Java

Java

1. Encoding Sets

   • ASCII
     • Stands for American Standard Code for Information Exchange. Represents 128 alphanumeric characters with each character taking up 7 bits.
     • extended ASCII
       • An extended ASCII set which includes additional German characters and the British Pound symbol. Each character is represented with 8 bits.
   • Unicode
     • UTF-8
       • A encoding which transforms Unicode characters into variable byte lengths. ASCII characters are 8 bits and more complex characters have their length varied. Very commonly used in internet applications
     • UTF-16
       • An encoding which places all most commonly used characters in 16-bit units and places less often used characters into 16-bit pairs.
     • UTF-32
       • Encoding which uses 32 bits for every single character. Not very useful for internet applications
     • Character set created by the Unicode Consortium. Attempts to include all characters in all worldwide languages into a single character set. Currently supported in Java.
   • ISO-8859-1
     • Stands for International Standards Organization, contains all characters required for most western European languages. Each character takes up 8-bits

2. Primitives

   • Data types that are not objects. Specify data format and size of variables
   • Numerical
     • byte
       • Integer which takes up 8 bits. -128 to 127
     • short
       • Short integer - 16 bits, -32768 to 32767
     • int
       • Integer - 32 bits, -2^31 to 2^31-1
     • long
       • Long integer - 64 bits, -2^63 to 2^63-1
     • float
       • Single-precision floating point - 32 bit, 14e^-45 to 3.4028234e^38
     • double
       • Double-precision floating point - 64 bit, 4.9e^-324 to ~= 2e^308
   • Non-numerical
     • char
       • Contains a single Unicode character
     • boolean
       • A true or false value with two states

3. Variables

   • Data placeholder; all variables must have a declared type and an identifier
   • Types
     • Reference
       • Reference type variables refer to an object
     • Primitive
       • Primitive type variables hold a primitive
   • Identifiers
     • An unlimited length of Java letters and Java digits which identify a variable. Cannot be a Java keyword or start with a Java number
     • Java Letter
       • Includes upper and lowercase ASCII Latin letters A to Z, the ASCII underscore "_", and the dollar sign "$"
     • Java Digit
       • Includes ASCII digits 0-9
     • The Ideal variable name starts with a lowercase letter then each subsequent word starts with a capital letter. i.e. userName

4. Constants

   • Variables whose values cannot be changed. A constant can be declared with the keyword final.

5. Literals

   • Source code representation of a value
   • Integer
     • Base 10
       • Standard number system; Base 10 is expressed as a standard number
     • Hexadecimal
       • Number system with base 16; expressed in Java with prefix 0X, i.e. 0X9E
     • Octal
       • Number system with base 8; expressed in Java with prefix 0, i.e. 0567
     • Types
       • byte, short, int
         • Number is written normally; Number must not exceed variable capacity
       • long
         • Number must end with "L" or "l"
   • Floating-Point
     • Float literal
       • Number with 5 parts: Whole number part, decimal point, fractional part, optional exponent, "F" or "f". i.e. 3.14e2F
     • Double literal
       • Number with 5 parts: Whole number part, decimal point, fractional part, optional exponent, "D" or "d". i.e. 5.26e89D
   • Boolean
     • Can be two values: true, false
   • Character
     • Unicode character or escape sequence in single quotes.