diff --git a/src/main/java/cz/cvut/fel/sit/omo/foodchain/FoodChain.java b/src/main/java/cz/cvut/fel/sit/omo/foodchain/FoodChain.java
index 353b7dd..585f276 100644
--- a/src/main/java/cz/cvut/fel/sit/omo/foodchain/FoodChain.java
+++ b/src/main/java/cz/cvut/fel/sit/omo/foodchain/FoodChain.java
@@ -1,4 +1,7 @@
 package cz.cvut.fel.sit.omo.foodchain;
 
 public class FoodChain {
+    public static void main(String[] args) {
+
+    }
 }
diff --git a/src/main/java/cz/cvut/fel/sit/omo/foodchain/channel/Channel.java b/src/main/java/cz/cvut/fel/sit/omo/foodchain/channel/Channel.java
deleted file mode 100644
index 81487d5..0000000
--- a/src/main/java/cz/cvut/fel/sit/omo/foodchain/channel/Channel.java
+++ /dev/null
@@ -1,4 +0,0 @@
-package cz.cvut.fel.sit.omo.foodchain.channel;
-
-public interface Channel {
-}
diff --git a/src/main/java/cz/cvut/fel/sit/omo/foodchain/channel/ChannelBase.java b/src/main/java/cz/cvut/fel/sit/omo/foodchain/channel/ChannelBase.java
index 4a63d69..5ca051c 100644
--- a/src/main/java/cz/cvut/fel/sit/omo/foodchain/channel/ChannelBase.java
+++ b/src/main/java/cz/cvut/fel/sit/omo/foodchain/channel/ChannelBase.java
@@ -1,4 +1,11 @@
 package cz.cvut.fel.sit.omo.foodchain.channel;
 
-public abstract class ChannelBase implements Channel {
+import cz.cvut.fel.sit.omo.foodchain.operation.Transaction;
+import cz.cvut.fel.sit.omo.foodchain.requirement.Requirement;
+
+import java.util.Queue;
+
+public abstract class ChannelBase implements IChannel {
+    Queue<Requirement> requirements;
+    Queue<Transaction> transactions;
 }
diff --git a/src/main/java/cz/cvut/fel/sit/omo/foodchain/channel/FruitChannel.java b/src/main/java/cz/cvut/fel/sit/omo/foodchain/channel/FruitChannel.java
index 2084591..50d4bcd 100644
--- a/src/main/java/cz/cvut/fel/sit/omo/foodchain/channel/FruitChannel.java
+++ b/src/main/java/cz/cvut/fel/sit/omo/foodchain/channel/FruitChannel.java
@@ -1,4 +1,26 @@
 package cz.cvut.fel.sit.omo.foodchain.channel;
 
+import cz.cvut.fel.sit.omo.foodchain.operation.Transaction;
+import cz.cvut.fel.sit.omo.foodchain.requirement.Requirement;
+
 public class FruitChannel extends ChannelBase {
+    @Override
+    public Transaction getNextTransaction() {
+        return null;
+    }
+
+    @Override
+    public Requirement getNextRequirement() {
+        return null;
+    }
+
+    @Override
+    public void addRequirement(Requirement requirement) {
+
+    }
+
+    @Override
+    public void addTransaction(Transaction transaction) {
+
+    }
 }
diff --git a/src/main/java/cz/cvut/fel/sit/omo/foodchain/channel/IChannel.java b/src/main/java/cz/cvut/fel/sit/omo/foodchain/channel/IChannel.java
new file mode 100644
index 0000000..e4403c8
--- /dev/null
+++ b/src/main/java/cz/cvut/fel/sit/omo/foodchain/channel/IChannel.java
@@ -0,0 +1,12 @@
+package cz.cvut.fel.sit.omo.foodchain.channel;
+
+import cz.cvut.fel.sit.omo.foodchain.operation.Transaction;
+import cz.cvut.fel.sit.omo.foodchain.requirement.Requirement;
+
+public interface IChannel {
+    public Transaction getNextTransaction();
+    public Requirement getNextRequirement();
+
+    public void addRequirement(Requirement requirement);
+    public void addTransaction(Transaction transaction);
+}
diff --git a/src/main/java/cz/cvut/fel/sit/omo/foodchain/channel/MeetChannel.java b/src/main/java/cz/cvut/fel/sit/omo/foodchain/channel/MeetChannel.java
index e02fe24..fae4a81 100644
--- a/src/main/java/cz/cvut/fel/sit/omo/foodchain/channel/MeetChannel.java
+++ b/src/main/java/cz/cvut/fel/sit/omo/foodchain/channel/MeetChannel.java
@@ -1,4 +1,26 @@
 package cz.cvut.fel.sit.omo.foodchain.channel;
 
