A variable is a memory location in which to store a value.
A variable has a name and a data type.
A variable must be declared before we can assign a value to it.
There are six numerical data types in Java: byte, short, int, long, float, and double.
Object names are synonymous with variables whose contents are memory addresses.
Numerical data types are called primitive data types, and objects are called reference data types.
Precedence rules determine the order of evaluating arithemetic expressions.
Symbolic constants hold values just as variables do, but we cannot change their values.
The standard classes introduced in this chapter are
Math
InputStream
GregorianCalendar
InputStreamReader
DecimalFormat
BufferedReader
PrintStream
IOException
Integer, Double, etc.
We use methods from the wrapper classes Integer, Double, and others to convert an input string to a numerical value.
System.out is used to output multiple lines of text to the standard output window.
System.in is used to input a stream of bytes. We associate a BufferedReader object to System.in (with an intermediate InputStreamReader) to input one line of text at at time.
The Math class contains many class methods for mathematical functions.
The GregorianCalendar class is used in the manipulation of calendar information.
The DecimalFormat class is used to format the numerical data.
(Optional) Twos complement format is used for storing integers, and floating-pointing format is used for storing real numbers.
