A DESCRIPTION OF THE PROBLEM :
It looks like java.io.PushbackInputStream was designed in JDK 1.0 to only pushback a single byte, was expanded in JDK 1.1 to allow any number of bytes, but the documentation wasn't fully updated.

(1) The first sentence of the class doc says:

>A PushbackInputStream adds functionality to another input stream, namely the ability to "push back" or "unread" one byte.

However, a PushbackInputStream now has a user-specified buffer capacity. It is not limited it one byte. Fixed version:

>A PushbackInputStream adds functionality to another input stream, namely the ability to "push back" or "unread" bytes, by storing pushed-back bytes in an internal buffer.

(2) Both constructors contain the following sentence:

>Initially, there is no pushed-back byte (the field pushBack is initialized to -1).

However, there is no such field. Fixed version:

>Initially, the pushback buffer is empty.

(3) The one-arg constructor neglects to mention the size of the pushback buffer it creates. It should say:

>Creates a PushbackInputStream with a 1-byte pushback buffer ...


URL OF FAULTY DOCUMENTATION :
https://docs.oracle.com/javase/8/docs/api/java/io/PushbackInputStream.html