diff --git a/config/checkstyle/checkstyle.xml b/config/checkstyle/checkstyle.xml
index 0ed053fc..c7321df1 100644
--- a/config/checkstyle/checkstyle.xml
+++ b/config/checkstyle/checkstyle.xml
@@ -50,7 +50,9 @@
 
     <!-- Checks whether files end with a new line.                        -->
     <!-- See https://checkstyle.org/config_misc.html#NewlineAtEndOfFile -->
-    <module name="NewlineAtEndOfFile"/>
+    <module name="NewlineAtEndOfFile">
+        <property name="lineSeparator" value="lf" />
+    </module>
 
     <!-- Checks that property files contain the same keys.         -->
     <!-- See https://checkstyle.org/config_misc.html#Translation -->
diff --git a/src/main/java/org/hyperskill/hstest/common/JsonUtils.java b/src/main/java/org/hyperskill/hstest/common/JsonUtils.java
index 197f5877..aaf1121a 100644
--- a/src/main/java/org/hyperskill/hstest/common/JsonUtils.java
+++ b/src/main/java/org/hyperskill/hstest/common/JsonUtils.java
@@ -6,7 +6,7 @@
 import com.google.gson.JsonParser;
 import com.google.gson.JsonPrimitive;
 
-public class JsonUtils {
+public final class JsonUtils {
 
     private JsonUtils() { }
 
diff --git a/src/main/java/org/hyperskill/hstest/common/ReflectionUtils.java b/src/main/java/org/hyperskill/hstest/common/ReflectionUtils.java
index 9f331dab..f1426f5f 100644
--- a/src/main/java/org/hyperskill/hstest/common/ReflectionUtils.java
+++ b/src/main/java/org/hyperskill/hstest/common/ReflectionUtils.java
@@ -7,7 +7,8 @@
 
 public final class ReflectionUtils {
 
-    private ReflectionUtils() { }
+    private ReflectionUtils() {
+    }
 
     public static Method getMainMethod(Class<?> clazz) {
         Method mainMethod;
diff --git a/src/main/java/org/hyperskill/hstest/dynamic/SystemHandler.java b/src/main/java/org/hyperskill/hstest/dynamic/SystemHandler.java
index 4692b3da..95f7af37 100644
--- a/src/main/java/org/hyperskill/hstest/dynamic/SystemHandler.java
+++ b/src/main/java/org/hyperskill/hstest/dynamic/SystemHandler.java
@@ -15,7 +15,7 @@ private SystemHandler() { }
     private static Locale oldLocale;
     private static String oldLineSeparator;
 
-    private final static String separatorProperty = "line.separator";
+    private static final String separatorProperty = "line.separator";
 
     public static void setUpSystem() {
         SystemOutHandler.replaceSystemOut();
diff --git a/src/main/java/org/hyperskill/hstest/dynamic/input/DynamicTesting.java b/src/main/java/org/hyperskill/hstest/dynamic/input/DynamicTesting.java
index bb7183ee..5235d8d5 100644
--- a/src/main/java/org/hyperskill/hstest/dynamic/input/DynamicTesting.java
+++ b/src/main/java/org/hyperskill/hstest/dynamic/input/DynamicTesting.java
@@ -178,8 +178,8 @@ static List<DynamicTesting> searchDynamicTestingMethods(Object obj) {
                     if (!Modifier.isPublic(method.getModifiers())) {
                         String className = method.getDeclaringClass().getSimpleName();
                         String methodName = method.getName();
-                        feedback += " Try to declare method \"" +
-                            className + "." + methodName + "\" as public";
+                        feedback += " Try to declare method \""
+                            + className + "." + methodName + "\" as public";
                     }
                     throw new UnexpectedError(feedback, ex);
                 }
@@ -219,8 +219,8 @@ static List<DynamicTesting> searchDynamicTestingVariables(Object obj) {
                     if (!Modifier.isPublic(field.getModifiers())) {
                         String className = field.getDeclaringClass().getSimpleName();
                         String fieldName = field.getName();
-                        feedback += " Try to declare field \"" +
-                            className + "." + fieldName + "\" as public";
+                        feedback += " Try to declare field \""
+                            + className + "." + fieldName + "\" as public";
                     }
                     throw new UnexpectedError(feedback, ex);
                 } catch (Exception ex) {
diff --git a/src/main/java/org/hyperskill/hstest/stage/SpringTest.java b/src/main/java/org/hyperskill/hstest/stage/SpringTest.java
index 1e873ac8..4d2b318f 100644
--- a/src/main/java/org/hyperskill/hstest/stage/SpringTest.java
+++ b/src/main/java/org/hyperskill/hstest/stage/SpringTest.java
@@ -21,7 +21,10 @@
 import java.util.Map;
 
 import static org.hyperskill.hstest.common.Utils.sleep;
-import static org.hyperskill.hstest.mocks.web.constants.Methods.*;
+import static org.hyperskill.hstest.mocks.web.constants.Methods.DELETE;
+import static org.hyperskill.hstest.mocks.web.constants.Methods.GET;
+import static org.hyperskill.hstest.mocks.web.constants.Methods.POST;
+import static org.hyperskill.hstest.mocks.web.constants.Methods.PUT;
 import static org.hyperskill.hstest.mocks.web.request.HttpRequestExecutor.packUrlParams;
 
 public abstract class SpringTest extends StageTest<Object> {
@@ -86,7 +89,7 @@ private static int detectPort() {
 