+import cz.cvut.fel.sit.omo.foodchain.operation.Transaction;
+import cz.cvut.fel.sit.omo.foodchain.requirement.Requirement;
+
 public class MeetChannel extends ChannelBase {
+    @Override
+    public Transaction getNextTransaction() {
+        return null;
+    }
+
+    @Override
+    public Requirement getNextRequirement() {
+        return null;
+    }
+
+    @Override
+    public void addRequirement(Requirement requirement) {
+
+    }
+
+    @Override
+    public void addTransaction(Transaction transaction) {
+
+    }
 }
diff --git a/src/main/java/cz/cvut/fel/sit/omo/foodchain/channel/VegetableChannel.java b/src/main/java/cz/cvut/fel/sit/omo/foodchain/channel/VegetableChannel.java
index 0b455d0..0a68c83 100644
--- a/src/main/java/cz/cvut/fel/sit/omo/foodchain/channel/VegetableChannel.java
+++ b/src/main/java/cz/cvut/fel/sit/omo/foodchain/channel/VegetableChannel.java
@@ -1,4 +1,26 @@
 package cz.cvut.fel.sit.omo.foodchain.channel;
 
+import cz.cvut.fel.sit.omo.foodchain.operation.Transaction;
+import cz.cvut.fel.sit.omo.foodchain.requirement.Requirement;
+
 public class VegetableChannel extends ChannelBase {
+    @Override
+    public Transaction getNextTransaction() {
+        return null;
+    }
+
+    @Override
+    public Requirement getNextRequirement() {
+        return null;
+    }
+
+    @Override
+    public void addRequirement(Requirement requirement) {
+
+    }
+
+    @Override
+    public void addTransaction(Transaction transaction) {
+
+    }
 }
diff --git a/src/main/java/cz/cvut/fel/sit/omo/foodchain/node/BuyerNodeBase.java b/src/main/java/cz/cvut/fel/sit/omo/foodchain/node/BuyerNodeBase.java
index 3ed8d45..91caca6 100644
--- a/src/main/java/cz/cvut/fel/sit/omo/foodchain/node/BuyerNodeBase.java
+++ b/src/main/java/cz/cvut/fel/sit/omo/foodchain/node/BuyerNodeBase.java
@@ -2,7 +2,7 @@ package cz.cvut.fel.sit.omo.foodchain.node;
 
 import cz.cvut.fel.sit.omo.foodchain.product.Product;
 
-public class BuyerNodeBase extends NodeBase implements BuyerNodeInterface {
+public class BuyerNodeBase extends NodeBase implements IBuyerNode {
     @Override
     public void sellProduct(Product product) {
 
diff --git a/src/main/java/cz/cvut/fel/sit/omo/foodchain/node/BuyerNodeInterface.java b/src/main/java/cz/cvut/fel/sit/omo/foodchain/node/IBuyerNode.java
similarity index 82%
rename from src/main/java/cz/cvut/fel/sit/omo/foodchain/node/BuyerNodeInterface.java
rename to src/main/java/cz/cvut/fel/sit/omo/foodchain/node/IBuyerNode.java
index 47faf95..cc8f592 100644
--- a/src/main/java/cz/cvut/fel/sit/omo/foodchain/node/BuyerNodeInterface.java
+++ b/src/main/java/cz/cvut/fel/sit/omo/foodchain/node/IBuyerNode.java
@@ -2,7 +2,7 @@ package cz.cvut.fel.sit.omo.foodchain.node;
 
 import cz.cvut.fel.sit.omo.foodchain.product.Product;
 
-public interface BuyerNodeInterface {
+public interface IBuyerNode {
 
     void sellProduct(Product product);
 
diff --git a/src/main/java/cz/cvut/fel/sit/omo/foodchain/node/NodeInterface.java b/src/main/java/cz/cvut/fel/sit/omo/foodchain/node/INode.java
similarity index 72%
rename from src/main/java/cz/cvut/fel/sit/omo/foodchain/node/NodeInterface.java
rename to src/main/java/cz/cvut/fel/sit/omo/foodchain/node/INode.java
index 3ea748a..7ef03d5 100644
--- a/src/main/java/cz/cvut/fel/sit/omo/foodchain/node/NodeInterface.java
+++ b/src/main/java/cz/cvut/fel/sit/omo/foodchain/node/INode.java
@@ -1,6 +1,6 @@
 package cz.cvut.fel.sit.omo.foodchain.node;
 
