VARIABLES
- variable: named memory location (name w/ any valid identifier)
- to use, must first declare: associate a name with a type, and allocate memory for it
- to know how to allocate memory upon declaration, must provide data type
  - integers: byte, short, int, long
  - real numbers: float, double
  - vary in precision:
    - range of values represented
    - amount of memory required (only significant if declaring thousands of variables -- not in this course)
- declaration syntax: <data type> <variable name>;
  - once declared, cannot change type
  - must declare a variable before use
  - cannot declare same variable more than once
  - no lim on num dif declarations
- assignment statement: store a value in a variable
  - syntax: <variable> = <expression>;
  - don't confuse w/ mathematical equality
- initialization: giving a variable its first value
  - good practice to always do
  - can do upon declaration: <data type> <variable name> = <initial value>;

ARITHMETIC EXPRESSIONS
- arithmetic operator: designates numerical computation
- operand
  - what the operator operates on
  - constant, variable, method call, arithmetic expression
- binary operator: operates on 2 operands
- unary operator: operates on 1 operand
  - e.g. negation "-"
- arithmetic expression
  - expression involving numerical values
  - consists of arithmetic operators and operands
- division
  - both operands are ints
    - fractional part is truncated
    - "integer division"
  - one operand is real; result is real
- modulo
  - remainder of division
  - can use on reals
  - typically only used on ints
- subexpression: nested expression
- precedence rules
  - determine order of evaluation
  - two or more operators
- if operands of same type, result will have that type, too
- type casting: convert one data type to another
  - implicit
    - numeric promotion
      - applied to operands of arithmetic expr
      - operand converted from lower to high precision
    - assignment conversion
      - occurs when var & val in assignment statement have mismatching types
      - only if var has higher precision
  - explicit
    - type cast operator
      - syntax: (<data type>) <expression>
      - unary operator
      - precedence > binary 

SAMPLE JAVA STANDARD CLASSES: STRING
- represent textual values
- sequence of characters surrounded by quotes
- methods
  - concatenation
    - create a new string from two existing ones
    - <first string> + <second string>
    - cannot concatenate null

CONSTANTS
- values of variables may vary with time
- constant: lock assigned value assigned to identifier
  - declaration: final <type> <NAME> = value;
  - Java naming convention: only capital letters and underscores
  - judicious use increases readability
- named constant: referred to w/ identifier
- literal constant: referred to w/ actual value
- default type of integer literal constants is int
  - specify long by appending l or L
- default type of real literal constants is double
  - specify float by appending f or F
  - specify double by appending d or D
- exponential notation
  - represents scientific notation
  - syntax: <number> E <exponent>
  - <number>
    - literal const
    - may contain decimal point
  - can use e instead of E
  - <exponent> is signed or unsigned int
  - may suffix entire expression w/ float or double modifiers

GETTING NUMERICAL INPUT VALUES
- type mismatch:  error caused by assigning a given type to a different, incompatible one
  - different representations in memory
- wrapper class: utility that surrounds primitive data with useful methods
- Integer class
  - parseInt method
    - convert Strings to ints
    - if can't convert, causes error
- concatenation
  - + for strings
  - also for strings and numerical
    - automatically converts numbers to strings, then concatenates
- operator overloading
  - symbol used to represent > 1 operation
  - compiler determines meaning by context
    - treat as addition if both operations numerical (else concatenates)
    - evaluated left to right
    - result of concatenation is text
- DecimalFormat class
  - specify number of decimal places to display
  - package java.text

STANDARD OUTPUT
- standard output window
  - window w/ black background
  - appearance varies w/ dev tool used
  - always functions the same
- System class
  - useful class data values
    - instance of PrintStream class named out
    - PrintStream object tied to standard output window
- System.out
  - text sent to appears in standard output window
  - use to output multiple lines of text
  - use to output numerical values via conversion to text
- standard output: technique of displaying data via System.out
- print method
  - output a value
  - continue printing from end of currently displayed output
  - implicitly does type conversion to display numerical values as parameters (for any primitive)
- println method
  - print an argument and skip to next line
  - typical to use once for each line of output

SAMPLE JAVA STANDARD CLASSES, CONT'D
STRING, CONT'D
- explicit use of new optional
- methods
  - substring

VARIABLES CONT'D
- reference (object) and primitive (e.g. numerical) data types
  - primitive actually contains the data; object contains address of object data
  - declaring primitive creates room to store primitive; declaring reference creates room to store reference
  - to actually make the object referred to, must use new
  - actual variable is always same size in memory, but object (even of same class) can require varing amts of mem
- assigning one obj var to another
  - does not create new object
  - two names for the same object