简单工厂模式

#include <iostream>

using namespace std;

/* Operation 基类和子类 */
class Operation {

public:
    void setOperands(const int operA = 0, const int operB = 0) {m_operandA = operA; m_operandB = operB;}
    virtual int getRlt() = 0;

protected:
    int m_operandA;
    int m_operandB;
};

class OperationAdd : public Operation {
public:
    int getRlt() {return m_operandA + m_operandB;}
};

class OperationSub : public Operation {
public:
    int getRlt() {return m_operandA - m_operandB;}
};

/* SimpleFactory 类 */
class SimpleFactory {
public:
    static Operation* createOperation(char oper);
};

Operation* SimpleFactory::createOperation(char oper) {
    Operation *operation = NULL;
    switch (oper) {
    case '+':
        operation = new OperationAdd();
        break;
    case '-':
        operation = new OperationSub();
        break;
    }
    return operation;
}

/* 测试 */
void main() {
    Operation *oper = NULL;
    oper = SimpleFactory::createOperation('+');
    oper->setOperands(32, 23);
    cout<<"Result: "<<oper->getRlt()<<endl;
    delete oper;

    oper = SimpleFactory::createOperation('-');
    oper->setOperands(32, 23);
    cout<<"Result: "<<oper->getRlt()<<endl;
    delete oper;

    system("pause");
}

基本思想：

为什么使用simple factory模式？

当基类的派生类很多时，比如OperationAdd，OperationSub, OperationMulti etc. 使用它们时需要通过各个名字来创建，

如果使用simple facotry类来管理，对用户而言

1. 逻辑就更清晰

2. 更抽象，对用户隐藏了各个派生类。

对开发者而言，逻辑同样更清晰了，易于维护。