add expressions

Author: h908714124

src/main/java/io/polypen/Expressions.java

@@ -0,0 +1,21 @@
+package io.polypen;
+
+import java.util.List;
+
+public class Expressions {
+    public sealed interface Expression permits Product {
+        String eval();
+    }
+
+    public record Product(List<String> factors) implements Expression {
+        @Override
+        public String eval() {
+            List<Polynomial> polynomials = factors.stream().map(Polynomial::parse).toList();
+            Polynomial result = Polynomial.ONE;
+            for (Polynomial p : polynomials) {
+                result = result.multiply(p);
+            }
+            return result.toString();
+        }
+    }
+}

src/main/java/io/polypen/Main.java

@@ -1,26 +1,19 @@
 package io.polypen;
 
-import java.util.List;
+import io.polypen.Expressions.Expression;
+
 import java.util.Scanner;
 
 public class Main {
 
-    public static Polynomial evalProduct(String s) {
-        List<Polynomial> polynomials = Parser.parseProduct(s).stream().map(Polynomial::parse).toList();
-        Polynomial result = Polynomial.ONE;
-        for (Polynomial p : polynomials) {
-            result = result.multiply(p);
-        }
-        return result;
-    }
-
     public static void main(String[] args) {
         Scanner in = new Scanner(System.in);
         StringBuilder sb = new StringBuilder();
         while (in.hasNextLine()) {
             String line = in.nextLine();
             sb.append(line);
         }
-        System.out.println(evalProduct(sb.toString()));
+        Expression expression = Parser.parseProduct(sb.toString());
+        System.out.println(expression.eval());
     }
 }

src/main/java/io/polypen/Parser.java

@@ -1,5 +1,7 @@
 package io.polypen;
 
+import io.polypen.Expressions.Expression;
+import io.polypen.Expressions.Product;
 import org.apache.commons.numbers.fraction.Fraction;
 
 import java.util.ArrayList;
@@ -43,7 +45,7 @@ static List<Fraction> parsePolynomial(String s) {
         return result;
     }
 
-    static List<String> parseProduct(String s) {
+    static Expression parseProduct(String s) {
         List<String> result = new ArrayList<>();
         StringBuilder sb = new StringBuilder();
         int nestingLevel = -1;
@@ -74,7 +76,7 @@ static List<String> parseProduct(String s) {
         if (!sb.isEmpty()) {
             result.add(sb.toString());
         }
-        return result;
+        return new Product(result);
     }
 
     enum Sign {

src/test/java/io/polypen/PolynomialTest.java

@@ -1,12 +1,14 @@
 package io.polypen;
 
+import io.polypen.Expressions.Expression;
 import org.apache.commons.numbers.fraction.Fraction;
 import org.junit.jupiter.api.Test;
 
 import java.util.List;
 
 import static io.polypen.Polynomial.parse;
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertInstanceOf;
 
 class PolynomialTest {
 
@@ -39,7 +41,9 @@ void monomialMultiplication() {
 
     @Test
     void parseProduct() {
-        List<String> strings = Parser.parseProduct("(a + 1) * (a - 1)");
-        assertEquals(List.of("a + 1", "a - 1"), strings);
+        Expression expression = Parser.parseProduct("(a + 1) * (a - 1)");
+        assertInstanceOf(Expressions.Product.class, expression);
+        Expressions.Product product = (Expressions.Product) expression;
+        assertEquals(List.of("a + 1", "a - 1"), product.factors());
     }
 }