<p>I have heard mixed opinions over the amount of memory that a byte takes up in a java program.</p>

<p>I am aware you can store no more than +127 in a java byte, and the <a href="http://java.sun.com/docs/books/tutorial/java/nutsandbolts/datatypes.html" rel="noreferrer">documentation</a> says that a byte is only 8 bits but <a href="http://www.jguru.com/faq/view.jsp?EID=13647" rel="noreferrer">here</a> I am told that it actually takes up the same amount of memory as an int, and therefore is just a Type that helps in code comprehension and not efficiency. </p>

<p>Can anyone clear this up, and would this be an implementation specific issue?</p>

Java is never implementation or platform specific (at least as far as
primitive type sizes
are concerned).  They primitive types are always guaranteed to stay the same no matter what platform you're on.  This differs from (and was considered an improvement on) C and C++, where some of the primitive types were platform specific.
Since it's faster for the underlying operating system to address four (or eight, in a 64-bit system) bytes at a time, the JVM may allocate more bytes to store a primitive byte, but you can still only store values from -128 to 127 in it.