How does Java I/O stream perform string operations?

Java I/O streams provide Reader and Writer classes to process string data. Reader is used to read text from a character input stream. Single characters can be read using the read() method. Writer is used to write text to a character output stream. Text can be written using the write() method.

String operations in Java I/O streams

Java I/O streams provide powerful functions for processing characters String data. By using the Reader and Writer classes, you can conveniently read strings from a variety of sources and write to a variety of destinations.

Reader

Reader class is used to read text data from a character input stream. You can use the following methods to process strings:

// 从 FileInputStream 中读取字符串
try (InputStreamReader reader = new InputStreamReader(new FileInputStream("input.txt"))) {
    StringBuilder sb = new StringBuilder();
    int c;
    while ((c = reader.read()) != -1) {
        sb.append((char) c);
    }
    String text = sb.toString();
} catch (IOException e) {
    e.printStackTrace();
}

Writer

Writer class is used to write text data to a character output stream. You can use the following methods to process strings:

// 向 FileWriter 中写入字符串
try (FileWriter writer = new FileWriter("output.txt")) {
    String text = "Hello, world!";
    writer.write(text);
    writer.flush();
} catch (IOException e) {
    e.printStackTrace();
}

Practical case: reading and writing strings from files

Consider a scenario: You have a Text file input.txt, which contains some text. You want to read the contents of the file and copy the contents into another text file output.txt.

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

class FileCopy {
    public static void main(String[] args) {
        try {
            // 从 input.txt 中读取
            File inputFile = new File("input.txt");
            FileReader reader = new FileReader(inputFile);
            BufferedReader bufferedReader = new BufferedReader(reader);

            // 向 output.txt 中写入
            File outputFile = new File("output.txt");
            FileWriter writer = new FileWriter(outputFile);

            String line;
            while ((line = bufferedReader.readLine()) != null) {
                writer.write(line + "\n");
            }

            reader.close();
            writer.close();
            System.out.println("文件已复制完成。");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

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