diff --git a/src/main/java/Example.java b/src/main/java/Example.txt
similarity index 70%
rename from src/main/java/Example.java
rename to src/main/java/Example.txt
index 6657954..8c28495 100644
--- a/src/main/java/Example.java
+++ b/src/main/java/Example.txt
@@ -1,6 +1,7 @@
 class Example {
 
     int test;
+    char test;
 
 }
 
diff --git a/src/main/java/Main.java b/src/main/java/Main.java
index 258411a..165c82d 100644
--- a/src/main/java/Main.java
+++ b/src/main/java/Main.java
@@ -9,9 +9,6 @@ import parser.ASTBuilder;
 import parser.generated.SimpleJavaLexer;
 import parser.generated.SimpleJavaParser;
 import semantic.SemanticAnalyzer;
-import ast.ClassNode;
-import ast.ProgramNode;
-import bytecode.ByteCodeGenerator;
 
 import java.io.IOException;
 import java.nio.file.Paths;
@@ -20,7 +17,7 @@ public class Main {
     public static void main(String[] args) throws Exception {
         CharStream codeCharStream = null;
         try {
-            codeCharStream = CharStreams.fromPath(Paths.get("./Example.java"));
+            codeCharStream = CharStreams.fromPath(Paths.get("src/main/java/Example.txt"));
             parsefile(codeCharStream);
         } catch (IOException e) {
             System.err.println("Error reading the file: " + e.getMessage());
@@ -42,7 +39,7 @@ public class Main {
         // Optionally print or process the AST
         System.out.println("Parsed " + ast.classes.size() + " classes with identifiers/names:");
         for (ClassNode classNode : ast.classes) {
-            System.out.println(classNode.name);
+            System.out.println(classNode.identifier.getName());
         }
 
         SemanticAnalyzer semanticAnalyzer = new SemanticAnalyzer();
diff --git a/src/main/java/ast/ClassNode.java b/src/main/java/ast/ClassNode.java
index 7943b5a..46a64eb 100644
--- a/src/main/java/ast/ClassNode.java
+++ b/src/main/java/ast/ClassNode.java
@@ -4,7 +4,7 @@ import java.util.ArrayList;
 import java.util.List;
 
 public class ClassNode extends ASTNode{
-    public String name;
+    public Identifier identifier;
     public List<MemberNode> members = new ArrayList<>();
     public boolean hasConstructor = false;
 
@@ -17,7 +17,7 @@ public class ClassNode extends ASTNode{
 
     public void ensureConstructor(){
         if(!hasConstructor) {
-            ConstructorNode constructor = new ConstructorNode(new TypeNode("public"), name);
+            ConstructorNode constructor = new ConstructorNode(new TypeNode("public"), identifier.getName());
             members.add(0,constructor);
         }
     }
diff --git a/src/main/java/ast/FieldNode.java b/src/main/java/ast/FieldNode.java
index 948701f..4d30573 100644
--- a/src/main/java/ast/FieldNode.java
+++ b/src/main/java/ast/FieldNode.java
@@ -2,11 +2,11 @@ package ast;
 
 public class FieldNode extends MemberNode {
     public TypeNode type;
-    public String name;
+    public Identifier identifier;
 
     public FieldNode(TypeNode type, String name){
         this.type = type;
-        this.name = name;
+        this.identifier = new Identifier(name);
     }
 
 }
diff --git a/src/main/java/ast/Identifier.java b/src/main/java/ast/Identifier.java
new file mode 100644
index 0000000..2f6fe73
--- /dev/null
+++ b/src/main/java/ast/Identifier.java
@@ -0,0 +1,27 @@
+package ast;
+
+public class Identifier {
+
+    private String name;
+
+    public Identifier(String name){
+        this.name = name;
+    }
+
+    public String getName(){
+        return name;
+    }
+
+    public boolean equals(Object obj) {
+        if(obj instanceof Identifier){
+            Identifier identifier = (Identifier) obj;
+            if(name.equals(identifier.getName())){
+                return true;
+            } else {
+                return false;
+            }
+        }
+        return super.equals(obj);
+    }
+
+}
diff --git a/src/main/java/ast/MethodNode.java b/src/main/java/ast/MethodNode.java
index b8e15f2..4dd77f4 100644
--- a/src/main/java/ast/MethodNode.java
+++ b/src/main/java/ast/MethodNode.java
@@ -5,7 +5,7 @@ import java.util.List;
 
 public class MethodNode extends MemberNode{
     public TypeNode visibility;
-    public String name;
+    public Identifier identifier;
 
     public ParameterListNode parameters;
 
