java - 文件的输入/输出

Question

我为我的一个类(class)编写了一个简短的程序，但有些东西我无法弄清楚。所以我应该在文件中写入 100 个随机整数，读回数据并按升序打印整数。一切正常，但我在输出文件上看不到最终的排序列表，任何人都可以看到为什么吗？

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，非常感谢您的帮助!

Answer 1

使用 Scanner input = new Scanner(file); 读取文件时，文件为空

在打印值后使用output.flush()保存数据。

output.close() - 将关闭您的流，并且您将无法存储排序后的值。

// 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();