-import cz.cvut.fel.sit.omo.foodchain.channel.Channel;
+import cz.cvut.fel.sit.omo.foodchain.channel.IChannel;
 import cz.cvut.fel.sit.omo.foodchain.operation.Action;
 import cz.cvut.fel.sit.omo.foodchain.operation.Transaction;
 import cz.cvut.fel.sit.omo.foodchain.product.Product;
@@ -10,22 +10,22 @@ import cz.cvut.fel.sit.omo.foodchain.signature.Signature;
 
 import java.awt.*;
 
-public interface NodeInterface {
-    void sendTransaction(Product product, NodeInterface node);
+public interface INode {
+    void sendTransaction(Product product, INode INode);
 
     void receiveTransaction(Transaction transaction);
 
     void refuseTransaction(Transaction transaction);
 
-    Transaction readNextTransaction(Channel channel);
+    Transaction readNextTransaction(IChannel channel);
 
-    Requirement readNextRequirement(Channel channel);
+    Requirement readNextRequirement(IChannel channel);
 
     void acceptRequirement(Requirement requirement);
 
-    void subscribeToChannel(Channel channel);
+    void subscribeToChannel(IChannel channel);
 
-    void unsubscribeFromChannel(Channel channel);
+    void unsubscribeFromChannel(IChannel channel);
 
     void doAction(Action action, Product product);
 
diff --git a/src/main/java/cz/cvut/fel/sit/omo/foodchain/node/SellerNodeInterface.java b/src/main/java/cz/cvut/fel/sit/omo/foodchain/node/ISellerNode.java
similarity index 78%
rename from src/main/java/cz/cvut/fel/sit/omo/foodchain/node/SellerNodeInterface.java
rename to src/main/java/cz/cvut/fel/sit/omo/foodchain/node/ISellerNode.java
index ed785bc..1f0c21e 100644
--- a/src/main/java/cz/cvut/fel/sit/omo/foodchain/node/SellerNodeInterface.java
+++ b/src/main/java/cz/cvut/fel/sit/omo/foodchain/node/ISellerNode.java
@@ -2,7 +2,7 @@ package cz.cvut.fel.sit.omo.foodchain.node;
 
 import cz.cvut.fel.sit.omo.foodchain.product.Product;
 
-public interface SellerNodeInterface {
+public interface ISellerNode {
 
     void buyProduct(Product product);
 }
diff --git a/src/main/java/cz/cvut/fel/sit/omo/foodchain/node/NodeBase.java b/src/main/java/cz/cvut/fel/sit/omo/foodchain/node/NodeBase.java
index b5af499..2c6e46a 100644
--- a/src/main/java/cz/cvut/fel/sit/omo/foodchain/node/NodeBase.java
+++ b/src/main/java/cz/cvut/fel/sit/omo/foodchain/node/NodeBase.java
@@ -1,6 +1,6 @@
 package cz.cvut.fel.sit.omo.foodchain.node;
 
-import cz.cvut.fel.sit.omo.foodchain.channel.Channel;
+import cz.cvut.fel.sit.omo.foodchain.channel.IChannel;
 import cz.cvut.fel.sit.omo.foodchain.operation.Action;
 import cz.cvut.fel.sit.omo.foodchain.operation.Transaction;
 import cz.cvut.fel.sit.omo.foodchain.product.Product;
@@ -10,9 +10,9 @@ import cz.cvut.fel.sit.omo.foodchain.signature.Signature;
 
 import java.awt.*;
 
-public class NodeBase implements NodeInterface {
+public class NodeBase implements INode {
     @Override
-    public void sendTransaction(Product product, NodeInterface node) {
+    public void sendTransaction(Product product, INode node) {
 
     }
 
@@ -27,12 +27,12 @@ public class NodeBase implements NodeInterface {
     }
 
     @Override
-    public Transaction readNextTransaction(Channel channel) {
+    public Transaction readNextTransaction(IChannel channel) {
         return null;
     }
 
     @Override
-    public Requirement readNextRequirement(Channel channel) {
+    public Requirement readNextRequirement(IChannel channel) {
         return null;
     }
 
@@ -42,12 +42,12 @@ public class NodeBase implements NodeInterface {
     }
 
     @Override
-    public void subscribeToChannel(Channel channel) {
+    public void subscribeToChannel(IChannel channel) {
 
     }
 
     @Override
-    public void unsubscribeFromChannel(Channel channel) {
+    public void unsubscribeFromChannel(IChannel channel) {
 
