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);

 }

}