diff --git a/eu.heili/DigitalInput.java b/eu.heili/DigitalInput.java
index a7ff6c0..c428309 100644
--- a/eu.heili/DigitalInput.java
+++ b/eu.heili/DigitalInput.java
@@ -5,7 +5,7 @@ public class DigitalInput {
         setValue(value);
     }
 
-    public DigitalInput(LogicGate gate) {
+    public DigitalInput(final LogicGate gate) {
         setValue(gate);
     }
 
diff --git a/eu.heili/EnxorGate.java b/eu.heili/EnxorGate.java
index 5f78be3..87bb5a2 100644
--- a/eu.heili/EnxorGate.java
+++ b/eu.heili/EnxorGate.java
@@ -1,9 +1,9 @@
 public class EnxorGate extends ExorGate {
-    public EnxorGate(int inputnr) {
+    public EnxorGate(final int inputnr) {
         super(inputnr);
     }
 
-    public EnxorGate(DigitalInput... inputvals) {
+    public EnxorGate(final DigitalInput... inputvals) {
         super(inputvals);
     }
 
diff --git a/eu.heili/ExorGate.java b/eu.heili/ExorGate.java
index 2757b8a..bdb3929 100644
--- a/eu.heili/ExorGate.java
+++ b/eu.heili/ExorGate.java
@@ -1,11 +1,11 @@
 public class ExorGate extends LogicGate {
-    public ExorGate(int inputnr) {
+    public ExorGate(final int inputnr) {
         super(inputnr);
         if (inputnr > 2)
             throw (new TooManyInputsException());
     }
 
-    public ExorGate(DigitalInput... inputvals) {
+    public ExorGate(final DigitalInput... inputvals) {
         super(inputvals);
         if (inputvals.length > 2)
             throw (new TooManyInputsException());
diff --git a/eu.heili/Main.java b/eu.heili/Main.java
index 8881345..31b6450 100644
--- a/eu.heili/Main.java
+++ b/eu.heili/Main.java
@@ -35,8 +35,8 @@ public class Main {
 
         /** bsp 1 **/
 
-        boolean x = false;
-        boolean y = true;
+        final boolean x = false;
+        final boolean y = true;
 
         LogicGate s = new OrGate(
                 new DigitalInput(new AndGate(
@@ -62,8 +62,8 @@ public class Main {
         System.out.println("output of s: " + s.getOutput());
 
         /** bsp. 2 **/
-        boolean xx = true;
-        boolean yy = false;
+        final boolean xx = true;
+        final boolean yy = false;
 
         LogicGate ss = new ExorGate(
                 new DigitalInput(xx),
diff --git a/eu.heili/NandGate.java b/eu.heili/NandGate.java
index d6143b2..3764c7d 100644
--- a/eu.heili/NandGate.java
+++ b/eu.heili/NandGate.java
@@ -1,9 +1,9 @@
 public class NandGate extends AndGate {
-    public NandGate(int inputnr) {
+    public NandGate(final int inputnr) {
         super(inputnr);
     }
 
-    public NandGate(DigitalInput... inputvals) {
+    public NandGate(final DigitalInput... inputvals) {
         super(inputvals);
     }
 
diff --git a/eu.heili/NorGate.java b/eu.heili/NorGate.java
index ce4fccb..b6ad163 100644
--- a/eu.heili/NorGate.java
+++ b/eu.heili/NorGate.java
@@ -1,9 +1,9 @@
 public class NorGate extends OrGate {
-    public NorGate(int inputnr) {
+    public NorGate(final int inputnr) {
         super(inputnr);
     }
 
-    public NorGate(DigitalInput... inputvals) {
+    public NorGate(final DigitalInput... inputvals) {
         super(inputvals);
     }
 
diff --git a/eu.heili/NotGate.java b/eu.heili/NotGate.java
index c77179b..d1ea461 100644
--- a/eu.heili/NotGate.java
+++ b/eu.heili/NotGate.java
@@ -3,7 +3,7 @@ public class NotGate extends LogicGate {
         super(1);
     }
 
-    public NotGate(DigitalInput inputval) {
+    public NotGate(final DigitalInput inputval) {
         super(inputval);
     }