CSC297 2003F (TAO of Java), Class 3: Basic Types

Admin:
* Any questions yet?
  * We'll talk about BishopD's stuff at the end of class.
* I'm behind on writing for you.  You'll get some stuff soon.
* Handout: <i>C++ Plus Data Structures</i>
* Don't forget to keep the API at hand.

Overview:
* Declaring variables
* Built-in Types
* Primitive Types
* Non-primitive built-in types

Declaring Variables:
* All variables must be declared in Java.
* TYPE VARIABLE_NAME ;
  * String name;
  * int grade;
* TYPE VARIABLE_NAME = INITIALIZIATION ;
  * String name = "Hero Man";
  * int grade = -5;
* Why require programmers to type and declare variables?
  * Helps avoid "spelling error" problems.
  * When a programmer uses a variable in a way incompatible with its type, he or she is usually mistaken.

Built-In Types
* Every object-oriented language needs built-in types
* Language design decision: Are built-in types objects or "something else"?
* In Java, there are "primitive" types that are not objects.  (Essentially, they provide an interpretation of the underlying bits.)
  * boolean: truth values (true, false) (nothing else)
  * char: basic characters ('a', 'some-chinese-character'), uses Unicode
  * int: integer with restricted range (approximately -2^31 to 2^31)
  * short: integer with smaller restricted range (approximately -2^16 to 2^16)
  * long: integer with bigger restricted range (approximately -2^64 to 2^64)
  * float: approximated real number
  * double: better approximated real number
* Why three versions of integer?
  * Memory usage: bigger range numbers require more memory
* All of these built-in types have a syntax for direct entry of values
  * true, false: boolean
  * 'a': character
  * 12312: int or variant
  * 12.4: double
  * 12.4f: float
* There are lots of built-in operations for these values
  * addition: +
  * subtraction: -
  * multiplication: *
  * division: /
  * modulus: %
* What happens when you give one of these operations "incompatible" arguments (e.g., 3 + 4.5)?
  * Converts "less general" to the "more general" type.
* Every primitive type has a corresponding class that provides some useful functionality and information
  * E.g., java.lang.Integer
* How do you input (from the keyboard or file) a value of one of the primitive types?
  * Read a string
  * "Parse" it to get the underlying number.
* Some built-in types are actually classes
  * String is the most common example
  * String student = "Alex";