CPSC 2150 - DAY 9
SEPTEMBER 20, 2016

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Interface Specification 

Stack 
	-Last in first out structure

Interfaces reduce confusion among a team of developers

Dual Ideas of Specification

	.Information hiding - hide details unnecessary to use the interface
	.Abstraction - provide explanation or cover story

Users should not have to depend on implementation details

Strings
-------

can be thought of as a series of zero or more entries of any other mathematical
type, say T.

	We will call this Str(T)
	Also denoted in computing foundations as T*

String is a programming type in Java, str(T) is a mathematical structure, like
a set

Unlike sets, there may be duplicate entries(in fact there may be as many as you
want)

The empty string, a string with no entries < > or empty_string

Concatenation of strings s and t,

<1,2> o <3, 2> = <1, 2, 3, 2>
< > o <5, 2, 13> = <5, 2, 13>
< > o < > = < >

the length of a string is denoted by |s|

#this - value before

pop from strings from the left