Summary of Class Presentation for June 10, 1999

	Java has eight primitive data types, namely:
Integers:
	Byte  -128 to 127
	Short  16 bits
	Int	32 bits
	Long	64 bits
Floats:
	Float	32 bits
	Double	64 bits
Others:
	Boolean	true, false
	Char	16 bits Unicode

Among the integers, a shorter type variable or constant may be assigned 
to a longer type variable and conversion will be done automatically.
Assignment of a longer type variable or constant may be done to a 
shorter type variable only by using an explicit cast.  

	Unlike C or C++, there are no unsigned integers.  The lengths and
ranges of the types are defined by the language and cannot vary from 
implementation to implementation.

Among the floats, conversion from floats to doubles is automatic.  
Using a double for assignment to a float is possible, but only with an 
explicit cast.  Since the cast does no actual conversion,
the result usually is not what you expect.  Only the truncated bits are
used.

	Other conversions among these eight primitive types are not 
allowed.

	Everything else in Java software is an object or a class.

	When parameters are passed in Java, they are always passed by
value.  This means a copy of the value is made and that is passed.
However, every object is actually a reference to a piece of memory 
containing the instance variable values and a table providing access to
the member methods plus a reference to the containing class ( the one 
the object's class inherits from).  Thus when an object is passed, the
reference is copied and used.  This means the original object's data can
be changed in the called method by changing the parameter's data fields.

	The same gotcha occurs on assignments.  If there are two objects,
a and b, an assignment of a to b results in a and b having the same 
reference value and hence each being an alias for the same data fields.

	This gotcha also occurs on relational tests.  For example if a
and b are objects, a == b is only true if a and b contain the same 
reference value.  There is a method that compares the data values 
referenced by the two objects and we will describe this method ( equal)
in a later class.

	We also looked at the operators available in Java.  Nearly all 
are the same as those in C++.