main method does is declare and
initialize some variables. Here is the relevant section of code:
double tolerance = .000000001; // Our approximation of zero int max_count = 200; // Maximum number of Newton's method iterations /* x is our current guess. If no command line guess is given, we take 0 as our starting point. */ double x = 0;Java provides an assortment of primitive data types to represent numbers and characters. Here we see two of these types. The first type, which we have seen before in method declarations, is the floating point
double:
double tolerance = .000000001;
This line declares the existence of the variable tolerance and
initializes its initial value to .000000001. This is equivalent to the
two lines:
double tolerance;
tolerance = .000000001;
A variable declaration can occur anywhere in a method and can be used
anywhere "within its scope". By this I mean anywhere after the
declaration and within the set of curly braces that enclose it.
So, if you declare some variables at the beginning of the method, like
we have done in the main method, you can use those variables
everywhere in the method.
We see in our method's variable declarations another data type - the
integer. The variable max_count is of type int,
a 32 bit signed integer, so
it can take on integer values roughly between plus and minus one billion.
We have seen, then, that the main method declares three variables
tolerance of type double which
stores how close to zero we have to come before we declare a root has
been found.
max_count of type int which stores the maximum
number of iterations of Newton's method that we will try before we give up
on finding a root.
x of type double which stores our current guess
of the location of the root.
Since we are talking about primitive variables, I will take this opportunity to mention a couple of other data types that you might find in Java code.
There is a special data type for truth in Java, the boolean.
A variable of type boolean can take on only two values,
true and false.
Another data type that you might see is char. This represents
a single character, so you could make a declaration like this:
char the_letter_a = 'a';
Notice that a character in back-quotes like 'a' is taken to be
of type char.
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5.7.2 Command Line Arguments and Arrays |
David Maxwell,
who is still writing this, would like to
hear your comments and suggestions.