Using the Classes let class Vehicle extends Object { . } class Car extend

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Using the Classes let class Vehicle extends Object { . } class Car extend

Arcadia University, US has reference to this Academic Journal, Objects in addition to Classes David Walker CS 320 Advanced Languages advanced programming features ML data types, exceptions, modules, objects, concurrency, . fun so that use, but require special techniques so that compile in addition to optimize today will be looking at how so that compile objects in addition to classes similar so that those found in Java Appel chapter 14.1-14.4 Object Fun Add class declarations so that Fun: classes are a collection of field (variable) declarations method declarations every class declaration gives a new name so that a class a class may inherit methods in addition to fields from the class it extends the class ?object? sits at the top of the class hierarchy; it has no fields in addition to no methods

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An Object Fun Class let class Vehicle extends Object { var position := start method move (x : int) = (position := position + x) } in . end class name superclass that Vehicle inherits from field declaration method declaration Another Object Fun Class let class Vehicle extends Object { var position := start method move (x:int) = (position := position + x) } class Car extends Vehicle { var passengers := 0 method await(v:vehicle) = if (v.position < position) then v.move(position ? v.position) else self.move(10) in . end v?s ?position? field current object?s ?position? field call so that inherited method new field declaration new method declaration Yet Another Object Fun Class let class Vehicle extends Object { var position := start method move (x:int) = position := position + x } class Car extends Vehicle { . } class Truck extends Vehicle { method move (x:int) = if x <= 55 then position := position * x in . end method override Using the Classes let class Vehicle extends Object { . } class Car extends Vehicle { . } class Truck extends Vehicle {.} var t := new Truck var c := new Car var v : Vehicle := c in c.passengers := 2; c.move(60); v.move(70); c.await(t); end new object created subtyping allows a car so that be viewed in addition to used as a generic vehicle subtyping allows a truck so that be viewed in addition to used as a generic vehicle a car calls an inherited method Implementing Object Fun Some key problems: how do we access object fields? both inherited fields in addition to fields in consideration of the current object? how do we access method code? if the current class does not define a particular method, where do we go so that get the inherited method code? how do we handle method override? in both cases, when we generate code, we only know the static type of the object, not the actual dynamic type Class Hierarchy The class hierarchy is the graph of inheritence relationships in a program: In a single-inheritence (SI) language, the graph is a tree In a multiple-inheritence (MI) language, the graph is a dag Multiple-inheritence languages are much trickier so that implement than single-inheritence languages Object Vehicle Car Truck

Speech Recognition Application Process of Speech Recognition Problem Input / Output Difficulties Solution Solution Solution Check List Timeline

Object Layout (SI) Objects are laid out somewhat like records each variable has a slot in the record in order so that implement field lookup we need so that have a systematic way so that find a given field eg: v.position v may be a generic vehicle or it may be a car or a truck we need so that put ?position? in the same place in the record that implements vehicles, cars in addition to trucks Object Layout (SI) Solution: extension on the right lay out the inherited fields first in the same order as in the parent (SI => only 1 parent) lay out the newly declared so that the right Object Layout (SI) class A extends Object { var a := 0 } class B extends A { var b := 0 var c := 0 } class C extends A { var d := 0 } class D extends B { var e := 0 }

Object Layout (SI) class A extends Object { var a := 0 } class B extends A { var b := 0 var c := 0 } class C extends A { var d := 0 } class D extends B { var e := 0 } A a Object Layout (SI) class A extends Object { var a := 0 } class B extends A { var b := 0 var c := 0 } class C extends A { var d := 0 } class D extends B { var e := 0 } B a b c A a Object Layout (SI) class A extends Object { var a := 0 } class B extends A { var b := 0 var c := 0 } class C extends A { var d := 0 } class D extends B { var e := 0 } C a d B a b c A a

Object Layout (SI) class A extends Object { var a := 0 } class B extends A { var b := 0 var c := 0 } class C extends A { var d := 0 } class D extends B { var e := 0 } D a b c e C a d B a b c A a Static & Dynamic Methods The result of compiling a method is some machine code located at a particular address at a method invocation point, we need so that figure out what code location so that jump so that Java has static & dynamic methods so that resolve static method calls, we look at the static type of the calling object so that resolve dynamic method calls, we need the dynamic type of the calling object Static Methods during semantic analysis, the compiler knows: static type (class) of the object calling the method the list of methods in each class in addition to determines the closest method (up the class hierarchy) alongside the given name in addition to inserts instructions so that pass object as self parameter a direct call so that the known method let class A extends Object { static method foo (x:int) = . static method bar (x:int) = . } class B extends A { static method foo (x:int) = . } var a : A = new A var b : A = new B var c : B = new B in a.foo(3); (* calls foo in class A *) b.foo(3); (* calls foo in class A *) c.bar(3); (* calls bar in class A *) c.foo(3); (* calls foo in class B *)

