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開放封閉原則: 對於擴展是開放的(Open for extension)，對於更改是封閉的(Closed for modification)
建立抽象來隔離以後發生的同類變化:
1. 可擴展性: Operaotor父類別中的GetResult()，抽象化四則運算不同變化。
2. 可複用性: 四則運算子類別分別繼承Operator父類別
3. 可維護性: 工廠模式減低用戶端呼叫的負擔，只需要傳入不同mode，就會傳出適合的運算實體。
運算類別: Operaotor
1: public class Operator
2: {3: private double m_x;
4: private double m_y;
5: public double X {
6: get { return m_x; }
7: set { m_x = value; }
8: }9: public double Y
10: {11: get { return m_y; }
12: set { m_y = value; }
13: }14: public virtual double GetResult()
15: {16: double result = 0;
17: return result;
18: } 19: }運算子類別: +
1: class OperatorAdd : Operator
2: {3: public override double GetResult()
4: {5: double result = 0;
6: result = base.X + base.Y;
7: return result;
8: } 9: }運算子類別:-
1: class OperatorSub : Operator
2: {3: public override double GetResult()
4: {5: double result = 0;
6: result = base.X - base.Y;
7: return result;
8: } 9: }運算子類別:*
1: class OperatorMul: Operator
2: {3: public override double GetResult()
4: {5: double result = 0;
6: result = base.X * base.Y;
7: return result;
8: } 9: }運算子類別:/
1: class OperatorDev:Operator
2: {3: public override double GetResult()
4: {5: double result;
6: if (base.Y == 0)
7: throw new Exception("Cannot divided by zero!");
8: result = base.X / base.Y;
9: return result;
10: } 11: }1: public class OperatorFactory
2: {3: public static Operator createOperator(string op)
4: {5: Operator m_op = null;
6: switch (op)
7: {8: case "+":
9: m_op = new OperatorAdd();
10: break;
11: case "-":
12: m_op = new OperatorSub();
13: break;
14: case "*":
15: m_op = new OperatorMul();
16: break;
17: case "/":
18: m_op = new OperatorDev();
19: break;
20: }21: return m_op;
22: } 23: 24: }用戶端程式碼
1: private void button1_Click(object sender, EventArgs e)
2: { 3: DP.Operator op; 4: op = DP.OperatorFactory.createOperator(comboBox1.Text); 5: op.X = Convert.ToDouble(textBox1.Text); 6: op.Y = Convert.ToDouble(textBox2.Text);7: try {
8: this.Text = op.GetResult().ToString();
9: } catch(Exception ex)
10: { 11: MessageBox.Show(ex.Message.ToString()); 12: } 13: 14: }測試+
測試-
測試*
測試/0
參考資料:
1. 大話設計模式, 作者:程杰
2. [C#] 區分 abstract、virtual、override 和 new
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