diff --git a/code_samples/simple_language_plugin/src/main/java/org/intellij/sdk/language/SimpleBlock.java b/code_samples/simple_language_plugin/src/main/java/org/intellij/sdk/language/SimpleBlock.java
index 04e8ad30a..6d30b51d8 100644
--- a/code_samples/simple_language_plugin/src/main/java/org/intellij/sdk/language/SimpleBlock.java
+++ b/code_samples/simple_language_plugin/src/main/java/org/intellij/sdk/language/SimpleBlock.java
@@ -13,7 +13,7 @@ import java.util.ArrayList;
 import java.util.List;
 
 public class SimpleBlock extends AbstractBlock {
-  private SpacingBuilder spacingBuilder;
+  private final SpacingBuilder spacingBuilder;
   
   protected SimpleBlock(@NotNull ASTNode node, @Nullable Wrap wrap, @Nullable Alignment alignment,
                         SpacingBuilder spacingBuilder) {
diff --git a/code_samples/simple_language_plugin/src/main/java/org/intellij/sdk/language/SimpleCreatePropertyQuickFix.java b/code_samples/simple_language_plugin/src/main/java/org/intellij/sdk/language/SimpleCreatePropertyQuickFix.java
index 8a823d84e..55227c426 100644
--- a/code_samples/simple_language_plugin/src/main/java/org/intellij/sdk/language/SimpleCreatePropertyQuickFix.java
+++ b/code_samples/simple_language_plugin/src/main/java/org/intellij/sdk/language/SimpleCreatePropertyQuickFix.java
@@ -28,7 +28,7 @@ import org.jetbrains.annotations.NotNull;
 import java.util.Collection;
 
 class SimpleCreatePropertyQuickFix extends BaseIntentionAction {
-  private String key;
+  private final String key;
   
   SimpleCreatePropertyQuickFix(String key) {
     this.key = key;
@@ -89,4 +89,4 @@ class SimpleCreatePropertyQuickFix extends BaseIntentionAction {
       FileEditorManager.getInstance(project).getSelectedTextEditor().getCaretModel().moveCaretRelatively(2, 0, false, false, false);
     });
   }
-}
\ No newline at end of file
+}
diff --git a/code_samples/simple_language_plugin/src/main/java/org/intellij/sdk/language/SimpleReference.java b/code_samples/simple_language_plugin/src/main/java/org/intellij/sdk/language/SimpleReference.java
index 8406b80f5..b9823e9fb 100644
--- a/code_samples/simple_language_plugin/src/main/java/org/intellij/sdk/language/SimpleReference.java
+++ b/code_samples/simple_language_plugin/src/main/java/org/intellij/sdk/language/SimpleReference.java
@@ -12,7 +12,7 @@ import org.jetbrains.annotations.*;
 import java.util.*;
 
 public class SimpleReference extends PsiReferenceBase<PsiElement> implements PsiPolyVariantReference {
-  private String key;
+  private final String key;
   
   public SimpleReference(@NotNull PsiElement element, TextRange textRange) {
     super(element, textRange);