@@ -14,13 +14,13 @@ public class MethodNode extends MemberNode{
     public MethodNode(TypeNode visibility, String name, ParameterListNode parameters,
                       List<StatementNode> statements){
         this.visibility = visibility;
-        this.name = name;
+        this.identifier = new Identifier(name);
         this.parameters = parameters;
         this.statements = statements;
     }
 
     public MethodNode(TypeNode visibility, String name){
         this.visibility = visibility;
-        this.name = name;
+        this.identifier = new Identifier(name);
     }
 }
diff --git a/src/main/java/bytecode/ClassCodeGen.java b/src/main/java/bytecode/ClassCodeGen.java
index 619068a..7ce5506 100644
--- a/src/main/java/bytecode/ClassCodeGen.java
+++ b/src/main/java/bytecode/ClassCodeGen.java
@@ -10,7 +10,7 @@ import java.io.IOException;
 public class ClassCodeGen {
     public void generateClassCode(ClassNode classNode) {
         ClassWriter classWriter = new ClassWriter(ClassWriter.COMPUTE_FRAMES | ClassWriter.COMPUTE_MAXS);
-        classWriter.visit(Opcodes.V1_8, Opcodes.ACC_PUBLIC, classNode.name, null,
+        classWriter.visit(Opcodes.V1_8, Opcodes.ACC_PUBLIC, classNode.identifier.getName(), null,
                 "java/lang/Object", null);
 
         FieldCodeGen fieldCodeGen = new FieldCodeGen();
@@ -20,7 +20,7 @@ public class ClassCodeGen {
         methodCodeGen.generateMethodCode(classWriter);
 
         classWriter.visitEnd();
-        printIntoClassFile(classWriter.toByteArray(), classNode.name);
+        printIntoClassFile(classWriter.toByteArray(), classNode.identifier.getName());
 
         classWriter.visitEnd();
     }
diff --git a/src/main/java/parser/ASTBuilder.java b/src/main/java/parser/ASTBuilder.java
index 6519cc1..42e3fcd 100644
--- a/src/main/java/parser/ASTBuilder.java
+++ b/src/main/java/parser/ASTBuilder.java
@@ -20,7 +20,7 @@ public class ASTBuilder extends SimpleJavaBaseVisitor<ASTNode> {
     @Override
     public ASTNode visitClassDeclaration(SimpleJavaParser.ClassDeclarationContext ctx) {
         ClassNode classNode = new ClassNode();
-        classNode.name = ctx.IDENTIFIER().getText();
+        classNode.identifier = new Identifier(ctx.IDENTIFIER().getText());
         for (SimpleJavaParser.MemberDeclarationContext member : ctx.memberDeclaration()) {
             classNode.addMember((MemberNode) visit(member));
         }
diff --git a/src/main/java/semantic/SemanticAnalyzer.java b/src/main/java/semantic/SemanticAnalyzer.java
index e486d16..5e405e5 100644
--- a/src/main/java/semantic/SemanticAnalyzer.java
+++ b/src/main/java/semantic/SemanticAnalyzer.java
@@ -3,16 +3,20 @@ package semantic;
 
 import ast.*;
 
+import java.util.ArrayList;
 import java.util.List;
 
 public class SemanticAnalyzer {
+
+    List<Identifier> usedIdentifier = new ArrayList<>();
+
     public void analyze(ASTNode node) {
         if (node == null) return;
 
         if (node instanceof ClassNode) {
 
             ClassNode classNode = (ClassNode) node;
-            if(classNode.name == null){
+            if(classNode.identifier == null){
                 System.out.println("Klasse besitzt keinen Identifier");
             }
 
@@ -24,6 +28,14 @@ public class SemanticAnalyzer {
 
         }else if (node instanceof ConstructorNode) {
 
+        }else if (node instanceof FieldNode) {
+
+            FieldNode fieldNode = (FieldNode) node;
+            if(identifierAlreadyUsed(fieldNode.identifier)){
+                throw new RuntimeException("Error: Identifier already used");
+            }
+            usedIdentifier.add(fieldNode.identifier);
+
         }else if (node instanceof ProgramNode) {
             ProgramNode programNode = (ProgramNode) node;
             List<ClassNode> classes = programNode.classes;
@@ -33,4 +45,13 @@ public class SemanticAnalyzer {
         }
 
     }
+
+    public boolean identifierAlreadyUsed(Identifier identifier){
+        if(usedIdentifier.contains(identifier)){
+            return true;
+        } else {
+            return false;
+        }
+    }
+
 }
\ No newline at end of file