Language Fundamentals

Language Fundamentals

1. ASCII & Unicode

   • ASCII (American Standard Code for the Information Exchange)
     • character set to rep alphanumeric characters
     • Each rep. By 7 bits // 128 characters in this character set
     • “extended ASCII” = later expanded to include another 128 characters
       • Each represented by 8 bits
     • Java uses ASCII or almost all input elements (except comments/identifiers/contents of characters and strings )
   • Unicode
     • Attempts to include all characters in all languages into one singular character set
     • INITIALLY represented by 16 bit - used to rep more than 65k characters
     • HOWEVER, wanted possibility of a million more 32 bit system is considered a convenient way of storing Unicode characters // Makes it less efficient
       • character encoding can make unicode more efficient
         • 3 main types
           • UTF-8
             • Pop for HTML and protocols whereby transformed into a variable length encoding of bytes
             • Advantage: that Unicode characters corresponding to the ASCII set have the same byte values as ASCII
           • UTF-16
             • More commonly used characters fit into single 16 bit code unit
             • Less used characters accessible via pairs of 16 bit code unit
           • UTF-32
             • not available for internet use at the moment
             • uses 32 bit for every character

2. Separators

   • parentheses: ( )
     • used in
       • 1. method signatures to contsain a list of args
       • 2. expressions to raise operator precedence
       • 3. narrowing conversation
       • 4. loops to contain expressions to be eval
   • braces: { }
     • used in
       • 1. declaration of types
       • 2. blocks of statements
       • 3. array initialization
   • brackets: [ ]
     • used in
       • 1. array declaration
       • 2. array value deferencing
   • angle brackets: < >
     • used to pass parameter to parameterized types
   • semicolon: ';'
     • 1. used to terminate statements
     • 2. used inn the FOR statement to separate the initialization code, the expression, and the update code
   • colon: ':'
     • used in the FOR statement that iterates over an array or a collection
   • comma: ','
     • used to separate arguments inn method declarations
   • period: '.'
     • used to separate package names from sub-packages and type names, and to separate a field or method from a reference variable

3. Primitives

   • different data type than 'object'
   • 8 different types in java w/specific size & format
     • byte
       • 8 bit
     • short
       • " short int " - 16 bit
     • int
       • 32 bit
     • long
       • " long int " - 64 bit
     • float
       • single precision floating point (32 bit)
     • double
       • double precision floating point (64 bit)
     • char
       • single unicode character
       • doesn't have to be a character in english alphabet
     • boolean
       • boolean value
       • true OR false

4. Variables

   • data placeholder
   • every variable needs DECLARED TYPE
     • reference type
       • reference to object
     • primitive type
       • holds a primitive
   • needs an IDENTIFIER
     • Unlimited-length sequence of java letters and digits
     • must not be a java keyword, a boolean literal, or null literal
     • Must be unique within its scope
   • How Java stores integer values:
     • Byte takes 8 bit - meaning 8 bits allocated to store a byte
     • Leftmost but is the sign bit 0 = + & 1 = -
   • How to declare variables
     • write the type , followed by name + a semi colon

5. Constants

   • variables whose values, once assigned, can't be changed
   • ex: "final int ROW_COUNT = 50;"
   • declared w/ 'final'
   • all uppercase w/ words separated by underscores

6. Literals

   • Occasionally will need to assign values to variables in program (such as #2 to an int or ‘c’ to char)
   • 3 types of literals
     • string literals
     • primitive types
       • 4 subtypes
         • Integer literals
           • Used to assign values to variables of types: byte, short, int, long
         • floating -point literals
           • Floating point numbers include: A whole number part, a decimal point, a fractional part, an optional exponent
         • Character literals
           • Unicode character or an escape sequence enclosed in single quotes
         • Boolean literals
           • true or false
     • null literals