     }
 
diff --git a/src/main/java/cz/cvut/fel/sit/omo/foodchain/node/RetailerNodeBase.java b/src/main/java/cz/cvut/fel/sit/omo/foodchain/node/RetailerNodeBase.java
index 61ab580..3081dec 100644
--- a/src/main/java/cz/cvut/fel/sit/omo/foodchain/node/RetailerNodeBase.java
+++ b/src/main/java/cz/cvut/fel/sit/omo/foodchain/node/RetailerNodeBase.java
@@ -2,7 +2,7 @@ package cz.cvut.fel.sit.omo.foodchain.node;
 
 import cz.cvut.fel.sit.omo.foodchain.product.Product;
 
-public class RetailerNodeBase extends NodeBase implements BuyerNodeInterface, SellerNodeInterface {
+public class RetailerNodeBase extends NodeBase implements IBuyerNode, ISellerNode {
     @Override
     public void sellProduct(Product product) {
 
diff --git a/src/main/java/cz/cvut/fel/sit/omo/foodchain/node/SellerNodeBase.java b/src/main/java/cz/cvut/fel/sit/omo/foodchain/node/SellerNodeBase.java
index c58052c..59abda2 100644
--- a/src/main/java/cz/cvut/fel/sit/omo/foodchain/node/SellerNodeBase.java
+++ b/src/main/java/cz/cvut/fel/sit/omo/foodchain/node/SellerNodeBase.java
@@ -2,7 +2,7 @@ package cz.cvut.fel.sit.omo.foodchain.node;
 
 import cz.cvut.fel.sit.omo.foodchain.product.Product;
 
-public class SellerNodeBase extends NodeBase implements SellerNodeInterface {
+public class SellerNodeBase extends NodeBase implements ISellerNode {
     @Override
     public void buyProduct(Product product) {
 
diff --git a/src/main/java/cz/cvut/fel/sit/omo/foodchain/operation/OperationInterface.java b/src/main/java/cz/cvut/fel/sit/omo/foodchain/operation/IOperation.java
similarity index 57%
rename from src/main/java/cz/cvut/fel/sit/omo/foodchain/operation/OperationInterface.java
rename to src/main/java/cz/cvut/fel/sit/omo/foodchain/operation/IOperation.java
index 70ac9ec..9abe7d6 100644
--- a/src/main/java/cz/cvut/fel/sit/omo/foodchain/operation/OperationInterface.java
+++ b/src/main/java/cz/cvut/fel/sit/omo/foodchain/operation/IOperation.java
@@ -1,4 +1,4 @@
 package cz.cvut.fel.sit.omo.foodchain.operation;
 
-public interface OperationInterface {
+public interface IOperation {
 }
diff --git a/src/main/java/cz/cvut/fel/sit/omo/foodchain/operation/OperationBase.java b/src/main/java/cz/cvut/fel/sit/omo/foodchain/operation/OperationBase.java
index 36107d1..6e9403b 100644
--- a/src/main/java/cz/cvut/fel/sit/omo/foodchain/operation/OperationBase.java
+++ b/src/main/java/cz/cvut/fel/sit/omo/foodchain/operation/OperationBase.java
@@ -1,4 +1,5 @@
 package cz.cvut.fel.sit.omo.foodchain.operation;
 
 public class OperationBase {
+    IOperation lastOperation;
 }
diff --git a/src/main/java/cz/cvut/fel/sit/omo/foodchain/pool/ChannelPool.java b/src/main/java/cz/cvut/fel/sit/omo/foodchain/pool/ChannelPool.java
index 35df01a..8419126 100644
--- a/src/main/java/cz/cvut/fel/sit/omo/foodchain/pool/ChannelPool.java
+++ b/src/main/java/cz/cvut/fel/sit/omo/foodchain/pool/ChannelPool.java
@@ -1,6 +1,6 @@
 package cz.cvut.fel.sit.omo.foodchain.pool;
 
-import cz.cvut.fel.sit.omo.foodchain.channel.Channel;
+import cz.cvut.fel.sit.omo.foodchain.channel.IChannel;
 
-public class ChannelPool extends PoolListBase<Channel> {
+public class ChannelPool extends PoolListBase<IChannel> {
 }
diff --git a/src/main/java/cz/cvut/fel/sit/omo/foodchain/pool/PoolInterface.java b/src/main/java/cz/cvut/fel/sit/omo/foodchain/pool/IPool.java
similarity index 85%
rename from src/main/java/cz/cvut/fel/sit/omo/foodchain/pool/PoolInterface.java
rename to src/main/java/cz/cvut/fel/sit/omo/foodchain/pool/IPool.java
index b02beb2..e91f2bf 100644
--- a/src/main/java/cz/cvut/fel/sit/omo/foodchain/pool/PoolInterface.java
+++ b/src/main/java/cz/cvut/fel/sit/omo/foodchain/pool/IPool.java
@@ -2,7 +2,7 @@ package cz.cvut.fel.sit.omo.foodchain.pool;
 
 import java.util.Collection;
 
