[Java] How to use FileReader class and BufferedReader class

Programming study diary

November 16, 2020 The usage of FileReader class and BufferedReader class is summarized again.

What is the FileReader class?

It is an API for reading a text file, and is used to perform processing based on the contents of the text file. The characters in the file are read in a stream of characters that can read and write data character by character. The FileReader class has only a read method that reads characters one by one, so if you want to read data in a stream of bytes that can be read and written in byte units, use the FileInputStream class.

Read character by character with read method

import java.io.File;
import java.io.FileReader;
import java.io.IOException;
 
public class Main {
 
    public static void main(String[] args) {
        try {
            //Specify the file path as an argument of the File class constructor
            File file = new File("text.txt");
         
            //Exception handling when the file does not exist
            //The exists method returns true if the file exists, false if it does not exist
            if (!file.exists()) {
                System.out.print("File does not exist");
                return;
            }
         
            //Read and display character by character using FileReader class and read method
            FileReader fileReader = new FileReader(file);
            int data;
            //Repeat until the end of the file
            while ((data = fileReader.read()) != -1) {
                //Cast the read character to char type and display the character
                System.out.print((char) data);
            }
         
            //Finally close the file to free resources
            fileReader.close();
         
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
 
}

What is the BufferedReader class?

Like the FileReader class, it is a class that reads text files, and the methods provided are different from the FileReader class. The BufferReader class provides a readline method that reads line by line. The FileReader class reads one character at a time, but if the number of characters is large, it may become inefficient, so decide a certain amount of memory and issue a read command to the OS when it accumulates. This is called buffering.

Read line by line with the readline method

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
 
public class Main {
 
    public static void main(String[] args) {
        try {
            //Specify the file path as an argument of the File class constructor
            File file = new File("c:SampleTest.txt");
         
            //Exception handling when the file does not exist
            //The exists method returns true if the file exists, false if it does not exist
            if (!file.exists()) {
                System.out.print("File does not exist");
                return;
            }
         
            //Read and display line by line using the readLine method of the BufferedReader class
            FileReader fileReader = new FileReader(file);
            BufferedReader bufferedReader = new BufferedReader(fileReader);
            String data;
            //Repeat until the end of the file
            while ((data = bufferedReader.readLine()) != null) {
                System.out.println(data);
            }
         
            //Finally close the file to free resources
            bufferedReader.close();
         
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
 
}

References

Class BufferedReader Class FileReader [Java] Read text files with FileReader and BufferedReader