Variable Declarations: Primitive Java Data Types

5.7.1 Variable Declarations: Primitive Java Data Types

The first thing that our 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

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.
Next 5.7.2 Command Line Arguments and Arrays

David Maxwell, who is still writing this, would like to hear your comments and suggestions.