Pages 25-39

Pages 25-39

1. character encoding increases efficiency of storing and transmitting unicode text

   • character encoding = data compression
   • Unicode Consortium endorses three types of character encoding systems
     • UTF-8
       • used when unicode is transformed to variable lengths of bytes
     • UTF-16
       • all commonly used characters fit into a single 16-bit code unit
     • UTF-32
       • uses 32 bits for every single character. Much data, not used for internet applications
   • Unicode

2. Java uses ASC2 for almost all input elements except comments, identifiers, and the insides of strings/characters

3. Separators

   • (); {}; []; <>; ; ;:,;.

4. Primitives

   • byte; short; int; long; float; double; char; boolean
   • bytes contains a whole number b/t -128 and 127
     • a byte is 8 bits so 256 possible values.
   • An int can store up to # 1000000
   • Use different values for storage purposes. byte uses the least amount of memor. int uses more and long even more

5. Variables

   • variables are data placeholders
     • 2 types: reference types and primitive types
       • reference types points toward an object
       • primitive types hold a primitive
   • identifiers are an unlimited length sequence of java letters/numbers
     • must begin with a Java letter. Must not be a Java keyword/boolean/or null literal. It must be unique

6. Java Letters and Digits

   • Include uppercase and lowercase ASCII Latin letters
   • Declare a variable by writing the type first then the name plus a semicolon
   • Can declare multiple variables on same line: int a, b;
   • Variable names should be short and meaningful. Lowercase first then Uppercase: dogCat

7. Constants

   • use final to assign a value to a variable which you don't want changed

8. Literals

   • literal = source code representation of a value
     • 3 types: primitive types, string literals, null literal
       • 4 types of primitive literals: integer literals, floating point literals, character literals, boolean literals
         • Integer Literals
           • decimal = base 10; hexadecimal = base 16; octal = base 8
           • used to assign values to bytes, short, int, and long
             • When assigning a value to long be sure to use L after the number: long a = 0900L. otherwise it registers as an int
         • Floating-Point Literals
           • Floating-Point: a whole number part. a decimal point. A fractional part. An optional exponent
             • Float or Double. Float = 32 bits. Double = 64 bits
         • Boolean Literals
           • Two literals = true and false
         • Character Literal
           • enclosed in single quotes
           • escape characters: "\n"

9. Primitive Conversions

   • identity conversion: conversion from a type to the same type
     • Always succesful
   • Widening conversion and narrowing conversion: conversion from a type to another type
     • Not always sucessful
     • Widening Conversion
       • converts from small type to an equal size type or a larger type: int to long
         • No information loss
     • Narrowing Conversion
       • converts from a large type to a smaller type: long to int
         • need to specify the target type in parentheses: long a = 10; int b = (int) a;
         • may incur information loss

10. Operators

    • performs an operation on 1, 2 or 3 operands: x + 4. The + is the operator
    • Operators that require only 1 operand are unary operator
      • binary = 2 operands
    • six categories: unary operators, arithmetic operators, relational and conditional operators, shift and logical operators, assignment operators, and other operators