打开文件并存储消息。将消息读入字符串变量进行打印。 Java / Netbeans

Question

嘿，我正在进行的这项练习需要一些帮助。我必须打开一个名为hello.txt的文件，然后存储消息“ Hello World！”。在文件中。然后，我必须关闭文件并打开它，然后将消息读入字符串变量以进行打印。到目前为止，我的代码如下。您对我如何成功编译此代码有任何建议吗？

package ProgrammingExercise11;

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

public class Input {

    public static void main(String[] args) throws FileNotFoundException
    {
        Scanner in = new Scanner(System.in);
        File inputFile = new File(hello.txt);
        Scanner in = new Scanner(inputFile);
        PrintWriter out = new PrintWriter(hello.txt);
        out.println("Hello, World!");
        String line = in.nextLine();
        in.close();
        out.close();
    }

}

Answer 1

好，让我们回答您的问题。

Scanner in = new Scanner(System.in);
        File inputFile = new File(hello.txt);
        Scanner in = new Scanner(inputFile);
        PrintWriter out = new PrintWriter(hello.txt);
        out.println("Hello, World!");
        String line = in.nextLine();
        in.close();
        out.close();

您的代码未编译，因为您引入了两个具有相同名称in的变量，而未声明hello.txt。按照您的想法解决。

 public static void main(String[] args) throws Exception {
            String filePath = "hello.txt";
            File inputFile = new File(filePath);

            PrintWriter printWriter = new PrintWriter(inputFile);
            printWriter.write("Hello World!");
            printWriter.close();

            InputStream is = new FileInputStream(inputFile.getPath());
            BufferedReader buf = new BufferedReader(new InputStreamReader(is));
            String line = buf.readLine();
            System.out.println(line);

            is.close();
            buf.close();

    }

欢迎来到Java世界！

Answer 2

自Java 7以来的Files类提供了对文件，目录或其他类型的文件进行操作的静态方法，这更加简单和灵活。

String file = "hello.txt";
Path filePath = Paths.get(file);
if (Files.isRegularFile(filePath)) {
    try(OutputStream fos = new FileOutputStream(file);
        InputStream fis = new FileInputStream(file)){
        // write message to file.
        String message = "Hello World!";
        byte[] messageBytes = message.getBytes();
        fos.write(messageBytes);

        // read message from file.
        byte[] receivedBytes = new byte[fis.available()];
        fis.read(receivedBytes);
        System.out.println(new String(receivedBytes));
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
}