Explain when u will use Observer pattern and how u will
implement in c++ .
- 1 Answers
- 3846 Views
- I also Faced
- E-Mail Answers
Answer Posted / subeetha
The observer pattern (a subset of the asynchronous
publish/subscribe pattern) is a software design pattern in
which an object, called the subject, maintains a list of
its dependents, called observers, and notifies observers
automatically of any state changes, usually by calling one
of their methods. It is mainly used to implement
distributed event handling systems.
Sample Program:
#include <iostream>
#include <vector>
using namespace std;
class Subject {
// 1. "independent" functionality
vector < class Observer * > views; // 3. Coupled only
to "interface"
int value;
public:
void attach(Observer *obs) {
views.push_back(obs);
}
void setVal(int val) {
value = val;
notify();
}
int getVal() {
return value;
}
void notify();
};
class Observer {
// 2. "dependent" functionality
Subject *model;
int denom;
public:
Observer(Subject *mod, int div) {
model = mod;
denom = div;
// 4. Observers register themselves with the Subject
model->attach(this);
}
virtual void update() = 0;
protected:
Subject *getSubject() {
return model;
}
int getDivisor() {
return denom;
}
};
void Subject::notify() {
// 5. Publisher broadcasts
for (int i = 0; i < views.size(); i++)
views[i]->update();
}
class DivObserver: public Observer {
public:
DivObserver(Subject *mod, int div): Observer(mod, div){}
void update() {
// 6. "Pull" information of interest
int v = getSubject()->getVal(), d = getDivisor();
cout << v << " div " << d << " is " << v / d
<< '\n';
}
};
class ModObserver: public Observer {
public:
ModObserver(Subject *mod, int div): Observer(mod, div){}
void update() {
int v = getSubject()->getVal(), d = getDivisor();
cout << v << " mod " << d << " is " << v % d
<< '\n';
}
};
int main() {
Subject subj;
DivObserver divObs1(&subj, 4); // 7. Client configures
the number and
DivObserver divObs2(&subj, 3); // type of Observers
ModObserver modObs3(&subj, 3);
subj.setVal(14);
}
14 div 4 is 3
14 div 3 is 4
14 mod 3 is 2
| Is This Answer Correct ? | 3 Yes | 0 No |
Post New Answer View All Answers
Who created stl?
Can we use stl in coding interviews?
What is stl in oop?
How does an stl file work?
Explain stl.
When did c++ add stl?
totoo po ba ang manga aliens!
Q1. A. What is unary operator? List out the different operators involved in the unary operator. B. What is an adjust field format flag? Q2. A. Distinguish between a # include and #define. B. Can a list of string be stored within a two dimensional array? Q3. A.Explain how a pointer to function can be declared in C++? B.List the merits and demerits of declaring a nested class in C++? Q4. A. What are the syntactic rules to be avoid ambiguity in multiple inheritence? B. Explain the operation of overloading of an assignment operator. Q5. A. Explain how the virtual base class is different from the conventional base classes of the opps. B. Explain how an exception handler is defined and invoked in a Program. Q6. A. What is a binary file? List the merits and demerits of the binary file usagein C++. B. Write short notes on Text Manipulation Routines. C. Write bites in Turbo c++ Header (“Include”) Files.
Describe the My Computer and My Documents folders; identify the elements that are present in every Window.
please visit this site you'll find my question this is my homework please answer it if you can http://easyscience.org/ib/lofiversion/index.php/t36168.html
What are the various types of stl containers?
If P is the population on the first day of the year, B is the birth rate, and D is the death rate, the estimated population at the end of the year is given by the formula: The population growth rate is given by the formula: B – D Write a program that prompts the user to enter the starting population, birth and death rates, and n, the number of years. The program should then calculate and print the estimated population after n years. Your program must have at least the following functions: 1. growthRate: This function takes its parameters the birth and death rates, and it returns the population growth rate. 2. estimatedPopulation: This function takes its parameters the current population, population growth rate, and n, the number of years. It returns the estimated population after n years Your program should not accept a negative birth rate, negative death rate, or a population less than 2. please answer my question ....
Describe how to safeguard a system through acquisition of an antivirus Program and systematic backup.
What does stl stand for in basketball?
Is stl open source?
