解釋器模式 | Interpreter Pattern

解釋器模式提供了評估語言的語法或表達式的方式，它屬於行爲型模式。這種模式實現了一個表達式接口，該接口解釋一個特定的上下文。這種模式被用在 SQL 解析、符號處理引擎等。

創建一個表達式接口：

public interface Expression {
   public boolean interpret(String context);
}

創建實現上述接口的實體類：

public class TerminalExpression implements Expression {

   private String data;

   public TerminalExpression(String data){
      this.data = data; 
   }

   @Override
   public boolean interpret(String context) {
      if(context.contains(data)){
         return true;
      }
      return false;
   }
}

public class OrExpression implements Expression {

   private Expression expr1 = null;
   private Expression expr2 = null;

   public OrExpression(Expression expr1, Expression expr2) { 
      this.expr1 = expr1;
      this.expr2 = expr2;
   }

   @Override
   public boolean interpret(String context) {       
      return expr1.interpret(context) || expr2.interpret(context);
   }
}

public class AndExpression implements Expression {

   private Expression expr1 = null;
   private Expression expr2 = null;

   public AndExpression(Expression expr1, Expression expr2) { 
      this.expr1 = expr1;
      this.expr2 = expr2;
   }

   @Override
   public boolean interpret(String context) {       
      return expr1.interpret(context) && expr2.interpret(context);
   }
}

使用 Expression 類來創建規則，並解析它們。

public class InterpreterPatternDemo {
   //規則：Julie 是一個已婚的女性
   public static Expression getMarriedWomanExpression(){
      Expression julie = new TerminalExpression("Julie");
      Expression married = new TerminalExpression("Married");
      return new AndExpression(julie, married);     
   }

   public static void main(String[] args) {
      Expression isMarriedWoman = getMarriedWomanExpression();

      System.out.println("John is male? " + isMale.interpret("John"));
      System.out.println("Julie is a married women? " 
      + isMarriedWoman.interpret("Married Julie"));
   }
}

輸出：

Julie is a married women? true