First try with visitors

src/main/java/Main.java

@@ -48,6 +48,6 @@ public class Main {
         semanticAnalyzer.analyze(ast);
 
         ByteCodeGenerator byteCodeGenerator = new ByteCodeGenerator();
-        byteCodeGenerator.generateByteCode(ast);
+        byteCodeGenerator.visit(ast);
     }
 }

src/main/java/ast/ClassNode.java

@@ -5,10 +5,12 @@ import ast.member.MemberNode;
 import ast.type.AccessTypeNode;
 import ast.type.EnumAccessTypeNode;
 
+import bytecode.visitor.ClassVisitor;
+import bytecode.visitor.Visitable;
 import java.util.ArrayList;
 import java.util.List;
 
-public class ClassNode extends ASTNode{
+public class ClassNode extends ASTNode implements Visitable {
     public IdentifierNode identifier;
     public AccessTypeNode accessType;
     public String name;
@@ -33,4 +35,9 @@ public class ClassNode extends ASTNode{
             members.add(0,constructor);
         }
     }
+
+    @Override
+    public void accept(ClassVisitor classVisitor) {
+        classVisitor.visit(this);
+    }
 }

src/main/java/ast/ProgramNode.java

@@ -1,12 +1,19 @@
 package ast;
 
+import bytecode.visitor.ProgramVisitor;
+import bytecode.visitor.Visitable;
 import java.util.ArrayList;
 import java.util.List;
 
-public class ProgramNode extends ASTNode {
+public class ProgramNode extends ASTNode implements Visitable {
     public List<ClassNode> classes = new ArrayList<>();
 
     public void addClass(ClassNode classNode) {
         classes.add(classNode);
     }
+
+    @Override
+    public void accept(ProgramVisitor programVisitor) {
+        programVisitor.visit(this);
+    }
 }

src/main/java/bytecode/ByteCodeGenerator.java

@@ -2,13 +2,15 @@ package bytecode;
 
 import ast.ProgramNode;
 import ast.ClassNode;
+import bytecode.visitor.ProgramVisitor;
 
-public class ByteCodeGenerator {
+public class ByteCodeGenerator implements ProgramVisitor {
 
-  public void generateByteCode(ProgramNode ast) {
-    for (ClassNode classDeclarationNode : ast.classes) {
+  @Override
+  public void visit(ProgramNode programNode) {
+    for (ClassNode classDeclarationNode : programNode.classes) {
       ClassCodeGen classCodeGen = new ClassCodeGen();
-      classCodeGen.generateClassCode(classDeclarationNode);
+      classDeclarationNode.accept(classCodeGen);
     }
   }
 }

src/main/java/bytecode/ClassCodeGen.java

@@ -1,9 +1,12 @@
 package bytecode;
 
 import ast.ClassNode;
+import ast.ProgramNode;
 import ast.member.FieldNode;
 import ast.member.MemberNode;
 import ast.member.MethodNode;
+import bytecode.visitor.ClassVisitor;
+import bytecode.visitor.ProgramVisitor;
 import java.io.File;
 import org.objectweb.asm.ClassWriter;
 import org.objectweb.asm.Opcodes;
@@ -11,12 +14,14 @@ import org.objectweb.asm.Opcodes;
 import java.io.FileOutputStream;
 import java.io.IOException;
 
-public class ClassCodeGen {
-    public void generateClassCode(ClassNode classNode) {
+public class ClassCodeGen implements ClassVisitor {
+
+    @Override
+    public void visit(ClassNode classNode) {
         ClassWriter classWriter = new ClassWriter(ClassWriter.COMPUTE_FRAMES | ClassWriter.COMPUTE_MAXS);
         Mapper mapper = new Mapper();
         classWriter.visit(Opcodes.V1_8, mapper.mapAccesTypeToOpcode(classNode.accessType), classNode.name, null,
-                "java/lang/Object", null);
+            "java/lang/Object", null);
 
         for (MemberNode memberNode : classNode.members) {
             if (memberNode instanceof FieldNode) {

src/main/java/bytecode/visitor/ClassVisitor.java

@@ -0,0 +1,7 @@
+package bytecode.visitor;
+
+import ast.ClassNode;
+
+public interface ClassVisitor {
+  void visit(ClassNode classNode);
+}

src/main/java/bytecode/visitor/ProgramVisitor.java

@@ -0,0 +1,7 @@
+package bytecode.visitor;
+
+import ast.ProgramNode;
+
+public interface ProgramVisitor {
+  void visit(ProgramNode programNode);
+}

src/main/java/bytecode/visitor/Visitable.java

@@ -0,0 +1,11 @@
+package bytecode.visitor;
+
+public interface Visitable {
+
+  default void accept(ProgramVisitor programVisitor) {
+
+  }
+  default void accept(ClassVisitor classVisitor) {
+
+  }
+}