Java InputStream Class

In this tutorial, we will learn about the Java InputStream class and its methods with the help of an example.

The InputStream class of the java.io package is an abstract superclass that represents an input stream of bytes.

Since InputStream is a theoretical class, it isn’t useful without anyone else. However, its subclasses can be used to read data.

---

Subclasses of InputStream

In order to use the functionality of InputStream, we can use its subclasses. Some of them are:

• FileInputStream
• ByteArrayInputStream
• ObjectInputStream

• 

We will learn about all these subclasses in the next tutorial.

---

Make an InputStream

To make an InputStream, we should import the java.io.InputStream package first. When we import the package, here is the way we can make the input stream.

// Creates an InputStream
InputStream object1 = new FileInputStream();

Here, we have made an input stream using FileInputStream. It is on the grounds that InputStream is an abstract class. Consequently, we can’t make an object of InputStream.

Note: We can likewise make an input stream from different subclasses of InputStream.

---

Methods of InputStream

The InputStream class gives various strategies that are actualized by its subclasses. Here is a portion of the regularly used methods:

• read() – reads one byte of data from the input stream
• read(byte[] array) – reads bytes from the stream and stores in the specified array
• available() – returns the number of bytes available in the input stream
• mark() – marks the position in the input stream up to which data has been read
• reset() – returns the control to the point in the stream where the mark was set
• markSupported() – checks if the mark() and reset() method is supported in the stream
• skips() – skips and discards the specified number of bytes from the input stream
• close() – closes the input stream

---

Example: InputStream Using FileInputStream

Here is how we can implement InputStream using the FileInputStream class.

Suppose we have a file named input.txt with the following content.

This is a line of text inside the file.

Let’s try to read this file using FileInputStream (a subclass of InputStream).

import java.io.FileInputStream;
import java.io.InputStream;

public class Main {
    public static void main(String args[]) {

        byte[] array = new byte[100];

        try {
            InputStream input = new FileInputStream("input.txt");

            System.out.println("Available bytes in the file: " + input.available());

            // Read byte from the input stream
            input.read(array);
            System.out.println("Data read from the file: ");

            // Convert byte array into string
            String data = new String(array);
            System.out.println(data);

            // Close the input stream
            input.close();
        }
        catch (Exception e) {
            e.getStackTrace();
        }
    }
}

Output

Available bytes in the file: 35
Data read from the file:
This is a line of text inside the file

In the above example, we have created an input stream using the FileInputStream class. The input stream is linked with the file input.txt.

InputStream input = new FileInputStream("input.txt");

To read data from the input.txt file, we have implemented these two methods.

input.read(array);      // to read data from the input stream
input.close();             // to close the input stream

To learn more, visit Java InputStream (official Java documentation).

---

Thanks for reading! We hope you found this tutorial helpful and we would love to hear your feedback in the Comments section below. And show us what you’ve learned by sharing your photos and creative projects with us.

Java I/O Streams