class Point { int x; int y; Point(int x, int y) { this.x = x; this.y = y; void movevertically(int y){ this.y += y;

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1 Call b Value (2.1) Aggregation and Comosition EECS200 B: Advanced Object Oriented Programming Fall 2018 CHEN-WEI WANG For illustration, let s assume the following variant of the class: class { int ; int ; (int, int ) { this. = ; this. = ; void moveverticall(int ){ this. += ; void movehorizontall(int ){ this. += ; of Call b Value (1) Consider the general form of a call to some mutator method m1, with contet object s and argument value arg: class Sulier { void m1( T ar) { / maniulate ar / class Client { Sulier s = new Sulier(); T arg =...; s.m1(arg) To eecute s.m1(arg), an imlicit ar := arg is done. A co of value stored in arg is assed for the method call. What can the te T be? [ Primitive or Reference ] T is rimitive te (e.g., int, char, boolean, etc.): Call b Value : Co of arg s value (e.g., 2, j ) is assed. T is reference te (e.g., String,, Person, etc.): Call b Value : Co of arg s stored reference/address is assed. 2 of Call b Value (2.2.1) ublic class Util { void reassignint(int j) { j = j + 1; void reassignref( q) { n = new (, 8); q = n; void changeviaref( q) { q.movehorizontall(); q.moveverticall(); 1 2 ublic void testcallbval() { Util u = new Util(); int i = 10; 5 asserttrue(i == 10); u.reassignint(i); 7 asserttrue(i == 10); 8 Before the mutator call at L, rimitive variable i stores 10. When eecuting the mutator call at L, due to call b value,a co of variable i is made. The assignment i = i + 1 is onl effective on this co, not the original variable i itself. After the mutator call at L, variable i still stores 10. of

2 Call b Value (2.2.2) Call b Value (2..2) Before reassignint During reassignint After reassignint i int 10 i int 10 Before reassignref During reassignref After reassignref i int 10 j int 10 j int 11 q q 8 5 of 7 of Call b Value (2..1) ublic class Util { void reassignint(int j) { j = j + 1; void reassignref( q) { n = new (, 8); q = n; void changeviaref( q) { q.movehorizontall(); q.moveverticall(); 1 2 ublic void testcallbref_1() { Util u = new Util(); = new (, ); 5 refofpbefore = ; u.reassignref(); 7 asserttrue(==refofpbefore); 8 asserttrue(.== &&.==); 9 Before the mutator call at L, reference variable stores the address of some object (whose is and is ). When eecuting the mutator call at L, due to call b value,a co of address stored in is made. The assignment = n is onl effective on this co, not the original variable itself. After the mutator call at L, variable still stores the original address (i.e., same as refofpbefore). of Call b Value (2..1) ublic class Util { void reassignint(int j) { j = j + 1; void reassignref( q) { n = new (, 8); q = n; void changeviaref( q) { q.movehorizontall(); q.moveverticall(); 1 2 ublic void testcallbref_2() { Util u = new Util(); = new (, ); 5 refofpbefore = ; u.changeviaref(); 7 asserttrue(==refofpbefore); 8 asserttrue(.== &&.==8); 9 Before the mutator call at L, reference variable stores the address of some object (whose is and is ). When eecuting the mutator call at L, due to call b value,a co of address stored in is made. [Alias: and q store same address.] Calls to q.movehorizontall and q.moveverticall are effective on both and q. After the mutator call at L, variable still stores the original address (i.e., same as refofpbefore), but its and have been modified via q. 8 of

3 Call b Value (2..2) Shared b Containers (1.1) Before changeviaref During changeviaref After changeviaref 8 q q 9 of Course Facult rof; Course(String title) { this.title = title; void setprof(facult rof) { this.rof = rof; Facult getprof() { return this.rof; 11 of rof 1 Facult String ; Facult(String ) { this. = ; void setname(string ) { this. = ; String getname() { return this.; Aggregation vs. Comosition: Terminolog Container object: an object that contains others. Containee object: an object that is contained within another. e.g., Each course has a facult member as its instructor. Container: Course Containee: Facult. e.g., Each student is registered in a list of courses; Each facult member teaches a list of courses. Container: Student, Facult Containees: Course. e.g., eecs200 taken b jim (student) and taught b tom (facult). Containees ma be shared b different instances of containers. e.g., When EECS200 is finished, jim and jackie still eist! Containees ma eist indeendentl without their containers. e.g., In a file sstem, each director contains a list of. Container: Director Containees:. e.g., Each file has eactl one arent director. A containee ma be owned b onl one container. e.g., Deleting a director also deletes the it contains. Containees ma co-eist with their containers. 10 of Shared b Containers (1.2) ublic void testaggregation1() { Course eecs200 = new Course("Advanced OOP"); Course eecs11 = new Course("Software Design"); Facult rof = new Facult("Jackie"); eecs200.setprof(rof); eecs11.setprof(rof); asserttrue(eecs200.getprof() == eecs11.getprof()); / aliasing / rof.setname("jeff"); asserttrue(eecs200.getprof() == eecs11.getprof()); asserttrue(eecs200.getprof().getname().equals("jeff")); Facult rof2 = new Facult("Jonathan"); eecs11.setprof(rof2); asserttrue(eecs200.getprof()!= eecs11.getprof()); asserttrue(eecs200.getprof().getname().equals("jeff")); asserttrue(eecs11.getprof().getname().equals("jonathan")); 12 of

