PushbackInputStream PushbackInputStream(InputStream, int) in Java

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

Syntax:

java.io.PushbackInputStream.PushbackInputStream(InputStream in, int size)

This method takes two arguments. This method creates a PushbackInputStream with a pushback buffer of the specified size, and saves its argument, the input stream, for later use.

Note: Initially, the pushback buffer is empty.

Parameters: Two parameters are required for this method.

in: the input stream from which bytes will be read.

size: the size of the push back buffer.

Throws:

1. IllegalArgumentException - if size <= 0.

Approach 1: When no exception

Java

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

public class PushbackInputStreamPushbackInputStream2 {
    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);
        pushbackInputStream.close();
    }
}

Output:

java.io.PushbackInputStream@4361bd48

Approach 2: IllegalArgumentException

Java

package com.PushbackInputStream;

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

public class PushbackInputStreamPushbackInputStream2 {
    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);
        pushbackInputStream.close();
    }
}

Output:

Exception in thread "main" java.lang.IllegalArgumentException: size <= 0
	at java.base/java.io.PushbackInputStream.<init>(PushbackInputStream.java:92)
	at com.PushbackInputStream.PushbackInputStreamPushbackInputStream2.main(PushbackInputStreamPushbackInputStream2.java:18)

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.