类属是一种(47)机制，类届类可以看成是类的(48)。

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Structured　programming　practices(71)rise　to　Pascal,　in　which　constructs　were　introduced　to　make　programs　more　readable　and　better(72)C　provided　a　combination　of　assembly　and　high　-level　　structure　to　create　a　general　-purpose　language　that　could　be　used　from　system　to(73)programming.　　Next　came　object　orientation,　which　is(74)of　a　metrology　and　design　philosophy　than　a　language　　issue.　This　is(75)by　the　addition　of　so　-　called　OO　extensions　to　current　language,　such　as　C++.

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Application　development　increasingly　means　Windows　development,　and　the　popularity　of　visual　development　tools　has(66)in　tandem　with　Windows　itself.　These　tools　create　beautiful　windows　wing(67)and　their　fast　development　cycles　and　easy　learning　curves　make　them　a　good(68)for　many　types　of　PC　development　projects.　Today's　developers　are　leveraging　these　tools　and　the　abundance　of　cheap,　powerful　PCs　to　shift　the　balance　of　power　to　the　desktop.　As　the　world　moves　inexorable　toward　Window　and　other(69).　user　interfaces,　developers　can　choose　from　an　abundance　of(70)oriented　tools.　Popular　examples　include　Microsoft　Corp's　Visual　Basic,　powersoft　Corp's　PowerBuilder,　Gupta　Technology　Corp's　SQL　Windows,　and　so　on.