Definition

Given a language, define a representation for its grammar along with an interpreter that uses the representation to interpret sentences in the language.

UML class diagram

Participants

• AbstractExpression
  • declares an interface for executing an operation
• TerminalExpression HundredExpression, TenExpression, OneExpression )
  • implements an Interpret operation associated with terminal symbols in the grammar.
  • an instance is required for every terminal symbol in the sentence.
• NonterminalExpression
  • implements an Interpret operation for nonterminal symbols in the grammar.
• Context
  • contains information that is global to the interpreter
• Client
  • builds an abstract syntax tree representing a particular sentence in the language that the grammar defines. The abstract syntax tree is assembled from instances of the NonterminalExpression and TerminalExpression classes
  • invokes the Interpret operation

Sample code in Java

package com.hong.interpreter;

import java.util.ArrayList;

class Context
{
    
}
interface AbstractExpression{
    void interpret(Context context);
}
class TerminalExpression implements AbstractExpression {

    @Override
    public void interpret(Context context) {
        
        System.out.println("Interpret from Terminal-expression");
    }

}
class NonterminalExpression implements AbstractExpression{

    @Override
    public void interpret(Context context) {
        System.out.println("Interpret from Non-terminal expression");
    }

}

public class InterpreterStructure {
    public static void main(String[] args) {
        Context context = new Context(); 
        ArrayList<AbstractExpression> expressions = new ArrayList<AbstractExpression>();
        
        expressions.add(new TerminalExpression());
        expressions.add(new NonterminalExpression());
        expressions.add(new TerminalExpression());
        expressions.add(new TerminalExpression());
        
        for(AbstractExpression exprs : expressions) {
            exprs.interpret(context);
        }
    }

}