动机:
在软件构建过程中,如果某一特定领域的问题比较复杂,类似的模式不断重复出现,如果使用普通的编程方式来实现将面临非常频繁的变化。
在这种情况下,将特定领域的问题表达为某种语法规则下的句子,然后构建一个解释器来解释这样的句子,从而达到解决问题的目的。
意图:
给定一个语言,定义它的文法的一种表示,并定义一种解释器,这个解释器使用该表示来解释语言中的句子。
出自:《设计模式》GoF
Interpreter模式的几个要点:
1、Interpreter模式的应用场合是Interpreter模式应用中的难点,只有满足“业务规则频繁变化,且类似的模式重复出现,并且容易抽象为语法的问题”才适合使用Interpreter模式。
2、使用Interpreter模式来表示文法规则,从而可以使用面向对象技巧来方便地“扩展”文法。
3、Interpreter模式比较适合简单的文法表示,对于复杂的文法表示,Interpreter模式会产生比较大的类层次结构,需要求助于语法分析生成器这样的标准工具。
稳定部分:
public abstract class Expression
{
protected Dictionary<string, int> talbe = new Dictionary<string, int>(9);
pulbic Expression()
{
table.Add("一", 1);
table.Add("二", 2);
table.Add("三", 3);
table.Add("四", 4);
table.Add("五", 5);
table.Add("六", 6);
table.Add("七", 7);
table.Add("八", 8);
table.Add("九", 9);
}
public virtual void Interpret(Context context)
{
if (context.Statement.Length == 0)
{
return;
}
foreach (string key in table.Keys)
{
int value = table[key];
if (context.Statement.EndsWith(key + this.GetPostfix()))
{
context.Data += value * this.Multiplier();
context.Statement = context.Statement.Substring(0, context.Statement.Length - this.GetLength);
}
if (context.Statement.EndsWith("零"))
{
context.Statement = context.Statement.Substring(0, context.Statement.Length - 1);
}
}
}
public abstract string GetPostfix();
public abstract int Multiplier();
public virtual int GetLength()
{
return this.GetPostfix().Length + 1;
}
}
{
protected Dictionary<string, int> talbe = new Dictionary<string, int>(9);
pulbic Expression()
{
table.Add("一", 1);
table.Add("二", 2);
table.Add("三", 3);
table.Add("四", 4);
table.Add("五", 5);
table.Add("六", 6);
table.Add("七", 7);
table.Add("八", 8);
table.Add("九", 9);
}
public virtual void Interpret(Context context)
{
if (context.Statement.Length == 0)
{
return;
}
foreach (string key in table.Keys)
{
int value = table[key];
if (context.Statement.EndsWith(key + this.GetPostfix()))
{
context.Data += value * this.Multiplier();
context.Statement = context.Statement.Substring(0, context.Statement.Length - this.GetLength);
}
if (context.Statement.EndsWith("零"))
{
context.Statement = context.Statement.Substring(0, context.Statement.Length - 1);
}
}
}
public abstract string GetPostfix();
public abstract int Multiplier();
public virtual int GetLength()
{
return this.GetPostfix().Length + 1;
}
}
变化部分:
public class GeExpression : Expression
{
public override string GetPostfix()
{
return "";
}
public override int Multiplier()
{
return 10;
}
}
public class ShiExpression : Expression
{
public override string GetPostfix()
{
return "十";
}
public override int Multiplier()
{
return 10;
}
}
public class BaiExpression : Expression
{
public override string GetPostfix()
{
return "百";
}
public override int Multiplier()
{
return 100;
}
}
public class QianExpression : Expression
{
public override string GetPostfix()
{
return "千";
}
public override int Multiplier()
{
return 1000;
}
}
public class WanExpression : Expression
{
public override string GetPostfix()
{
return "万";
}
public override int Multiplier()
{
return 10000;
}
//不能解释"万万"的情况
public override string Interpret(Context context)
{
if (context.Statement.Length == 0)
return;
ArrayList tree = new ArrayList();
tree.Add(new GeExpression());
tree.Add(new ShiExpression());
tree.Add(new BaiExpression());
tree.Add(new QianExpression());
if (context.Statement.EndsWith(this.GetPostfix()))
{
int temp = context.Data;
context.Data = 0;
context.Statement = context.Statement.Substring(0, context.Statement.Length - 1);
foreach (Expression exp in tree)
{
exp.Interpret(context);
}
context.Data = temp + this.Multiplier() * context.Data;
}
}
}
public class Context
{
private string statement;
private int data;
public Context(string statement)
{
this.statement = statement;
}
public string Statement
{
get { return statement; }
set { statement = value; }
}
public string Data
{
get { return data; }
set { data = value; }
}
}
{
public override string GetPostfix()
{
return "";
}
public override int Multiplier()
{
return 10;
}
}
public class ShiExpression : Expression
{
public override string GetPostfix()
{
return "十";
}
public override int Multiplier()
{
return 10;
}
}
public class BaiExpression : Expression
{
public override string GetPostfix()
{
return "百";
}
public override int Multiplier()
{
return 100;
}
}
public class QianExpression : Expression
{
public override string GetPostfix()
{
return "千";
}
public override int Multiplier()
{
return 1000;
}
}
public class WanExpression : Expression
{
public override string GetPostfix()
{
return "万";
}
public override int Multiplier()
{
return 10000;
}
//不能解释"万万"的情况
public override string Interpret(Context context)
{
if (context.Statement.Length == 0)
return;
ArrayList tree = new ArrayList();
tree.Add(new GeExpression());
tree.Add(new ShiExpression());
tree.Add(new BaiExpression());
tree.Add(new QianExpression());
if (context.Statement.EndsWith(this.GetPostfix()))
{
int temp = context.Data;
context.Data = 0;
context.Statement = context.Statement.Substring(0, context.Statement.Length - 1);
foreach (Expression exp in tree)
{
exp.Interpret(context);
}
context.Data = temp + this.Multiplier() * context.Data;
}
}
}
public class Context
{
private string statement;
private int data;
public Context(string statement)
{
this.statement = statement;
}
public string Statement
{
get { return statement; }
set { statement = value; }
}
public string Data
{
get { return data; }
set { data = value; }
}
}
主程序:
public static void Main()
{
string roman = "五十七万六千四百五十二"; //==>576452
Context context = new Context(roman);
ArrayList tree = new ArrayList();
tree.Add(new GeExpression());
tree.Add(new ShiExpression());
tree.Add(new BaiExpression());
tree.Add(new QianExpression());
tree.Add(new WanExpression());
foreach (Expression exp in tree)
{
exp.Interpret(context);
}
Console.WriteLine("{0} = {1}",roman, context.Data);
}
{
string roman = "五十七万六千四百五十二"; //==>576452
Context context = new Context(roman);
ArrayList tree = new ArrayList();
tree.Add(new GeExpression());
tree.Add(new ShiExpression());
tree.Add(new BaiExpression());
tree.Add(new QianExpression());
tree.Add(new WanExpression());
foreach (Expression exp in tree)
{
exp.Interpret(context);
}
Console.WriteLine("{0} = {1}",roman, context.Data);
}