简单工厂模式－－加减乘除运算

学习来自《大话设计模式》

下面基于简单的<加减乘除运算>实例来讲讲实用简单工厂模式：<备注：以后根据认识的加深，可以添加和修改内容>

需求分析：希望程序提供“加减乘除”四种功能。

功能分析：四种功能都是并列的，相互独立的。

拓展分析：很有可能拓展新的功能，比如“开根运算”。

如何设计：

1、根据“功能分析”可以将四种功能都归并一个父类出来，然后创建四个子类继承它，并且提供空的方法（OC中模拟抽象方法或者虚函数），这四个子类分别都要继承并重写实现这个空方法。这样，一个抽象的父类，四个具体实现的子类，就可以形成多态的应用：父类声明，子类创建实例。

2、然后创建一个工厂类与功能的抽象父类相互关联，然后实现根据需求，应用多态来创建功能的实例。

3、拓展：如果需要添加“开根”的功能，只要添加一个继承运算类的子类，然后在简单工厂类创建方法中添加修改一点。

 附加代码：

#import <Foundation/Foundation.h>

@interface Operation : NSObject

@property double a;
@property double b;
@property double result;
-(double)getResult:(double)a second:(double)b;

@end

//>>>>>>>>>>>>>>>>>>>>>>><<<<<<<<<<<<<<<<<<<<<<<<<<<

#import "Operation.h"

@implementation Operation

-(double)getResult:(double)a second:(double)b{
    self.a = a;
    self.b = b;
    return self.a+self.b;
};

@end

#import "Operation.h"

@interface SubOperation : Operation

@end

//>>>>>>>>>>>>>>>>>>>>>>>><<<<<<<<<<<<<<<<<<<<<<<<<<

#import "SubOperation.h"

@implementation SubOperation

-(double)getResult:(double)a second:(double)b{
    self.a = a;
    self.b = b;
    self.result = self.a - self.b;
    return self.result;
}

@end

#import "Operation.h"

@interface AddOperation : Operation

@end

#import "AddOperation.h"

@implementation AddOperation

-(double)getResult:(double)a second:(double)b{
    self.a = a;
    self.b = b;

    self.result = self.a + self.b;
    return self.result;
};

@end

#import "Operation.h"

@interface MulOperation : Operation

@end


#import "MulOperation.h"

@implementation MulOperation

-(double)getResult:(double)a second:(double)b{
    self.a = a;
    self.b = b;

    self.result = self.a * self.b;
    return self.result;
}
@end

#import "Operation.h"

@interface DivOperation : Operation

@end

#import "DivOperation.h"

@implementation DivOperation

-(double)getResult:(double)a second:(double)b{
    self.a = a;
    self.b = b;
    if (self.b == 0) {
        NSLog(@"除数不能为0");
        return 0;
    }
    self.result = self.a / self.b;
    return self.result;
}

@end

#import <Foundation/Foundation.h>
#import "Operation.h"
@interface OperationFactory : NSObject
+(Operation*)creatOperation:(NSString*)str;
@end

//>>>>>>>>>>>>>>>>>>>>>><<<<<<<<<<<<<<<<<<<<<<<<<<<<

#import "OperationFactory.h"
#import "AddOperation.h"
#import "SubOperation.h"
#import "MulOperation.h"
#import "DivOperation.h"
@implementation OperationFactory

+(Operation*)creatOperation:(NSString*)str{
    Operation *oper = NULL;
    if ([str  isEqual: @"+"]) {
        oper = [[AddOperation alloc] init];
    }else if ([str isEqual: @"-"]) {
        oper = [[SubOperation alloc] init];
    }else if ([str isEqual: @"*"]) {
        oper = [[MulOperation alloc] init];
    }else if ([str isEqual: @"/"]) {
        oper = [[DivOperation alloc] init];
    }else {
        NSLog(@"输入无效的内容");
    }
    return oper;
}

@end

#import <Foundation/Foundation.h>
#import "OperationFactory.h"
int main(int argc, const char * argv[]) {
    @autoreleasepool {
        // insert code here...
        Operation *op = [OperationFactory creatOperation:@"+"];
        NSLog(@"简单工厂模式算出结果%f",[op getResult:18 second:8]);
        Operation *op2 = [OperationFactory creatOperation:@"/"];
        NSLog(@"简单工厂模式算除法%f",[op2 getResult:18 second:0]);
        NSLog(@"Hello, World!");
    }
    return 0;
}

运行结果：