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Design Patterns in Java (Behavioral) - Interpreter Pattern

Interpreter Pattern

  • Represent grammar
  • Interpret a sentence
  • Map a domain



Main







 static Expression buildInterpreter(){





  





  Expression e = new TerminalEpression("lion");





  Expression e1 = new TerminalEpression("bear");





  Expression e2 = new AndExpression(e, e1);





  return e2;





 }





 



 public static void main(String[] args) {





  



  String expression = "lion";





  String context = "lion bea2r";

  





  Expression e = buildInterpreter();







  System.out.println(context + " is " + e.interpeter(context) );  





 }

Interface (Abstract expression)

public interface Expression {

public boolean interpeter(String context);
}

Terminal Expression



public class TerminalEpression implements Expression {






 private String data; 



 public TerminalEpression(String data){



  this.data = data;



 }



 



 @Override



 public boolean interpeter(String context) {



  StringTokenizer st = new StringTokenizer(context);



  



  while (st.hasMoreTokens()) {



   String test = st.nextToken();



   if(test.equals(data)){



    return true;



   }



  } 



  return false;



 }



}

NonTerminal Expression



public class AndExpression implements Expression {










 private Expression exp1;



 private Expression exp2;







 public AndExpression(Expression exp1, Expression exp2){

  this.exp1 = exp1;



  this.exp2 = exp2;



 }



 @Override



 public boolean interpeter(String context) {



  return exp1.interpeter(context) && exp2.interpeter(context);



 }



}




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