设计模式学习15 Interpreter

应用场景：

Given a language, define a representation for its grammar along with an interpreter that uses the representation to interpret sentences in the language.

给定一个语言，定义它的发文的一种的表示，并定义一种解释器，使用这个解释器来解释这些句子。

实现代码：

class Program { static void Main(string[] args) { string roman = "MCMXXVIII"; Context context = new Context(roman); // Build the 'parse tree' List<Expression> tree = new List<Expression>(); tree.Add(new ThousandExpression()); tree.Add(new HundredExpression()); tree.Add(new TenExpression()); tree.Add(new OneExpression()); // Interpret foreach (Expression exp in tree) { exp.Interpret(context); } Console.WriteLine("{0} = {1}", roman, context.Output); Console.ReadKey(); } } class Context { private string input; private int output; public Context(string input) { this.input = input; } public string Input { get { return this.input; } set { this.input = value; } } public int Output { get { return this.output; } set { this.output = value; } } } abstract class Expression { public void Interpret(Context context) { if (context.Input.Length == 0) return; if (context.Input.StartsWith(Nine())) { context.Output += (9 * Multiplier()); // 解释这个字符串 context.Input = context.Input.Substring(2); } else if (context.Input.StartsWith(Four())) { context.Output += (4 * Multiplier()); context.Input = context.Input.Substring(2); } else if (context.Input.StartsWith(Five())) { context.Output += (5 * Multiplier()); context.Input = context.Input.Substring(1); } while (context.Input.StartsWith(One())) { context.Output += (1 * Multiplier()); context.Input = context.Input.Substring(1); } } public abstract string One(); public abstract string Four(); public abstract string Five(); public abstract string Nine(); public abstract int Multiplier(); } class ThousandExpression : Expression { public override string One() { return "M"; } public override string Four() { return " "; } public override string Five() { return " "; } public override string Nine() { return " "; } public override int Multiplier() { return 1000; } } class HundredExpression : Expression { public override string One() { return "C"; } public override string Four() { return "CD"; } public override string Five() { return "D"; } public override string Nine() { return "CM"; } public override int Multiplier() { return 100; } } class TenExpression : Expression { public override string One() { return "X"; } public override string Four() { return "XL"; } public override string Five() { return "L"; } public override string Nine() { return "XC"; } public override int Multiplier() { return 10; } } class OneExpression : Expression { public override string One() { return "I"; } public override string Four() { return "IV"; } public override string Five() { return "V"; } public override string Nine() { return "IX"; } public override int Multiplier() { return 1; } }