BOOK NOTES
CHAPTER 4

4.1 NUMBER TYPES

- every value is either an object reference or a primitive
- p. 105 table of primitive types, usages, and range of values
  - 8 types
  - 6 numeric
    - 4 integer
    - 2 floating point
- generally use int for integers
- overflow: result of computation exceeds range for number type
  - value truncated to fit
  - result is wrong
  - no warning
- long
  - correct int overflow
  - if overflows, use BigInteger
- floating point
  - use double b/c float has low precision
  - rounding error
    - can't always convert exactly
    - binary number system can't represent decimal fractions exactly
    - must use BigDecimal for real financial applications
- casting
  - can assign integers to floating point values
  - cannot assign floating point values to integers
  - explicitly convert between types
  - only required from more precise to less precise
  - synatx: (<typename>) expression
  - tell compiler that agree to information loss
  - (int) <floating point> truncates floating point part
  - use Math.round to round numbers
    - static long round(double x)
    - static int round(float x)

4.2 CONSTANTS

- numerical constants
  - values that do not change
  - have special significance
- use symbolic names for all values
- declare a constant
  - final modifier
  - if try to change, get compile-time error
- naming convention
  - all capital letters
  - use underscores to separate words
- need constant in several methods
  - declare with instance data
  - also declare static
  - declare public because cannot be modified
- examples: double Math.PI, double Math.E
- don't use numeric constants in your code w/out explanation
- choose descriptive variable names: important for sharing code

4.3 ASSIGNMENT, INCREMENT, AND DECREMENT

- increment operator
  - ++
  - increases the value of its operand by one
- decrement operator
  - --
  - decreases the value of its operand by one
- combining assignment and arithmetic
  - a op= b
  - equivalent to a = a op b

4.4 ARITHMETIC OPERATIONS AND MATHEMATICAL FUNCTIONS

- division operator: /
- parenthetical expressions are evaluated first
- multiplication and division bind more strongly than addition and subtraction
- division
  - works as expected if at least one operand is floating point
  - when both operands are integers, the result is a truncated integer
- modulo: remainder of an integer division
- x^n
  - Math class
  - static double pow(double x, doublen)
  - for squares, more efficient to write out
- square root
  - Math class
  - static double sqrt(double x)
- p. 120 Math methods
- whitespace
  - put spaces around all binary operators
  - put a space after every Java keyword

4.5 CALLING STATIC METHODS

- static method 
  - doesn't operate on an object
  - is defined in a class
  - specify with name of class
- naming convention useful in identifying
  - object names always start with a lowercase letter
  - class names always start with a capital letter

4.6 STRINGS

- string: sequence of characters
- enclosing quotation marks
  - used by Java to specify
  - not part of string
- object
- length
  - number of characters in it
  - String int length()
- empty string
  - no characters
  - written ""
- concatenation
  - put strings together to form a longer string
  - + operator
    - provided at least one argument is a string
    - forces other argument to type string
  - reduce number of System.out.print instructions
- convert a string to an int: Integer static int parseInt(String x)
- convert a string to a float: Double static double parseDouble(String x)
- String indices start at 0
- String methods
  - String substring(int startPosition, int pastEnd)
    - returns the String 
    - from index startPosition 
    - up to but not including index pastEnd
  - String substring(int startPosition)
    - including startPosition through the end of the implicit parameter
  - unreasonable parameters cause program to terminate with error message

4.7 READING INPUT

- use System.in object
- use java.util.Scanner class
- pass System.in to the Scanner constructor
- int nextInt() method lets you read the next int
- double nextDouble() method lets you read the next double
- always prompt user before attempting to get input
- input is sent to your program when user hits Enter key
- String nextLine() gets all of the input as a String
- String next() gets the next word (terminated by white 
  space)