Data Types

Programs and CPUs work with values, values are represented in programs by literals and stored in variables 

Literal: “Hello There,” true, -23, etc.

Variables: x, y, helloMessage, etc. (use letters, digits and underscore, start with letter, identifies a location in memory)

Variables/Literals have types

int: Subset of integers, stored in 4 bytes (32 bits), variables declared with “int” are reserved work

Set of OperationsL +, -, *, / and % (mod), remainder 17%3 = 2

Primitive Types: built into language (boolean, byte, short, int, float, float, double, char)

Occupy enough bits to store the value

Reference Types

Can be defined by the user

Hold a “reference” (pointer) to an object

String Type

Set of values: sequences of characters length - to 2,147,483,647

Set of operations: concat() (also + operator), toUpperCase(), length(), substring()

String are immutable, can’t change a string once set

Primitive stores actual value, reference stores address

Variable: memory location where something can be stores, contents of the location can change/vary

Literal: Value cannot be changed, stored in a variable

Declarations

Variables but be declared and given a type

Compiler arranged space to be allocated for the variable to store a value, ensures only valid operations can be performed for given type

Primitive Types

Integer Types in Java

All represent subsets on integers, differs in how many bits used to store the value

Byte: 9 bits (-128 to 127)

Short: 16 bits (-32,768 to 32,767)

int: 32 bits (what’s used in CS 180)

long: 64 bits (18 digits)

Operations on Integer Divide

Mathematical operations

Divide operation is “integer divide,” results in integer regardless of actual solution, called truncation, drops everything after decimal point (13 / 4 is 3)

Real Number Types in Java

Represent subsets of real numbers

Two types, floats (32 bits, single precision) and doubles (64 bits, double precision), 16 bits for exponent, 48 or so for number, double uses bigger/smaller decimals and larger numbers/digits possible so “double precision”

Operations on Real Types

Usual mathematical operations, divide gives actual decimal

Math Class includes other methods (some applicable to integers)

Math.pow(Base, exponent)

Logs, trig, etc.

Declarations

int x; (declare only, 0 by default)

int x = 5; (declare and initialize)

int x, y; (dual declaration)

int x = 5, y = 10; (dual initialization)

Best practice is to declare only one variable per line with comment describing variable

Expressions

Combining variables and literals with operators (+, -, etc)

Usual mathematical precedence, multiplications and division first, addition and subtraction next