PushbackInputStream available() in Java

available(): This method is available in the java.io.PushbackInputStream class of Java.

Syntax:

int java.io.PushbackInputStream.available() throws IOException

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

Note: The method returns the sum of the number of bytes that have been pushed back and the value returned by available.

Parameters: NA

Returns: the number of bytes that can be read (or skipped over) from the input stream without blocking.

Throws:

1. IOException - if this input stream has been closed by invoking its close() method, or an I/O error occurs.

Approach 1: When no exception

Java

import java.io.IOException;
import java.io.InputStream;
import java.io.PushbackInputStream;

public class PushbackInputStreamavailable {
    public static void main(String[] args) throws IOException {

        InputStream in = new InputStream() {

            @Override
            public int read() throws IOException {
                return 10;
            }
        };
        int size = 10;
        PushbackInputStream pushbackInputStream = 
                          new PushbackInputStream(in, size);

        System.out.println(pushbackInputStream.available());
        pushbackInputStream.close();
    }
}

Output:

0

Approach 2: IOException 

Java

package com.PushbackInputStream;

import java.io.IOException;
import java.io.InputStream;
import java.io.PushbackInputStream;

public class PushbackInputStreamavailable {
    public static void main(String[] args) throws IOException {

        InputStream in = new InputStream() {

            @Override
            public int read() throws IOException {
                return 10;
            }
        };
        int size = 10;
        PushbackInputStream pushbackInputStream = 
                      new PushbackInputStream(in, size);

        pushbackInputStream.close();
        System.out.println(pushbackInputStream.available());

    }
}

Output:

Exception in thread "main" java.io.IOException: Stream closed
	at java.base/java.io.PushbackInputStream.ensureOpen(PushbackInputStream.java:74)
	at java.base/java.io.PushbackInputStream.available(PushbackInputStream.java:273)
	at com.PushbackInputStream.PushbackInputStreamavailable.main(PushbackInputStreamavailable.java:21)

Some other methods of PushbackInputStream

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

mark(int): This method marks the current position in this input stream.

markSupported(): This method tests if this input stream supports the mark and reset methods, which it does not.

PushbackInputStream(InputStream): This method creates a PushbackInputStream with a 1-byte pushback buffer and saves its argument, the input stream, for later use.

PushbackInputStream(InputStream, int): This method creates a PushbackInputStream with a pushback buffer of the specified size, and saves its argument, the input stream, for later use.

read(): This method reads the next byte of data from this input stream.

read(byte[], int, int): This method reads up to len bytes of data from this input stream into an array of bytes.

reset(): This method repositions this stream to the position at the time the mark method was last called on this input stream.

skip(long): This method skips over and discards n bytes of data from this input stream.

unread(byte[]): This method pushes back an array of bytes by copying it to the front of the pushback buffer.

unread(int): This method pushes back a byte by copying it to the front of the push-back buffer.

unread(byte[], int, int): This method pushes back a portion of an array of bytes by copying it to the front of the pushback buffer.