java - 检查该行是否是文本文档中的最后一行

Question

我正在尝试检查是否已到达文本文档中的最后一行，以便在文本文档中写入简单的行。

我尝试了下面的代码，但收到此错误:

Exception in thread "main" java.util.NoSuchElementException: No line found

我在 hello.txt 文档中有文本，所以我不明白这个错误的含义。

我该如何解决这个问题？

感谢任何帮助。

代码:

public static void main(String[] args) {
    try (PrintWriter writer = new PrintWriter("D:\\hl_sv\\hello2.txt");

    Scanner scanner = new Scanner("D:\\hl_sv\\hello.txt")) {

        while (scanner.hasNextLine()) {
            String line = scanner.nextLine();

            // In the case the line is the last one and there is no number.
            // The content of the arrayList must be printed.
            if ((line = scanner.nextLine()).isEmpty()) {
                System.out.println("last line in the text document");
                writer.write("last line in the text document.");
            }

        }
    } catch (FileNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

}

编辑

public static void main(String[] args) {
    try (PrintWriter writer = new PrintWriter("D:\\hl_sv\\hello2.txt");

            Scanner scanner = new Scanner("D:\\hl_sv\\hello.txt")) {
                while (scanner.hasNextLine()) {
                    String line = scanner.nextLine();

                    // In the case the line is the last one and there is no number.
                    // The content of the arrayList must be printed.
                    if (line.isEmpty()) { // <-- Removed  = scanner.nextLine()
                        System.out.println("last line in the text document");
                        writer.write("last line in the text document.");
                    }else{
                        writer.write(line);
                    }

                }
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            }
    }

使用编辑代码，我不再收到错误，但我在文本文档 hello2.txt 中打印了 D:\hl_sv\hello.txt 行？

Answer 1

已更新

我在我的计算机上尝试了这段代码，根据您的规范，它工作正常。

这是我的代码:

import java.io.File;
import java.io.FileNotFoundException;
import java.io.PrintWriter;
import java.util.Scanner;

class Test {

    public static void main(String[] args) {
        try {

            PrintWriter writer = new PrintWriter(new File(
                    "../Test/src/com/hello2.txt"));

            Scanner scanner = new Scanner(new File("../Test/src/com/hello.txt"));
            while (scanner.hasNextLine()) {
                String line = scanner.nextLine()+"\n";
                System.out.println(line);
                writer.write(line);
            }

            System.out.println("last line in the text document");
            writer.write("last line in the text document.");
            scanner.close();
            writer.close();
        } catch (FileNotFoundException e) {
            System.out.println(e);
        }
    }
}

已编辑

您应该添加新文件

new PrintWriter(new File("D:\\hl_sv\\hello2.txt"));

和

new Scanner(new File("D:\\hl_sv\\hello.txt"))); 

因为PritWriter需要File作为参数，而Scanner需要String或File作为论证。由于您在 Scanner ( "D:\\hl_sv\\hello.txt") 中仅使用 String ，因此您得到了“D:\hl_sv\hello.txt” hello2.txt 文件中的行。

并且您可以使用在主函数之后立即声明的 line 变量来访问主类中的 line 变量。

所以你的代码应该是:

public static void main(String[] args) {
    String line="";

    try (PrintWriter writer = new PrintWriter(new File("D:\\hl_sv\\hello2.txt"));

    Scanner scanner = new Scanner(new File("D:\\hl_sv\\hello.txt"))) {

        while (scanner.hasNextLine()) {
            line = scanner.nextLine();

            // In the case the line is the last one and there is no number.
            // The content of the arrayList must be printed.

        }

        System.out.println("last line in the text document");
        writer.write("last line in the text document.");
    } catch (FileNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

}

您可以通过非常简单的方式检查该文本文件的最后一行/逻辑只需在 while 循环之后执行您的操作。因为在代码中的 while 循环之后，文本文件中没有任何行。

public static void main(String[] args) {
    try (PrintWriter writer = new PrintWriter(new File("D:\\hl_sv\\hello2.txt"));

    Scanner scanner = new Scanner(new File("D:\\hl_sv\\hello.txt"))) {

        while (scanner.hasNextLine()) {
            String line = scanner.nextLine();

            // In the case the line is the last one and there is no number.
            // The content of the arrayList must be printed.

        }

        System.out.println("last line in the text document");
        writer.write("last line in the text document.");
    } catch (FileNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

}

当您使用此声明时

if ((line = scanner.nextLine()).isEmpty())

扫描仪找不到任何行(在文件末尾之后)，因此不存在这样的元素(下一行)，因此出现此异常

Exception in thread "main" java.util.NoSuchElementException: No line found