通過多型製作一個簡單的計算器

Operation類：

 1    public class Operation
 2     {
 3         private double _numberA = 0;
 4         private double _numberB = 0;
 5         public double NumberA
 6         {
 7             get
 8             {
 9                 return _numberA;
10             }
11 
12             set
 

13             {
14                 _numberA = value;
15             }
16         }
17         public double NumberB
18         {
19             get
20             {
21                 return _numberB;
22             }
23 
24             set
25             {
26                 _numberB = value;
27             }
 
28         }
29         public virtual double GetResult()
30         {
31             double result = 0;
32             return result;
33         }
34     }

簡單工廠類：

 1 public class OperationFactory
 2     {
 3         public static Operation createOperate(string operate)
 4
 
         {
 5             Operation oper = null;
 6             switch (operate)
 7             {
 8                 case "+":
 9                     oper = new OperationAdd();
10                     break;
11                 case "-":
12                     oper = new OperationSub();
13                     break;
14                 case "*":
15                     oper = new OperationMul();
16                     break;
17                 case "/":
18                     oper = new OperationDiv();
19                     break;
20             }
21             return oper;
22         }
23     }

加法類，繼承Operation：

1 class OperationAdd:Operation
2     {
3         public override double GetResult()
4         {
5             double result = 0;
6             result = NumberA + NumberB;
7             return result;
8         }
9     }

減法類，繼承Operation：

1     class OperationSub:Operation
2     {
3         public override double GetResult()
4         {
5             double result = 0;
6             result = NumberA - NumberB;
7             return result;
8         }
9     }

乘法類，繼承Operation：

1     class OperationMul : Operation
2     {
3         public override double GetResult()
4         {
5             double result = 0;
6             result = NumberA * NumberB;
7             return result;
8         }
9     }

除法類，繼承Operation：

 1     class OperationDiv : Operation
 2     {
 3         public override double GetResult()
 4         {
 5             double result = 0;
 6             if (NumberB==0)
 7             {
 8                 throw new Exception("除數不能為0。");
 9             }
10             result = NumberA / NumberB;
11             return result;
12         }
13     }

呼叫：

1         private void button1_Click(object sender, EventArgs e)
2         {
3             Operation oper = OperationFactory.createOperate(textBox4.Text);
4             oper.NumberA =Convert.ToDouble(textBox1.Text);
5             oper.NumberB = Convert.ToDouble(textBox2.Text);
6             textBox3.Text = oper.GetResult().ToString();
7         }