设计模式 - 解释器模式

解释器模式提供了一种评估语言语法或表达式的途径。这种类型的模式属于行为型模式。此模式涉及实现一个表达式接口，该接口指示解释特定上下文。此模式用于 SQL 解析、符号处理引擎等。

实现

我们将创建一个接口Expression和实现Expression接口的具体类。定义了一个类TerminalExpression，它充当所讨论上下文的解释器。其他类OrExpression、AndExpression用于创建组合表达式。

InterpreterPatternDemo（我们的演示类）将使用Expression类来创建规则并演示表达式的解析。

步骤 1

创建一个表达式接口。

Expression.java

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

步骤 2

创建实现上述接口的具体类。

TerminalExpression.java

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;
   }
}

OrExpression.java

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);
   }
}

AndExpression.java

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);
   }
}

步骤 3

InterpreterPatternDemo使用Expression类来创建规则，然后解析它们。

InterpreterPatternDemo.java

public class InterpreterPatternDemo {

   //Rule: Robert and John are male
   public static Expression getMaleExpression(){
      Expression robert = new TerminalExpression("Robert");
      Expression john = new TerminalExpression("John");
      return new OrExpression(robert, john);		
   }

   //Rule: Julie is a married women
   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 isMale = getMaleExpression();
      Expression isMarriedWoman = getMarriedWomanExpression();

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

步骤 4

验证输出。

John is male? true
Julie is a married women? true