java io练习题_练习 Java类IO流练习题

1. 编写程序从文件中读取数据，并输出到控制台。

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

public class ReadFromFile {

    public static void main(String[] args) {
        try {
            File file = new File("data.txt");
            Scanner scanner = new Scanner(file);
            while (scanner.hasNextLine()) {
                System.out.println(scanner.nextLine());
            }
            scanner.close();
        } catch (FileNotFoundException e) {
            System.out.println("File not found.");
        }
    }
}

2. 编写程序从控制台读取数据，并将数据写入文件。

import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.util.Scanner;

public class WriteToFile {

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter data: ");
        String data = scanner.nextLine();
        scanner.close();

        try {
            File file = new File("output.txt");
            FileWriter writer = new FileWriter(file);
            writer.write(data);
            writer.close();
        } catch (IOException e) {
            System.out.println("Error writing to file.");
        }
    }
}

3. 编写程序从一个文件中复制数据到另一个文件。

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;

public class CopyFile {

    public static void main(String[] args) {
        try {
            File inputFile = new File("input.txt");
            File outputFile = new File("output.txt");

            FileInputStream inputStream = new FileInputStream(inputFile);
            FileOutputStream outputStream = new FileOutputStream(outputFile);

            byte[] buffer = new byte[1024];
            int length;
            while ((length = inputStream.read(buffer)) != -1) {
                outputStream.write(buffer, 0, length);
            }

            inputStream.close();
            outputStream.close();
        } catch (FileNotFoundException e) {
            System.out.println("File not found.");
        } catch (IOException e) {
            System.out.println("Error copying file.");
        }
    }
}

4. 编写程序读取一个目录下的所有文件，并输出文件名和文件大小。

import java.io.File;

public class ListFiles {

    public static void main(String[] args) {
        File directory = new File(".");

        File[] files = directory.listFiles();
        for (File file : files) {
            if (file.isFile()) {
                System.out.println(file.getName() + " (" + file.length() + " bytes)");
            }
        }
    }
}