The Java.io.InputStream class is the superclass of all classes representing an input stream of bytes. How is it reading a file with characters?

I have a file named mark_method.json containing ABCDE in it and I am reading this file using the InputStream class.

By definition, the InputStream class reads an input stream of bytes. How does this work? I don't have bytes in the file, but characters?

I am trying to understand how a stream reading bytes is reading characters from the file?

public class MarkDemo {
    public static void main(String args[]) throws Exception {
	    InputStream is = null;
	
	    try {
		    is = new FileInputStream("C:\\Users\\s\\Documents\\EB\\EB_02_09_2020_with_page_number_and_quote_number\\Old_images\\mark_method.json");
	    }
	    catch(Exception e) {
		    e.printStackTrace();
	    } finally {
		    if(is != null) {
			    is.close();
		    }
	    }
    }
}

Every data on the computer is stored in bits and bytes. Here the content of the files is also stored in bytes.

We have programs which convert these bytes into human-readable forms thus we see the mark_method.json file containing characters and not bytes.

An character is a byte. (At least in ASCII).
Each byte from 0 to 127 has a character value. For example 0 is the Null-character, 0xa is \n, 0xd is \r, 0x41 is 'A' and so on.

The implementation only knows bytes. It doesn't know, that the char 0x2709 is ✉. It only sees it as two bytes: 0x27 and 0x09.
Only the texteditor interprets the bytes and show the matching symbol/letter

I think what you are actually asking here is how to convert the bytes you read from file using FileInputStream in to a Java String object you can print and manipulate.

FileInputStream does not have any read methods for directly producing a String object so if that is what you want, you need to further manipulate the input you get.

Option one is to use the Scanner class:

Scanner scanner = new Scanner(is);
String word = scanner.next();

Another option is to read the bytes and use the constructor of the String class that works with byte array:

byte [] bytes = new byte[10];
is.read(bytes);
String text = new String(bytes);

Note that for simplicity I just assumed you can read 10 valid bytes from your file.
In real code you would need some logic to make sure you are reading correct number of bytes.

Also, if your file is not stored using your system default character set, you will need to specify the character set as a parameter to the String constructor.

Finally, you can use another wrapper class, BufferedReader that has a readLine function which takes care of all the logic needed to read bytes representing a line of text from a file and return them in a String.

BufferedReader in = new BufferedReader(new FileReader("foo.in"));
String line = in.readLine();