Java InputStream Class

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

Since InputStream is an abstract class, it is not useful by itself. 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.

Create an InputStream

In order to create an InputStream, we must import the java.io.InputStream package first. Once we import the package, here is how we can create the input stream.

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

Here, we have created an input stream using FileInputStream. It is because InputStream is an abstract class. Hence we cannot create an object of InputStream.

Methods of InputStream

The InputStream class provides different methods that are implemented by its subclasses. Here are some of the commonly 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;

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: 39
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).