Java - FilterInputStream available() method

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Description

The Java FilterInputStream available() method returns an estimate of the number of bytes that can be read from this input stream without blocking by the next invoker of a method for this input stream.

Declaration

Following is the declaration for java.io.FilterInputStream.available() method −

public int available()

Parameters

NA

Return Value

The method returns an estimate of the number of bytes that can be read.

Exception

IOException − If an I/O error occurs.

Example - Usage of FilterInputStream available() method

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

FilterInputStreamDemo.java

package com.tutorialspoint;

import java.io.BufferedInputStream;
import java.io.FileInputStream;
import java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;

public class FilterInputStreamDemo {
   public static void main(String[] args) throws IOException {
      InputStream is = null; 
      FilterInputStream fis = null; 
      int i = 0, j = 0;
      char c;
      
      try {
         // create input streams
         is = new FileInputStream("test.txt");
         fis = new BufferedInputStream(is);
         
         // read till the end of the file
         while((i = fis.read())!=-1) {
         
            // converts integer to character
            c = (char)i;
            
            // prints
            System.out.print("Read: "+c);
            
            // number of bytes available
            j = fis.available();
            
            // prints
            System.out.println("; Available bytes: "+j);
         }
         
      } catch(Exception e) {
         // if any error occurs
         e.printStackTrace();
      } finally {
         // releases any system resources associated with the stream
         if(is!=null)
            is.close();
         if(fis!=null)
            fis.close();
      }
   }
}

Output(assuming test.txt contains ABCDEF)

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

Read: A; Available bytes: 5
Read: B; Available bytes: 4
Read: C; Available bytes: 3
Read: D; Available bytes: 2
Read: E; Available bytes: 1
Read: F; Available bytes: 0

Example - Using FilterInputStream Directly

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

FilterInputStreamDemo.java

package com.tutorialspoint;

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

public class FilterInputStreamDemo {
   public static void main(String[] args) {
      try {
         // Creating FileInputStream and wrapping it in FilterInputStream
         FileInputStream fileInputStream = new FileInputStream("example.txt");
         FilterInputStream filterInputStream = new FilterInputStream(fileInputStream) {}; // Anonymous subclass

         // Checking available bytes before reading
         System.out.println("Available bytes before reading: " + filterInputStream.available());

         // Reading the first byte
         int data = filterInputStream.read();
         System.out.println("First byte read: " + (char) data);

         // Checking available bytes after reading one byte
         System.out.println("Available bytes after reading: " + filterInputStream.available());

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

Output(assuming example.txt contains Hello World!)

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

Available bytes before reading: 12
First byte read: H
Available bytes after reading: 11

Explanation

• FilterInputStream is instantiated using an anonymous subclass (since it does not provide direct constructors).

• The available() method is called to check the number of bytes before and after reading one byte.

Example - Wrapping FilterInputStream Around FileInputStream

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

FilterInputStreamDemo.java

package com.tutorialspoint;

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

public class FilterInputStreamDemo {
   public static void main(String[] args) {
      try {
         FileInputStream fileInputStream = new FileInputStream("example.txt");

         // Wrapping FileInputStream inside FilterInputStream
         FilterInputStream filterInputStream = new FilterInputStream(fileInputStream) {}; 

         System.out.println("Total available bytes: " + filterInputStream.available());

         // Reading all available bytes into a byte array
         byte[] buffer = new byte[filterInputStream.available()];
         filterInputStream.read(buffer);

         // Printing the file content
         System.out.println("File content: " + new String(buffer));

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

Output(assuming example.txt contains Hello World!)

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

Total available bytes: 12
File content: Hello World!

Explanation

• FilterInputStream is used as a wrapper around FileInputStream.

• The available() method is used to determine how many bytes can be read.

• The file is read completely into a byte array and printed.