2022-05-12-인터프리터패턴-2부-패턴적용하기

01.소스코드

01.1 App

import java.util.Map;

public class App {

    public static void main(String[] args) {
        PostfixExpression expression = PostfixParser.parse("xyz+-a+");
        int result = expression.interpret(Map.of('x', 1, 'y', 2, 'z', 3, 'a', 4));
        System.out.println(result);
    }
}

01.2 PostfixExpression

import java.util.Map;

public interface PostfixExpression {

    int interpret(Map<Character, Integer> context);

}

01.3 VariableExpression

import java.util.Map;

public class VariableExpression implements PostfixExpression {

    private Character character;

    public VariableExpression(Character character) {
        this.character = character;
    }

    @Override
    public int interpret(Map<Character, Integer> context) {
        return context.get(this.character);
    }
}

01.4 PlusExpression

public class PlusExpression implements PostfixExpression {

    private PostfixExpression left;

    private PostfixExpression right;

    public PlusExpression(PostfixExpression left, PostfixExpression right) {
        this.left = left;
        this.right = right;
    }

    @Override
    public int interpret(Map<Character, Integer> context) {
        return left.interpret(context) + right.interpret(context);
    }
}

01.5 MinusExpression

import java.util.Map;

public class MinusExpression implements PostfixExpression {

    private PostfixExpression left;

    private PostfixExpression right;

    public MinusExpression(PostfixExpression left, PostfixExpression right) {
        this.left = left;
        this.right = right;
    }

    @Override
    public int interpret(Map<Character, Integer> context) {
        return left.interpret(context) - right.interpret(context);
    }
}

01.6 PostfixParser

import java.util.Stack;

import static me.whiteship.designpatterns._03_behavioral_patterns._15_interpreter._02_after.PostfixExpression.*;

public class PostfixParser {

    public static PostfixExpression parse(String expression) {
        Stack<PostfixExpression> stack = new Stack<>();
        for (char c : expression.toCharArray()) {
            stack.push(getExpression(c, stack));
        }
        return stack.pop();
    }

    private static PostfixExpression getExpression(char c, Stack<PostfixExpression> stack) {
        switch (c) {
            case '+':
                return new PlusExpression(stack.pop(), stack.pop());
            case '-':
                PostfixExpression right = stack.pop();
                PostfixExpression left = stack.pop();
                return new MinusExpression(left, right);
            default:
                return new VariableExpression(c);
        }
    }
}

02.다른 사용법

02.1 PostfixExpression

• before

• import java.util.Map;
  
  public interface PostfixExpression {
  
      int interpret(Map<Character, Integer> context);
  
  }

• after
  • 위와 같이 하면 Plus, Minus, Variable이 없어도됨

• import java.util.Map;
  
  public interface PostfixExpression {
  
      int interpret(Map<Character, Integer> context);
  	
      static PostfixExpression plus(PostfixExpression left, PostfixExpression right){	
  		return new PostfixExpression(){
  			@Override
              public int interpret(Map<character, Integer> context){
                  return left.interpret(context) + right.interpret(context);
              }
          };
      }
      /*
      static PostfixExpression plus(PostfixExpression left, PostfixExpression right){
  	 	return context -> left.interpret(context) + right.interpret(context);
      }
      *///람다 표현식
      
      static PostfixExpression minus(PostfixExpression left, PostfixExpression right){
  	 	return context -> left.interpret(context) + right.interpret(context);
      }
      
      static PostfixExpression variable(Character c){
          return context -> context.get(c);
      }
  }

02.2 PostfixParser

• before

• import java.util.Stack;
  
  import static me.whiteship.designpatterns._03_behavioral_patterns._15_interpreter._02_after.PostfixExpression.*;
  
  public class PostfixParser {
  
      public static PostfixExpression parse(String expression) {
          Stack<PostfixExpression> stack = new Stack<>();
          for (char c : expression.toCharArray()) {
              stack.push(getExpression(c, stack));
          }
          return stack.pop();
      }
  
      private static PostfixExpression getExpression(char c, Stack<PostfixExpression> stack) {
          switch (c) {
              case '+':
                  return new PlusExpression(stack.pop(), stack.pop());
              case '-':
                  PostfixExpression right = stack.pop();
                  PostfixExpression left = stack.pop();
                  return new MinusExpression(left, right);
              default:
                  return new VariableExpression(c);
          }
      }
  }

• after

• import java.util.Stack;
  
  import static me.whiteship.designpatterns._03_behavioral_patterns._15_interpreter._02_after.PostfixExpression.*;
  
  public class PostfixParser {
  
      public static PostfixExpression parse(String expression) {
          Stack<PostfixExpression> stack = new Stack<>();
          for (char c : expression.toCharArray()) {
              stack.push(getExpression(c, stack));
          }
          return stack.pop();
      }
  
      private static PostfixExpression getExpression(char c, Stack<PostfixExpression> stack) {
          switch (c) {
              case '+':
                  return new PostfixExpression.plus(stack.pop(), stack.pop());
              case '-':
                  PostfixExpression right = stack.pop();
                  PostfixExpression left = stack.pop();
                  return PostfixExpression.minus(left, right);
              default:
                  return PostfixExpression.variable(c);
          }
      }
  }

https://github.com/3DPIT/3dpit.github.io/blob/main/content/blog/DesignPattern/2022-05-12-%EC%9D%B8%ED%84%B0%ED%94%84%EB%A6%AC%ED%84%B0%ED%8C%A8%ED%84%B4-2%EB%B6%80-%ED%8C%A8%ED%84%B4%EC%A0%81%EC%9A%A9%ED%95%98%EA%B8%B0.md

GitHub - 3DPIT/3dpit.github.io