Refactoring InterpreterPattern.

chrish · chrish · commit b9e9383dec73 · 2017-10-24T16:46:34.000+08:00
diff --git a/Behavioral/InterpreterPattern/src/io/csie/chris/Evaluator.java b/Behavioral/InterpreterPattern/src/io/csie/chris/Evaluator.java
@@ -1,9 +1,6 @@
 package io.csie.chris;
 
-import io.csie.chris.expression.Expression;
-import io.csie.chris.expression.Minus;
-import io.csie.chris.expression.Plus;
-import io.csie.chris.expression.Variable;
+import io.csie.chris.expression.*;
 
 import java.util.Map;
 import java.util.Stack;
@@ -12,23 +9,32 @@ public class Evaluator implements Expression {
 
     private Expression syntaxTree;
 
-    public Evaluator(final String expression) {
+    Evaluator(final String expression) {
 
-        final Stack<Expression> expressionStack = new Stack<Expression>();
+        final Stack<Expression> expressionStack = new Stack<>();
 
         for (final String token : expression.split(" ")) {
-            if (token.equals("+")) {
-                final Expression subExpression = new Plus(expressionStack.pop(), expressionStack.pop());
-                expressionStack.push(subExpression);
-            } else if (token.equals("-")) {
-                // it's necessary remove first the right operand from the stack
-                final Expression right = expressionStack.pop();
-                // ..and after the left one
-                final Expression left = expressionStack.pop();
-                final Expression subExpression = new Minus(left, right);
-                expressionStack.push(subExpression);
-            } else
-                expressionStack.push(new Variable(token));
+            switch (token) {
+                case "+":
+                    final Expression addExpression = new Plus(expressionStack.pop(), expressionStack.pop());
+                    expressionStack.push(addExpression);
+                    break;
+                case "-":
+                    // it's necessary remove first the right operand from the stack
+                    final Expression right = expressionStack.pop();
+                    // ..and after the left one
+                    final Expression left = expressionStack.pop();
+                    final Expression subExpression = new Minus(left, right);
+                    expressionStack.push(subExpression);
+                    break;
+                case "*":
+                    final Expression multiExpression = new Multiplication(expressionStack.pop(), expressionStack.pop());
+                    expressionStack.push(multiExpression);
+                    break;
+                default:
+                    expressionStack.push(new Variable(token));
+                    break;
+            }
         }
         syntaxTree = expressionStack.pop();
     }
diff --git a/Behavioral/InterpreterPattern/src/io/csie/chris/Main.java b/Behavioral/InterpreterPattern/src/io/csie/chris/Main.java
@@ -10,12 +10,13 @@ public class Main {
 
     public static void main(final String[] args) {
 
-        final String expression = "w x z - +";
+        final String expression = "v w x z - + *";
 
         final Evaluator sentence = new Evaluator(expression);
 
         final Map<String, Expression> variables = new HashMap<>();
 
+        variables.put("v", new Number(2));
         variables.put("w", new Number(5));
         variables.put("x", new Number(10));
         variables.put("z", new Number(42));
diff --git a/Behavioral/InterpreterPattern/src/io/csie/chris/expression/Multiplication.java b/Behavioral/InterpreterPattern/src/io/csie/chris/expression/Multiplication.java
@@ -0,0 +1,20 @@
+package io.csie.chris.expression;
+
+import java.util.Map;
+
+public class Multiplication implements Expression{
+
+    private Expression leftOperand;
+
+    private Expression rightOperand;
+
+    public Multiplication(Expression leftOperand, Expression rightOperand) {
+        this.leftOperand = leftOperand;
+        this.rightOperand = rightOperand;
+    }
+
+    @Override
+    public int interpret(Map<String, Expression> variables) {
+        return leftOperand.interpret(variables) * rightOperand.interpret(variables);
+    }
+}
