简单工厂模式－－加减乘除运算

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：

 1 #import <Foundation/Foundation.h>
 2  3 @interface Operation : NSObject
 4  5 @property double a;
 6 @property double b;
 7 @property double result;
 8 -(double)getResult:(double)a second:(double)b;
 9 10 @end 11 12 //>>>>>>>>>>>>>>>>>>>>>>><<<<<<<<<<<<<<<<<<<<<<<<<<< 13 14 #import "Operation.h" 15 16 @implementation Operation
17 18 -(double)getResult:(double)a second:(double)b{
19 self.a = a;
20 self.b = b;
21 return self.a+self.b;
22 };
23 24 @end

 1 #import "Operation.h"  2  3 @interface SubOperation : Operation
 4  5 @end  6  7 //>>>>>>>>>>>>>>>>>>>>>>>><<<<<<<<<<<<<<<<<<<<<<<<<<  8  9 #import "SubOperation.h" 10 11 @implementation SubOperation
12 13 -(double)getResult:(double)a second:(double)b{
14 self.a = a;
15 self.b = b;
16 self.result = self.a - self.b;
17 return self.result;
18 }
19 20 @end

 1 #import "Operation.h"  2  3 @interface AddOperation : Operation
 4  5 @end  6  7 #import "AddOperation.h"  8  9 @implementation AddOperation
10 11 -(double)getResult:(double)a second:(double)b{
12 self.a = a;
13 self.b = b;
14 15 self.result = self.a + self.b;
16 return self.result;
17 };
18 19 @end

 1 #import "Operation.h"  2  3 @interface MulOperation : Operation
 4  5 @end  6  7  8 #import "MulOperation.h"  9 10 @implementation MulOperation
11 12 -(double)getResult:(double)a second:(double)b{
13 self.a = a;
14 self.b = b;
15 16 self.result = self.a * self.b;
17 return self.result;
18 }
19 @end

 1 #import "Operation.h"  2  3 @interface DivOperation : Operation
 4  5 @end  6  7 #import "DivOperation.h"  8  9 @implementation DivOperation
10 11 -(double)getResult:(double)a second:(double)b{
12 self.a = a;
13 self.b = b;
14 if (self.b == 0) {
15 NSLog(@"除数不能为0");
16 return 0;
17  }
18 self.result = self.a / self.b;
19 return self.result;
20 }
21 22 @end

 1 #import <Foundation/Foundation.h>
 2 #import "Operation.h"  3 @interface OperationFactory : NSObject
 4 +(Operation*)creatOperation:(NSString*)str;
 5 @end  6  7 //>>>>>>>>>>>>>>>>>>>>>><<<<<<<<<<<<<<<<<<<<<<<<<<<<  8  9 #import "OperationFactory.h" 10 #import "AddOperation.h" 11 #import "SubOperation.h" 12 #import "MulOperation.h" 13 #import "DivOperation.h" 14 @implementation OperationFactory
15 16 +(Operation*)creatOperation:(NSString*)str{
17 Operation *oper = NULL;
18 if ([str isEqual: @"+"]) {
19 oper = [[AddOperation alloc] init];
20 }else if ([str isEqual: @"-"]) {
21 oper = [[SubOperation alloc] init];
22 }else if ([str isEqual: @"*"]) {
23 oper = [[MulOperation alloc] init];
24 }else if ([str isEqual: @"/"]) {
25 oper = [[DivOperation alloc] init];
26 }else {
27 NSLog(@"输入无效的内容");
28  }
29 return oper;
30 }
31 32 @end

 1 #import <Foundation/Foundation.h>
 2 #import "OperationFactory.h"  3 int main(int argc, const char * argv[]) {
 4  @autoreleasepool {
 5 // insert code here...  6 Operation *op = [OperationFactory creatOperation:@"+"];
 7 NSLog(@"简单工厂模式算出结果%f",[op getResult:18 second:8]);
 8 Operation *op2 = [OperationFactory creatOperation:@"/"];
 9 NSLog(@"简单工厂模式算除法%f",[op2 getResult:18 second:0]);
10 NSLog(@"Hello, World!");
11  }
12 return 0;
13 }

运行结果：