98,100,1,3,5,7,9，......。.97,99
我的第二个问题是输出没有写入numbers.dat文件！这一切都是空白的。

请有人帮我这个。我真的很感激

我试图解决的书中的问题是：

编写一个名为TextFileIO.java的程序来创建一个名为numbers.dat的文件。然后创建一个算法，将所有偶数编号的整数从1写入100，用逗号分隔。

创建文件后，关闭并重新打开文件并将结果显示在屏幕上。显示结果后，将奇数整数从1添加到100，用逗号分隔到文件末尾。重新打开文件并显示结果。该文件的内容应为1到100之间的偶数，用逗号分隔，后跟以逗号分隔的1到100的奇数。该程序的输出类似于以下内容：

2,4,6,8,10,12,14，......，98100

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

以下是我到目前为止尝试过的代码：

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) {

        }
    }
}

修改2

我更改了代码，这是我最新的代码。我还有问题。控制台输出屏幕显示49和50作为out put annnd我的numbers.dat文件现在只显示逗号分隔列表f奇数...我现在做错了什么？ :(请帮帮我！

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：伙计我仍然无法获得所需的输出。我仍然在控制台中获得49和50的输出，而在numbers.dat文件中，输出仍然是由逗号分隔的ONLy奇数。我无法理解我的代码究竟要改变什么：（

Answer 1

要打印正确的号码，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 + ", ");
}

奇数圈：

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

并替换以下声明：

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

与

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

你应该完成。

修改

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();
    }
}

这对我来说非常合适，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，

Answer 2

一些事情：

对于第二个writer（writer2），您需要在FileWriter构造函数中传入一个“true”值。否则，它只会用新内容覆盖outfile（参见FileWriter Constructor）

PrintWriter writer2 = new PrintWriter（new FileWriter（“numbers.dat”，true ））;
正如Govan所说，你不是在关闭writer2。这就是您的文件为空的原因。如果调用writer2.close，则调用BufferedWriter的“flush”方法。 “flush”实际上是强制写入者将数据写入文件（When to Flush a BufferedWriter）。
正如Bharat所说，你应该重新编写你的循环来使用“i”变量来写，而不是sumEven。你编写sumEven的方式，你会得到以下结论：

i = 1，sumEven = sumEven + i + 1 = 0 + 1 + 1 = 2

i = 3，sumEven = sumEven + i + 1 = 2 + 3 + 1 = 6

i = 5，sumEven = sumEven + i + 1 = 6 + 5 + 1 = 12

...

Answer 3

你的第一个循环可以是这样的

for (i = 0; i < 100 ; i+2)
{ 
   if (i != 0) {
    writer.print(", ");
   } 
    writer.print(i+2);
}

第二个应该是这样的

for (i = 0; i < 100 ; i+2)
{ 
    writer.print( ", " +(i+1));
}

否则你必须在行尾添加额外的逗号！

Answer 4

我对您的代码进行了一些更改。

首先你不需要两个作家，也不需要两个读者。

由于您只写一个文件，因此您的单个编写者可以编写偶数和奇数。我将考虑两个编写器的情况是，如果您同时单独编写奇数文件和偶数文件。

无论如何，我只是评论了绒毛的东西。如果删除所有注释，代码应该更简单，更有效，最可读。

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.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) {
                    writer.print(i + ",");
                }
            }
            writer.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());
            reader2.close();
        }


    }

稍微清理一下代码，你得到以下内容

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 + ",");
            }
        }
        //Loop from 1 to 100
        for (int i = 1; i <= 100; i++) {
            //If number is odd, write to file  
            if (i % 2 == 1) {
                writer.print(i + ",");
            }
        }
        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();
    }
}

将偶数和奇数写入dat文件

4 个答案:

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