classes and object-oriented programming time will be more efficientbecause new list containing the students will not be created mortgagesan extended example collapse in housing prices helped trigger severe economic meltdown in the fall of one of the contributing factors was that many homeowners had taken on mortgages that ended up having unexpected consequences in the beginningmortgages were relatively simple beasts one borrowed money from bank and made fixed-size payment each month for the life of the mortgagewhich typically ranged from fifteen to thirty years at the end of that periodthe bank had been paid back the initial loan (the principalplus interestand the homeowner owned the house "free and clear towards the end of the twentieth centurymortgages started getting lot more complicated people could get lower interest rates by paying "pointsat the time they took on the mortgage point is cash payment of of the value of the loan people could take mortgages that were "interest-onlyfor period of time that is to sayfor some number of months at the start of the loan the borrower paid only the accrued interest and none of the principal other loans involved multiple rates typically the initial rate (called "teaser rate"was lowand then it went up over time many of these loans were variable-rate--the rate to be paid after the initial period would vary depending upon some index intended to reflect the cost to the lender of borrowing on the wholesale credit market in principlegiving consumers variety of options is good thing howeverunscrupulous loan purveyors were not always careful to fully explain the possible long-term implications of the various optionsand some borrowers made choices that proved to have dire consequences let' build program that examines the costs of three kinds of loansa fixed-rate mortgage with no pointsa fixed-rate mortgage with pointsand mortgage with an initial teaser rate followed by higher rate for the duration the point of this exercise is to provide some experience in the incremental development of set of related classesnot to make you an expert on mortgages we will structure our code to include mortgage classand subclasses corresponding to each of the three kinds of mortgages listed above in this contextit is worth recalling the etymology of the word mortgage the american heritage dictionary of the english language traces the word back to the old french words for dead (mortand pledge (gage(this derivation also explains why the "tin the middle of mortgage is silent the london interbank offered rate (liboris probably the most commonly used index