Improve visitor usage

src/main/java/interpreter/Evaluator.java

@@ -34,23 +34,22 @@ takes an `Expression` in the constructor and provides a method `eval()` which ev
 the given expression and returns the result as an integer. For a given `expression` of type `Expression`
 it can be used as follows
 
-    Evaluator evaluator = new Evaluator(expression)
-    System.out.println(evaluator.eval());
+    Evaluator evaluator = new Evaluator(expression, valuation)
+    System.out.println(evaluator.getValue());
 
 The evaluation function `eval` takes the variable valuation `v`, which is passed on recursively. As the valuation
 is not changed during the evaluation process, it can be stored in a global variable which is not changed. */
 public class Evaluator extends Visitor<Integer> {
-
-    final Expression expression;
-    final Map<String, Integer> valuation = new HashMap<String, Integer>();
+    private final int value;
+    private final Map<String, Integer> valuation = new HashMap<String, Integer>();
 
     public Evaluator(Expression expression, Map<String, Integer> valuation) {
-        this.expression = expression;
         this.valuation.putAll(valuation);
+        value = visit(expression);
     }
 
-    public int eval() {
-        return visit(expression);
+    public int getValue() {
+        return value;
     }
 
     /*!

src/main/java/interpreter/Interpreter.java

@@ -49,8 +49,7 @@ The semantic function `sem` passes along the variable valuation `v`. In the `Int
 as global variable `valuation`. Because of the in-order execution this global variable always represents the state
 of the `v` passed to the semantic function `sem`. */
 public class Interpreter extends Visitor {
-    final Program program;
-    final Map<String, Integer> valuation = new HashMap<String, Integer>();
+    private final Map<String, Integer> valuation = new HashMap<String, Integer>();
 
     public Map<String, Integer> getValuation() {
         Map<String, Integer> result = new HashMap<String, Integer>();
@@ -59,7 +58,6 @@ public class Interpreter extends Visitor {
     }
 
     public Interpreter(Program program) {
-        this.program = program;
         visit(program);
     }
 
@@ -68,7 +66,7 @@ public class Interpreter extends Visitor {
     */
     public void visitAssignment(Assignment assignment) {
         Evaluator evaluator = new Evaluator(assignment.expression, valuation);
-        valuation.put(assignment.identifier.name, evaluator.eval());
+        valuation.put(assignment.identifier.name, evaluator.getValue());
     }
 
     /*!
@@ -86,7 +84,7 @@ public class Interpreter extends Visitor {
     */
     public void visitConditional(Conditional conditional) {
         Evaluator evaluator = new Evaluator(conditional.condition, valuation);
-        if (evaluator.eval() != 0) {
+        if (evaluator.getValue() != 0) {
             visit(conditional.thenCase);
         } else {
             visit(conditional.elseCase);
@@ -100,7 +98,7 @@ public class Interpreter extends Visitor {
     */
     public void visitLoop(Loop loop) {
         Evaluator evaluator = new Evaluator(loop.condition, valuation);
-        if (evaluator.eval() != 0) {
+        if (evaluator.getValue() != 0) {
             visit(new Composition(loop.program, loop));
         }
     }

src/test/java/interpreter/EvaluatorTest.java

@@ -16,6 +16,6 @@ public class EvaluatorTest {
         valuation.put("y", 2);
         Expression expression = new Addition(new Identifier("x"), new Subtraction(new Identifier("y"), new Int(-4)));
         Evaluator evaluator = new Evaluator(expression, valuation);
-        assertEquals(13, evaluator.eval());
+        assertEquals(13, evaluator.getValue());
     }
 }