diff --git a/src/main/java/j2html/TagCreator.java b/src/main/java/j2html/TagCreator.java
index b46e630..eb2dabd 100644
--- a/src/main/java/j2html/TagCreator.java
+++ b/src/main/java/j2html/TagCreator.java
@@ -6,6 +6,8 @@ import java.util.function.*;
 import java.util.stream.*;
 
 public class TagCreator {
+    
+    private TagCreator() {}
 
     /**
      * Creates a DomContent object containing HTML using a mapping function on a collection
diff --git a/src/main/java/j2html/attributes/Attr.java b/src/main/java/j2html/attributes/Attr.java
index e22a78d..c313531 100644
--- a/src/main/java/j2html/attributes/Attr.java
+++ b/src/main/java/j2html/attributes/Attr.java
@@ -1,6 +1,9 @@
 package j2html.attributes;
 
 public class Attr {
+    
+    private Attr() {}
+    
     public static String HIDDEN = "hidden";
     public static String HIGH = "high";
     public static String HREF = "href";
diff --git a/src/main/java/j2html/utils/CSSMin.java b/src/main/java/j2html/utils/CSSMin.java
index 73b04cf..64578cf 100644
--- a/src/main/java/j2html/utils/CSSMin.java
+++ b/src/main/java/j2html/utils/CSSMin.java
@@ -59,6 +59,8 @@ import java.util.logging.*;
 import java.util.regex.*;
 
 public class CSSMin {
+    
+    private CSSMin() {}
 
     private static final Logger LOG = Logger.getLogger(CSSMin.class.getName());
 
diff --git a/src/main/java/j2html/utils/JSMin.java b/src/main/java/j2html/utils/JSMin.java
index 17e804b..3b1c088 100644
--- a/src/main/java/j2html/utils/JSMin.java
+++ b/src/main/java/j2html/utils/JSMin.java
@@ -4,6 +4,8 @@ import com.google.javascript.jscomp.*;
 import com.google.javascript.jscomp.Compiler;
 
 public class JSMin {
+    
+    private JSMin() {}
 
     public static String compressJs(String code, String sourcePath) {
         com.google.javascript.jscomp.Compiler compiler = new Compiler();