4 Shared b Containers (2.1) The Dot Notation (.1) In real life, the relationshis among classes are sohisticated. Student cs Course te Facult String id; ArraList<Course> cs; / courses / Student(String id) { this.id = id; cs = new ArraList<>(); void addcourse(course c) { cs.add(c); ArraList<Course> getcs() { return cs; Student String id; ArraList<Course> cs; cs Course te Facult rof; Facult String ; ArraList<Course> te; String ; ArraList<Course> te; / teaching / Facult(String ) { this. = ; te = new ArraList<>(); void addteaching(course c) { te.add(c); ArraList<Course> gette() { return te; 1 of Aggregation links between classes constrain how ou can navigate among these classes. e.g., In the contet of class Student: Writing cs denotes the list of registered courses. Writing cs[i] (where i is a valid inde) navigates to the class Course, which changes the contet to class Course. 15 of Shared b Containers (2.2) ublic void testaggregation2() { Facult = new Facult("Jackie"); Student s = new Student("Jim"); Course eecs200 = new Course("Advanced OOP"); Course eecs11 = new Course("Software Design"); eecs200.setprof(); eecs11.setprof();.addteaching(eecs200);.addteaching(eecs11); s.addcourse(eecs200); s.addcourse(eecs11); asserttrue(eecs200.getprof() == s.getcs().get(0).getprof()); asserttrue(s.getcs().get(0).getprof() == s.getcs().get(1).getprof()); asserttrue(eecs11 == s.getcs().get(1)); asserttrue(s.getcs().get(1) ==.gette().get(1)); 1 of The Dot Notation (.2) String id; ArraList<Course> cs; Facult rof; String ; ArraList<Course> te;... / attributes / / Get the student s id / String getid() { return this.id; / Get the title of the ith course / String getcoursetitle(int i) { return this.cs.get(i).title; / Get the instructor s of the ith course / String getinstructorname(int i) { return this.cs.get(i).rof.; 1 of

5 The Dot Notation (.) String id; ArraList<Course> cs; Facult rof; String ; ArraList<Course> te;... / attributes / / Get the course s title / String gettitle() { return this.title; / Get the instructor s / String getinstructorname() { return this.rof.; / Get title of ith teaching course of the instructor / String getcoursetitleofinstructor(int i) { return this.rof.te.get(i).title; 17 of Owned b Containers (1.1) Director arent 1 Assumtion: s are not shared among directories. class { String ; (String ) { this. = ; 19 of class Director { String ; [] ; int ; / num of / Director(String ) { this. = ; = new [100]; void add(string filename) { [] = new (filename); ++; The Dot Notation (.) String id; ArraList<Course> cs; Facult rof;... / attributes / / Get the instructor s / String getname() { return this.; / Get the title of ith teaching course / String getcoursetitle(int i) { return this.te.get(i).title; 18 of String ; ArraList<Course> te; Owned b Containers (1.2.1) 1 2 ublic void testcomosition() { Director d1 = new Director("D"); d1.add("f1.tt"); 5 d1.add("f2.tt"); d1.add("f.tt"); 7 asserttrue( 8 d1.[0]..equals("f1.tt")); 9 L: 1st object is created and owned eclusivel b d1. No other directories are sharing this object with d1. L5: 2nd object is created and owned eclusivel b d1. No other directories are sharing this object with d1. L: rd object is created and owned eclusivel b d1. No other directories are sharing this object with d1. 20 of

