Java - InputStream Class

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Introduction

The Java InputStream class is the superclass of all classes representing an input stream of bytes. Applications that need to define a subclass of InputStream must always provide a method that returns the next byte of input.

Class declaration

Following is the declaration for Java.io.InputStream class −

 public abstract class InputStream extends Object implements Closeable

Class constructors

Sr.No. Constructor & Description
1

InputStream()

Single Constructor

Class methods

Sr.No. Method & Description
1 int available()

This method returns an estimate of the number of bytes that can be read (or skipped over) from this input stream without blocking by the next invocation of a method for this input stream.
2 void close()

This method closes this input stream and releases any system resources associated with the stream.
3 void mark(int readlimit)

This method marks the current position in this input stream.
4 boolean markSupported()

This method tests if this input stream supports the mark and reset methods.
5 abstract int read()

This method reads the next byte of data from the input stream.
6 int read(byte[] b)

This method reads some number of bytes from the input stream and stores them into the buffer array b.
7 int read(byte[] b, int off, int len)

This method reads up to len bytes of data from the input stream into an array of bytes.
8 void reset()

This method repositions this stream to the position at the time the mark method was last called on this input stream.
9 long skip(long n)

This method skips over and discards n bytes of data from this input stream.

Methods inherited

This class inherits methods from the following classes −

  • Java.io.Object

Example - Using close() with FileInputStream (Automatic Closure with Try-With-Resources)

The following example shows the usage of Java InputStream close() method.

InputStreamDemo.java

 package com.tutorialspoint; import java.io.FileInputStream; import java.io.IOException; import java.io.InputStream; public class InputStreamDemo { public static void main(String[] args) { try (InputStream inputStream = new FileInputStream("example.txt")) { int data; while ((data = inputStream.read()) != -1) { // Read character by character System.out.print((char) data); } // No need to manually close, try-with-resources handles it } catch (IOException e) { e.printStackTrace(); } } }

Output(if example.txt contains "Hello")

Let us compile and run the above program, this will produce the following result−

 Hello

Explanation

  • Uses FileInputStream, a subclass of InputStream, to read "example.txt".

  • Reads characters one at a time and prints them.

  • Uses try-with-resources, which automatically calls close() at the end.

Example - Using mark(int readLimit) with BufferedInputStream

The following example shows the usage of Java InputStream mark(int readLimit) method.

InputStreamDemo.java

 package com.tutorialspoint; import java.io.BufferedInputStream; import java.io.FileInputStream; import java.io.IOException; import java.io.InputStream; public class InputStreamDemo { public static void main(String[] args) { try (InputStream inputStream = new BufferedInputStream(new FileInputStream("example.txt"))) { System.out.println("Mark supported? " + inputStream.markSupported()); // Read and print first character System.out.print((char) inputStream.read()); // Mark the current position inputStream.mark(5); // Can read up to 5 bytes before mark expires // Read next two characters System.out.print((char) inputStream.read()); System.out.print((char) inputStream.read()); // Reset back to the marked position inputStream.reset(); // Read again from the marked position System.out.print((char) inputStream.read()); System.out.print((char) inputStream.read()); } catch (IOException e) { e.printStackTrace(); } } }

Output(if example.txt contains "Hello")

Let us compile and run the above program, this will produce the following result−

 Mark supported? true Helo elo

Explanation

  • Uses BufferedInputStream, which supports marking.

  • Marks the position after reading one character.

  • Reads two more characters.

  • Resets to the marked position.

  • Reads again from the marked position.

Example - Checking markSupported() for BufferedInputStream

The following example shows the usage of Java InputStream markSupported() method.

InputStreamDemo.java

 package com.tutorialspoint; import java.io.BufferedInputStream; import java.io.FileInputStream; import java.io.IOException; import java.io.InputStream; public class InputStreamDemo { public static void main(String[] args) { try (InputStream inputStream = new BufferedInputStream(new FileInputStream("example.txt"))) { System.out.println("Mark supported? " + inputStream.markSupported()); inputStream.mark(5); // Mark the position System.out.print((char) inputStream.read()); // Read a character System.out.print((char) inputStream.read()); // Read another character inputStream.reset(); // Reset back to the mark System.out.print((char) inputStream.read()); // Read again } catch (IOException e) { e.printStackTrace(); } } }

Output(if example.txt contains "Java")

Let us compile and run the above program, this will produce the following result−

 Mark supported? true Jav

Explanation

  • Uses BufferedInputStream, which supports marking.

  • Calls markSupported(), which returns true.

  • Marks a position, reads characters, and resets to the mark.

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