                     String line;
                     String toSearch = "server.port";
-                    while((line = bufReader.readLine()) != null) {
+                    while ((line = bufReader.readLine()) != null) {
                         if (line.startsWith(toSearch) && line.contains("=")) {
                             String portNumber = line.substring(line.indexOf("=") + 1).trim();
                             return Integer.parseInt(portNumber);
@@ -123,9 +126,9 @@ public void stopSpring() {
             int status = post("/actuator/shutdown", "").send().getStatusCode();
 
             if (status != 200) {
-                throw new WrongAnswer("Cannot stop Spring application.\n" +
-                    "Please make POST \"/actuator/shutdown\" endpoint accessible without authentication.\n" +
-                    "The endpoint should return status code 200, returned " + status + ".");
+                throw new WrongAnswer("Cannot stop Spring application.\n"
+                    + "Please make POST \"/actuator/shutdown\" endpoint accessible without authentication.\n"
+                    + "The endpoint should return status code 200, returned " + status + ".");
             }
 
             springRunning = false;
diff --git a/src/main/java/org/hyperskill/hstest/testing/ExecutionOptions.java b/src/main/java/org/hyperskill/hstest/testing/ExecutionOptions.java
index fa03a513..daf72236 100644
--- a/src/main/java/org/hyperskill/hstest/testing/ExecutionOptions.java
+++ b/src/main/java/org/hyperskill/hstest/testing/ExecutionOptions.java
@@ -3,7 +3,9 @@
 /**
  * Command-line options passed to the JVM listed in one place
  */
-public class ExecutionOptions {
+public final class ExecutionOptions {
+    private ExecutionOptions() { }
+
     /**
      * Unit tests contain slow tests (time limit tests)
      * and to skip them an argument "-DskipSlow=true" should be passed
diff --git a/src/main/java/org/hyperskill/hstest/testing/TestedProgram.java b/src/main/java/org/hyperskill/hstest/testing/TestedProgram.java
index 70d27063..5ff55553 100644
--- a/src/main/java/org/hyperskill/hstest/testing/TestedProgram.java
+++ b/src/main/java/org/hyperskill/hstest/testing/TestedProgram.java
@@ -114,8 +114,8 @@ public TestedProgram(Class<?> testedClass) {
     private String waitOutput(String input) {
         if (!isWaitingInput()) {
             throw new UnexpectedError(
-                "Tested program is not waiting for the input " +
-                "(state == \"" + machine.getState() + "\")");
+                "Tested program is not waiting for the input "
+                    + "(state == \"" + machine.getState() + "\")");
         }
 
         if (noMoreInput) {
@@ -149,7 +149,7 @@ private String waitInput() {
     private void invokeMain(String[] args) {
         try {
             machine.waitState(ProgramState.RUNNING);
-            methodToInvoke.invoke(null, new Object[] { args });
+            methodToInvoke.invoke(null, new Object[] {args});
             machine.setState(ProgramState.FINISHED);
         } catch (InvocationTargetException ex) {
             if (StageTest.getCurrTestRun().getErrorInTest() == null) {
diff --git a/src/main/java/org/hyperskill/hstest/testing/expect/json/ExpectationJsonBuilder.java b/src/main/java/org/hyperskill/hstest/testing/expect/json/ExpectationJsonBuilder.java
index e5ce80e3..d13ecb9e 100644
--- a/src/main/java/org/hyperskill/hstest/testing/expect/json/ExpectationJsonBuilder.java
+++ b/src/main/java/org/hyperskill/hstest/testing/expect/json/ExpectationJsonBuilder.java
@@ -81,7 +81,7 @@ public ExpectationJsonBuilder<T> atPath(String... path) {
                 JsonObject obj = elem.getAsJsonObject();
 
                 if (!obj.has(key)) {
-                    feedback += "\n\nJSON should contain an object with key \""+ key + "\"";
+                    feedback += "\n\nJSON should contain an object with key \"" + key + "\"";
 
                     if (key.matches("[0-9]+")) {
                         int index = Integer.parseInt(key);
diff --git a/src/main/java/org/hyperskill/hstest/testing/expect/json/JsonChecker.java b/src/main/java/org/hyperskill/hstest/testing/expect/json/JsonChecker.java
index 9723c5e1..e16f108c 100644
--- a/src/main/java/org/hyperskill/hstest/testing/expect/json/JsonChecker.java
+++ b/src/main/java/org/hyperskill/hstest/testing/expect/json/JsonChecker.java
@@ -19,7 +19,7 @@
 
 import java.util.regex.Pattern;
 
-public class JsonChecker {
+public final class JsonChecker {
     private JsonChecker() { }
 
     public static JsonAnyBuilder any() {
diff --git a/src/main/java/org/hyperskill/hstest/testing/expect/text/ExpectationTextSearcher.java b/src/main/java/org/hyperskill/hstest/testing/expect/text/ExpectationTextSearcher.java
index 1e06f80a..d2267b1c 100644
--- a/src/main/java/org/hyperskill/hstest/testing/expect/text/ExpectationTextSearcher.java
+++ b/src/main/java/org/hyperskill/hstest/testing/expect/text/ExpectationTextSearcher.java
@@ -80,7 +80,7 @@ public List<Double> doublesOnly(String delim) {
     }
 
     public List<String> regex(String pattern) {
-        return regex(pattern,"words with pattern " + pattern);
+        return regex(pattern, "words with pattern " + pattern);
     }
 
     public List<String> regex(String pattern, String patternDescription) {