Standard Input Exception

Answer:
System.in is an InputStream, and like any InputStream, an I/O error may occur when you read from it. For example, the Java program may have been run as a background process with no standard input, causing an error during a read attempt.

InputStream.read() throws an IOException if an error occurs while reading from the stream. This exception is not derived from RuntimeException and must be caught or else your program will not compile.