-public interface PoolInterface<T> {
+public interface IPool<T> {
     Collection<T> findAll();
 
     void add(T element);
diff --git a/src/main/java/cz/cvut/fel/sit/omo/foodchain/pool/NodePool.java b/src/main/java/cz/cvut/fel/sit/omo/foodchain/pool/NodePool.java
index 65594d1..b66bbce 100644
--- a/src/main/java/cz/cvut/fel/sit/omo/foodchain/pool/NodePool.java
+++ b/src/main/java/cz/cvut/fel/sit/omo/foodchain/pool/NodePool.java
@@ -1,6 +1,6 @@
 package cz.cvut.fel.sit.omo.foodchain.pool;
 
-import cz.cvut.fel.sit.omo.foodchain.node.NodeInterface;
+import cz.cvut.fel.sit.omo.foodchain.node.INode;
 
-public class NodePool extends PoolListBase<NodeInterface> {
+public class NodePool extends PoolListBase<INode> {
 }
diff --git a/src/main/java/cz/cvut/fel/sit/omo/foodchain/pool/PoolListBase.java b/src/main/java/cz/cvut/fel/sit/omo/foodchain/pool/PoolListBase.java
index 8e41666..48f9ce8 100644
--- a/src/main/java/cz/cvut/fel/sit/omo/foodchain/pool/PoolListBase.java
+++ b/src/main/java/cz/cvut/fel/sit/omo/foodchain/pool/PoolListBase.java
@@ -4,7 +4,7 @@ import java.util.Collection;
 import java.util.LinkedList;
 import java.util.List;
 
-public abstract class PoolListBase<T> implements PoolInterface<T> {
+public abstract class PoolListBase<T> implements IPool<T> {
     List<T> pool;
 
     public PoolListBase() {
diff --git a/src/main/java/cz/cvut/fel/sit/omo/foodchain/product/ProductState.java b/src/main/java/cz/cvut/fel/sit/omo/foodchain/product/ProductState.java
index 0f557c9..90518fb 100644
--- a/src/main/java/cz/cvut/fel/sit/omo/foodchain/product/ProductState.java
+++ b/src/main/java/cz/cvut/fel/sit/omo/foodchain/product/ProductState.java
@@ -1,4 +1,4 @@
 package cz.cvut.fel.sit.omo.foodchain.product;
 
-public class ProductState {
+public enum ProductState {
 }
diff --git a/src/main/java/cz/cvut/fel/sit/omo/foodchain/reporting/ReportTextFileVisitor.java b/src/main/java/cz/cvut/fel/sit/omo/foodchain/reporting/ReportTextFileVisitor.java
index d03e08b..c18d209 100644
--- a/src/main/java/cz/cvut/fel/sit/omo/foodchain/reporting/ReportTextFileVisitor.java
+++ b/src/main/java/cz/cvut/fel/sit/omo/foodchain/reporting/ReportTextFileVisitor.java
@@ -1,4 +1,19 @@
 package cz.cvut.fel.sit.omo.foodchain.reporting;
 
+import cz.cvut.fel.sit.omo.foodchain.channel.IChannel;
+import cz.cvut.fel.sit.omo.foodchain.node.INode;
+import cz.cvut.fel.sit.omo.foodchain.operation.IOperation;
+
 public class ReportTextFileVisitor {
+    public void visit(INode node){
+
+    }
+
+    public void visit(IOperation operationBase){
+
+    }
+
+    public void visit(IChannel channel){
+
+    }
 }
diff --git a/src/main/java/cz/cvut/fel/sit/omo/foodchain/util/Singleton.java b/src/main/java/cz/cvut/fel/sit/omo/foodchain/util/Singleton.java
index 9954da5..cf27b45 100644
--- a/src/main/java/cz/cvut/fel/sit/omo/foodchain/util/Singleton.java
+++ b/src/main/java/cz/cvut/fel/sit/omo/foodchain/util/Singleton.java
@@ -10,7 +10,7 @@ public class Singleton {
     private static final Singleton instance = new Singleton();
 
     @SuppressWarnings("rawtypes")
-    private final Map<Class, Object> mapHolder = new HashMap<Class, Object>();
+    private final Map<Class, Object> mapHolder = new HashMap<>();
 
     private Singleton() {
     }