设计模式
https://www.runoob.com/design-pattern/design-pattern-intro.html
委托模式
class I /*interface*/ {
public:
virtual void f() = 0;
virtual void g() = 0;
};
class A : public I {
public:
void f(){std::cout << "A::f()" << std::endl;}
void g(){std::cout << "A::g()" << std::endl;}
};
class B : public I {
public:
void f(){std::cout << "B::f()" << std::endl;}
void g(){std::cout << "B::g()" << std::endl;}
};
class C : public I {
public:
C() { m_i = new A();/*delegation*/ }
void f(){ m_i->f(); }
void g(){ m_i->g(); }
// normal attributes
void toA(){ m_i = new A(); }
void toB(){ m_i = new B(); }
private:
I* m_i;
}
工厂模式
public class ShapeFactory {
//使用 getShape 方法获取形状类型的对象
public Shape getShape(String shapeType){
if(shapeType == null){
return null;
}
if(shapeType.equalsIgnoreCase("CIRCLE")){
return new Circle();
} else if(shapeType.equalsIgnoreCase("RECTANGLE")){
return new Rectangle();
} else if(shapeType.equalsIgnoreCase("SQUARE")){
return new Square();
}
return null;
}
}
CRTP
静态多态
template
struct base
{
void interface()
{
// ...
static_cast(this)->implementation();
// ...
}
};
struct derived : base
{
void implementation()
{
// ...
}
};
visitor模式
将数据与对数据的操作分离
//前向声明,访问者
class Visitor;
//被访问的抽象类,只有一个接口，用来接受访问者
class Object
{
public:
virtual void accept(Visitor&v) = 0;
};
//具体的被访问的对象，学生。
class StudentA :public Object
{
std::string name;
int score;
public:
StudentA(std::string name_);
int getScore();
std::string getName()
{
return name;
}
void setScore(int num);
virtual void StudentA::accept(Visitor & v)
{
v.visit(this);
}
};
//抽象访问者,只有一个接口，访问.
class Visitor
{
public:
virtual void visit(Object* obj)=0;
};
//具体的访问者一，班主任，实现访问（学生并给学分)
class ClassLeader :public Visitor
{
public:
virtual void visit(Object* obj);
};
//具体的访问者二，校长，实现访问（学生并批评不及格的学生)
class HeadMaster :public Visitor
{
public:
virtual void visit(Object* obj);
};
observer模式
一些观察者观察一个数据，当数据被改动时通知所有观察者
public class Subject {
private List observers
= new ArrayList();
private int state;
public int getState() {
return state;
}
public void setState(int state) {
this.state = state;
notifyAllObservers();
}
public void attach(Observer observer){
observers.add(observer);
}
public void notifyAllObservers(){
for (Observer observer : observers) {
observer.update();
}
}
}
public abstract class Observer {
protected Subject subject;
public abstract void update();
}
public class BinaryObserver extends Observer{
public BinaryObserver(Subject subject){
this.subject = subject;
this.subject.attach(this);
}
@Override
public void update() {
System.out.println( "Binary String: "
+ Integer.toBinaryString( subject.getState() ) );
}
}