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Showing content from https://www.tutorialspoint.com/java/io/java_io_fileinputstream.htm below:

Java - FileInputStream Class

The Java FileInputStream class obtains input bytes from a file in a file system. What files are available depends on the host environment. Following are the important points about FileInputStream −

• This class is meant for reading streams of raw bytes such as image data.

• For reading streams of characters, use FileReader.

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

public class FileInputStream
   extends InputStream

FileInputStream(File file)

This creates a FileInputStream by opening a connection to an actual file, the file named by the File object file in the file system.

FileInputStream(FileDescriptor fdObj)

This creates a FileInputStream by using the file descriptor fdObj, which represents an existing connection to an actual file in the file system.

FileInputStream(String name)

This creates a FileInputStream by opening a connection to an actual file, the file named by the path name name in the file system.

This method returns an estimate of the number of remaining 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.

This method closes this file input stream and releases any system resources associated with the stream.

This method ensures that the close method of this file input stream is called when there are no more references to it.

This method returns the unique FileChannel object associated with this file input stream.

This method returns the FileDescriptor object that represents the connection to the actual file in the file system being used by this FileInputStream.

This method reads a byte of data from this input stream.

This method reads up to b.length bytes of data from this input stream into an array of bytes.

This method reads up to len bytes of data from this input stream into an array of bytes.

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

This class inherits methods from the following classes −

• Java.io.InputStream
• Java.io.Object

The following example shows the usage of Java FileInputStream available() method.

package com.tutorialspoint;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;

public class FileInputStreamDemo {
   public static void main(String[] args) {
      File file = new File("example.txt");

      try (FileInputStream fis = new FileInputStream(file)) {
         // Get the number of available bytes at the beginning
         int availableBytes = fis.available();
         System.out.println("Bytes available to read: " + availableBytes);
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

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

Bytes available to read: 50

• A FileInputStream is created for "example.txt".

• The available() method is called before reading any data.

• The program prints the number of bytes available to be read.

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

package com.tutorialspoint;

import java.io.FileInputStream;
import java.io.IOException;

public class FileInputStreamDemo {
   public static void main(String[] args) {
      try {
         FileInputStream fis = new FileInputStream("example.txt"); // Open file

         int data;
         while ((data = fis.read()) != -1) { // Read file byte by byte
            System.out.print((char) data);
         }

         fis.close(); // Close stream after reading
         System.out.println("\nFile closed successfully.");

      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

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

Hello
File closed successfully.

• FileInputStream is opened to read example.txt.

• Data is read byte by byte using read().

• close() method is called, after reading to release resources.

• If close() is not called, it may cause memory leaks or prevent other processes from accessing the file.

The following example shows the usage of Java FileInputStream getFD() method.

package com.tutorialspoint;

import java.io.FileDescriptor;
import java.io.FileInputStream;
import java.io.IOException;

public class FileInputStreamDemo {
   public static void main(String[] args) {
      try (FileInputStream fis = new FileInputStream("example.txt")) {
         FileDescriptor fd = fis.getFD(); // Get file descriptor

         if (fd.valid()) {
            System.out.println("The file descriptor is valid.");
         } else {
            System.out.println("The file descriptor is not valid.");
         }

      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

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

The file descriptor is valid.

• Open FileInputStream for "example.txt".

• Retrieve the file descriptor using getFD().

• Check if the file descriptor is valid using fd.valid().

• Print whether the file descriptor is valid or not.

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