6 Owned b Containers (1.2.2) d1 Right before test method testcomosition terminates: 21 of Director D d d1.[0] d1.[1] d1.[2] 2 f1.tt f2.tt f.tt Owned b Containers (1..1) Version 1: Shallow Co b coing all attributes using =. class Director { Director(Director other) { / value coing for rimitive te / = other.; / address coing for reference te / = other.; = other.; Is a shallow co satisfactor to suort comosition? i.e., Does it still forbid sharing to occur? [ NO ] void testshallowcoconstructor() { Director d1 = new Director("D"); d1.add("f1.tt"); d1.add("f2.tt"); d1.add("f.tt"); Director d2 = new Director(d1); asserttrue(d1. == d2.); / violation of comosition / d2.[0].changename("f11.tt"); assertfalse(d1.[0]..equals("f1.tt")); 2 of Owned b Containers (1.) Problem: Imlement a co constructor for Director. A co constructor is a constructor which initializes attributes from the argument object other. class Director { Director(Director other) { / Initialize attributes via attributes of other. / Hints: The imlementation should be consistent with the effect of coing and asting a director. Searate coies of are created. 22 of Owned b Containers (1..2) d2 d1 Right before test method testshallowcoconstructor terminates: 2 of Director Director d2. D d d1.[0] d1.[1] d1.[2] d2.[0] d2.[1] d2.[2] d2. 2 f11.tt f2.tt f.tt

7 Owned b Containers (1.5.1) Version 2: a Dee Co class { ( other) { this. = new String(other.); class Director { Director(String ) { this. = new String(); = new [100]; Director(Director other) { this (other.); for(int i = 0; i < ; i ++) { src = other.[i]; nf = new (src); this.add(nf); void add( f) {... void testdeecoconstructor() { Director d1 = new Director("D"); d1.add("f1.tt"); d1.add("f2.tt"); d1.add("f.tt"); Director d2 = new Director(d1); asserttrue(d1.!= d2.); / comosition reserved / d2.[0].changename("f11.tt"); asserttrue(d1.[0]..equals("f1.tt")); 25 of Owned b Containers (1.5.) Q: Comosition Violated? class { ( other) { this. = new String(other.); class Director { Director(String ) { this. = new String(); = new [100]; Director(Director other) { this (other.); for(int i = 0; i < ; i ++) { src = other.[i]; this.add(src); void add( f) {... void testdeecoconstructor() { Director d1 = new Director("D"); d1.add("f1.tt"); d1.add("f2.tt"); d1.add("f.tt"); Director d2 = new Director(d1); asserttrue(d1.!= d2.); / comosition reserved / d2.[0].changename("f11.tt"); asserttrue(d1.[0] == d2.[0]); / comosition violated! / 27 of Owned b Containers (1.5.2) Right before test method testdeecoconstructor terminates: d2 d1 Director Director D d2. d2.[0] d2.[1] d2.[2] D d2. d d1.[0] d1.[1] d1.[2] f11.tt f2.tt f.tt Owned b Containers (1.) Eercise: Imlement the accessor in class Director class Director { [] ; int ; [] gets() { / Your Task / so that it reserves comosition, i.e., does not allow references of to be shared. 2 of f1.tt f2.tt f.tt 28 of

8 Aggregation vs. Comosition (1) Terminolog: Container object: an object that contains others. Containee object: an object that is contained within another. Aggregation : Containees (e.g., Course) ma be shared among containers (e.g., Student, Facult). Containees eist indeendentl without their containers. When a container is destroed, its containees still eist. Comosition : Containers (e.g, Director, Deartment) own eclusive access to their containees (e.g.,, Facult). Containees cannot eist without their containers. Destroing a container destros its containeees cascadingl. 29 of Inde (1) Call b Value (1) Call b Value (2.1) Call b Value (2.2.1) Call b Value (2.2.2) Call b Value (2..1) Call b Value (2..2) Call b Value (2..1) Call b Value (2..2) Aggregation vs. Comosition: Terminolog Shared b Containers (1.1) Shared b Containers (1.2) Shared b Containers (2.1) 1 of Aggregation vs. Comosition (2) Aggregations and Comositions ma eist at the same time! e.g., Consider a workstation: Each workstation owns CPU, monitor, keword. [ comositions ] All workstations share the same network. [ aggregations ] 0 of Inde (2) Shared b Containers (2.2) The Dot Notation (.1) The Dot Notation (.2) The Dot Notation (.) The Dot Notation (.) Owned b Containers (1.1) Owned b Containers (1.2.1) Owned b Containers (1.2.2) Owned b Containers (1.) 2 of

9 Inde () Owned b Containers (1..1) Owned b Containers (1..2) Owned b Containers (1.5.1) Owned b Containers (1.5.2) Owned b Containers (1.5.) Owned b Containers (1.) Aggregation vs. Comosition (1) Aggregation vs. Comosition (2) of