Java uses the readLine() function of the InputStreamReader class to read the file content line by line

Java uses the readLine() function of the InputStreamReader class to read file content line by line

In Java, we often need to read content from files. If you need to read the file content line by line, you can use the readLine() function of the InputStreamReader class. This article will introduce how to use the readLine() function to read file contents line by line and provide code examples.

1. Introduction to InputStreamReader class

InputStreamReader is a character stream input class in Java, which inherits from the Reader class. It can read bytes from an InputStream and decode them into characters. The constructor of InputStreamReader can specify the character set encoding to convert bytes into characters.

2. How to use the readLine() function

readLine() is a function in the InputStreamReader class, used to read file contents line by line. It is defined as follows:

public String readLine() throws IOException

This function returns the next line of the file, and the return result is a string type. If the end of the file has been reached, null is returned. This function throws IOException.

3. Code example for reading file content line by line

The following is a code example for reading file content line by line using the readLine() function of the InputStreamReader class:

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

public class ReadFileByLine {
    public static void main(String[] args) {
        String fileName = "test.txt"; // 文件名
        
        try (BufferedReader br = new BufferedReader(new FileReader(fileName))) {
            String line;
            while ((line = br.readLine()) != null) {
                System.out.println(line);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

In the above code, first we define a file name fileName to specify the file to be read. We then wrapped a FileReader with a BufferedReader, converted the file stream to a character stream, and created a BufferedReader object br. Next, we use a while loop to read the file contents line by line until the end of the file (readLine() returns null). In the loop, we print the contents of each line through System.out.println(line).

It is worth noting that in the try code block, we use the try-with-resources statement introduced in Java 7 to handle the closing operation of the IO stream. This automatically closes the file stream at the end of the code without having to manually call the close() function.

4. Summary

By using the readLine() function of the InputStreamReader class, we can easily read the file content line by line. The code example above shows how to use this function to read a file and print each line of the file. Using this method can help us better handle large files and process the contents of the file line by line.

By reading this article, you should be able to master the method of reading file content line by line using the readLine() function of the InputStreamReader class, and you can make further adjustments and extensions as needed. Good luck with your file reading tasks!

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