Dynamic Methods Method called depends on object?s dynamic type During semantic analysis, may be unknown At run-time, we determine which code so that jump so that object stores a pointer so that its method table (v-table) as well as its object vars At compile-time, we generate code so that look up v-table in object extract method from table jump so that method body let class A extends Object { method foo (x:int) = . method bar (x:int) = . } class B extends A { method foo (x:int) = . } var a : A = new A var b : A = new B var c : A = if long-and-tricky-computation then a else b in c.foo(3) Object Layout II (SI) class A extends Object { var a := 0; method f () } class B extends A { method g () } class C extends B { method g () } class D extends C { var b := 0 ; method f () } Object Layout II (SI) class A extends Object { var a := 0; method f () } class B extends A { method g () } class C extends B { method g () } class D extends C { var b := 0 ; method f () } A a A_f

Object Layout II (SI) class A extends Object { var a := 0; method f () } class B extends A { method g () } class C extends B { method g () } class D extends C { var b := 0 ; method f () } B a A a A_f A_f B_g Object Layout II (SI) class A extends Object { var a := 0; method f () } class B extends A { method g () } class C extends B { method g () } class D extends C { var b := 0 ; method f () } C a B a A a A_f A_f B_g A_f C_g Object Layout II (SI) class A extends Object { var a := 0; method f () } class B extends A { method g () } class C extends B { method g () } class D extends C { var b := 0 ; method f () } D a b C a B a A a A_f A_f B_g A_f C_g D_f C_g

Object Layout II (SI) class A extends Object { var a := 0; method f () } class B extends A { method g () } class C extends B { method g () } class D extends C { var b := 0 ; method f () } D a b C a B a A a A_f A_f B_g A_f C_g D_f C_g D a b Multiple Inheritence Multiple inheritence is trickier so that implement than single inheritence because creating objects of a subclass from their subclass by ?extension on the right? doesn?t work if C inherits from both A in addition to B, we can?t put A?s variables at the front in addition to put B?s variables at the front of the object in the same place! we need so that do a global analysis so that determine object layout Object Layout (MI) class A extends Object { var a := 0 } class B extends Object { var b := 0 var c := 0 } class C extends A { var d := 0 } class D extends A,B,C { var e := 0 } D a b c e C a d B b c A a d

Object Layout (MI) class A extends Object { var a := 0 } class B extends Object { var b := 0 var c := 0 } class C extends A { var d := 0 } class D extends A,B,C { var e := 0 } D a b c e C a d B b c A a d Determine object layout by: global graph coloring! a node in consideration of each field name an interference edge between names that coexist in the same class (via inheritence or otherwise) Object Layout (MI) class A extends Object { var a := 0 } class B extends Object { var b := 0 var c := 0 } class C extends A { var d := 0 } class D extends A,B,C { var e := 0 } D a b c e C a d B b c A a d wasted space in every object Object Layout II (MI) class A extends Object { var a := 0 } class B extends Object { var b := 0 var c := 0 } class C extends A { var d := 0 } class D extends A,B,C { var e := 0 } D a b c e C a d B b c A a d 1 1 2 1 2 1 2 3 5 4 wasted space per class a: a: b: a: d: a: b: c: d: e:

Other OO Features Protection mechanisms so that encapsulate local state within an object, Java has ?private? ?protected? in addition to ?public? qualifiers private methods/fields can?t be called/used outside of the class in which they are defined during semantic analysis (type checking), the compiler maintains this information in the symbol table in consideration of each class Summary Object-oriented languages provide new challenges in consideration of compiler writers how so that find fields in addition to methods how so that make field in addition to method access just as efficient as ordinary function call in addition to variable lookup lots of ongoing research in OO language implementation tackles these in addition to other interesting questions

Allemao, Andy General Assignment Business Reporter

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Journal Ratings by Arcadia University

This Particular Journal got reviewed and rated by Object Layout II (SI) class A extends Object { var a := 0; method f () } class B extends A { method g () } class C extends B { method g () } class D extends C { var b := 0 ; method f () } D a b C a B a A a A_f A_f B_g A_f C_g D_f C_g D a b Multiple Inheritence Multiple inheritence is trickier so that implement than single inheritence because creating objects of a subclass from their subclass by ?extension on the right? doesn?t work if C inherits from both A in addition to B, we can?t put A?s variables at the front in addition to put B?s variables at the front of the object in the same place! we need so that do a global analysis so that determine object layout Object Layout (MI) class A extends Object { var a := 0 } class B extends Object { var b := 0 var c := 0 } class C extends A { var d := 0 } class D extends A,B,C { var e := 0 } D a b c e C a d B b c A a d and short form of this particular Institution is US and gave this Journal an Excellent Rating.