Question

我为我的一个班级写了一个简短的程序，有些东西是我无法弄清楚的。所以我应该在一个文件上写100个随机整数，读回数据并按递增顺序打印整数。一切正常，但我没有在输出文件中看到我的最终排序列表，任何人都可以看到原因？

这是我的代码：

private final static int NUMBEROFRANDOM = 100;

public static void main(String[] args) throws IOException {

    // Creating my file
    java.io.File file = new java.io.File("Question1.txt");

    // If it already exists, print a message and terminate program
    if (file.exists()) {
        System.out.println("File already exists.");
        System.exit(0);
    }

    // Creating my PrintWriter object
    PrintWriter output = new PrintWriter(file);

    // Creating 100 random numbers between 0 and 100 and printing them on the file
    for (int i = 0; i < NUMBEROFRANDOM; i++) {
        int number = (int) (Math.random() * 101);
        output.print(number + " ");
    }

    // Creating my Scanner object
    Scanner input = new Scanner(file);

    // Creating my array list to store the sorted list of 100 elements
    ArrayList<Integer> sortedList = new ArrayList<Integer>();

    // Reading the elements from the file and adding them into my array list
    while (input.hasNext()) {
        sortedList.add(input.nextInt());
    }

    //Sorting elements from array list
    Collections.sort(sortedList);

    // Printing the elements in increasing order
    for (int i = 0; i < sortedList.size(); i++) {
        //System.out.println(sortedList.get(i));
        output.print(sortedList.get(i));
    }

    // Closing my objects
    input.close();
    output.close();

}

非常感谢，非常感谢任何帮助！

Answer 1

使用Scanner input = new Scanner(file);

阅读文件时，您的文件为空

打印值后，使用output.flush()保存数据。

output.close() - 将关闭您的信息流，但您将无法存储已排序的值。

// Creating 100 random numbers between 0 and 100 and printing them on the file
for (int i = 0; i < NUMBEROFRANDOM; i++) {
    int number = (int) (Math.random() * 101);
    output.print(number + " ");
}

output.flush();

Answer 2

您需要关闭输出流才能将其写入文件。你第二次正确地这样做了，但不是第一次。

添加：

output.close();

后：

// Creating 100 random numbers between 0 and 100 and printing them on the file
 for (int i = 0; i < NUMBEROFRANDOM; i++) {
     int number = (int) (Math.random() * 101);
    output.print(number + " ");
 }
//Here close the first output stream to get the data to the file.
output.close();

Answer 3

在下面的代码行之前，您需要close或flush将您的内容写入您的文件。

output.close(); <--- you need to close here
Scanner input = new Scanner(file);

因为，直到上面的代码行，没有任何内容写入文件。所以，下面的代码变得无用

while (input.hasNext()) {  // nothing to read
        sortedList.add(input.nextInt()); //nothing added to List
    }

    //Sorting elements from array list
    Collections.sort(sortedList);  //nothing to sort

    // Printing the elements in increasing order
    for (int i = 0; i < sortedList.size(); i++) { 

        output.print(sortedList.get(i)); // won't execute this line
    }

文件的输入/输出

3 个答案: