diff --git a/j2k/src/org/jetbrains/kotlin/j2k/ExpressionConverter.kt b/j2k/src/org/jetbrains/kotlin/j2k/ExpressionConverter.kt
index 81c8a949c61..0d96fe6abb6 100644
--- a/j2k/src/org/jetbrains/kotlin/j2k/ExpressionConverter.kt
+++ b/j2k/src/org/jetbrains/kotlin/j2k/ExpressionConverter.kt
@@ -32,11 +32,11 @@ import org.jetbrains.kotlin.psi.psiUtil.getStrictParentOfType
 import org.jetbrains.kotlin.psi.psiUtil.isExtensionDeclaration
 import org.jetbrains.kotlin.resolve.jvm.JvmPrimitiveType
 
-trait ExpressionConverter {
+interface ExpressionConverter {
     fun convertExpression(expression: PsiExpression, codeConverter: CodeConverter): Expression
 }
 
-trait SpecialExpressionConverter {
+interface SpecialExpressionConverter {
     fun convertExpression(expression: PsiExpression, codeConverter: CodeConverter): Expression?
 }
 
diff --git a/j2k/src/org/jetbrains/kotlin/j2k/ForConverter.kt b/j2k/src/org/jetbrains/kotlin/j2k/ForConverter.kt
index 8dfd6d108b2..0bf4854f4f4 100644
--- a/j2k/src/org/jetbrains/kotlin/j2k/ForConverter.kt
+++ b/j2k/src/org/jetbrains/kotlin/j2k/ForConverter.kt
@@ -252,7 +252,7 @@ class ForConverter(
         if (indices == null) return null
 
         return if (reversed)
-            MethodCallExpression.build(indices!!.assignNoPrototype(), "reversed", listOf(), listOf(), false)
+            MethodCallExpression.build(indices.assignNoPrototype(), "reversed", listOf(), listOf(), false)
         else
             indices
     }
diff --git a/j2k/src/org/jetbrains/kotlin/j2k/JavaToKotlinConverter.kt b/j2k/src/org/jetbrains/kotlin/j2k/JavaToKotlinConverter.kt
index 5ea64db9afa..c6d64c265d5 100644
--- a/j2k/src/org/jetbrains/kotlin/j2k/JavaToKotlinConverter.kt
+++ b/j2k/src/org/jetbrains/kotlin/j2k/JavaToKotlinConverter.kt
@@ -36,13 +36,11 @@ import org.jetbrains.kotlin.j2k.usageProcessing.UsageProcessing
 import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.psi.*
 import org.jetbrains.kotlin.psi.psiUtil.isAncestor
-import org.jetbrains.kotlin.psi.psiUtil.parents
 import org.jetbrains.kotlin.psi.psiUtil.parentsWithSelf
 import org.jetbrains.kotlin.resolve.BindingContext
 import java.util.ArrayList
 import java.util.Comparator
 import java.util.LinkedHashMap
-import kotlin.properties.Delegates
 
 public interface PostProcessor {
     public fun analyzeFile(file: JetFile, range: TextRange?): BindingContext
@@ -178,7 +176,7 @@ public class JavaToKotlinConverter(
             val file: PsiFile,
             val processings: Collection<UsageProcessing>
     ) {
-        val depth: Int by Delegates.lazy { target.parentsWithSelf.takeWhile { it !is PsiFile }.count() }
+        val depth: Int by lazy { target.parentsWithSelf.takeWhile { it !is PsiFile }.count() }
     }
 
     private fun buildExternalCodeProcessing(
diff --git a/j2k/src/org/jetbrains/kotlin/j2k/ReferenceSearcher.kt b/j2k/src/org/jetbrains/kotlin/j2k/ReferenceSearcher.kt
index 91082618d1d..53faa602e8f 100644
--- a/j2k/src/org/jetbrains/kotlin/j2k/ReferenceSearcher.kt
+++ b/j2k/src/org/jetbrains/kotlin/j2k/ReferenceSearcher.kt
@@ -27,7 +27,7 @@ import com.intellij.psi.search.searches.ReferencesSearch
 import org.jetbrains.kotlin.idea.JetLanguage
 import java.util.ArrayList
 
-public trait ReferenceSearcher {
+public interface ReferenceSearcher {
     fun findLocalUsages(element: PsiElement, scope: PsiElement): Collection<PsiReference>
     fun hasInheritors(`class`: PsiClass): Boolean
     fun hasOverrides(method: PsiMethod): Boolean
diff --git a/j2k/src/org/jetbrains/kotlin/j2k/ResolverForConverter.kt b/j2k/src/org/jetbrains/kotlin/j2k/ResolverForConverter.kt
index 4e2795df619..4124857ee64 100644
--- a/j2k/src/org/jetbrains/kotlin/j2k/ResolverForConverter.kt
+++ b/j2k/src/org/jetbrains/kotlin/j2k/ResolverForConverter.kt
@@ -19,7 +19,7 @@ package org.jetbrains.kotlin.j2k
 import org.jetbrains.kotlin.psi.JetDeclaration
 import org.jetbrains.kotlin.descriptors.DeclarationDescriptor
 
-public trait ResolverForConverter {
+public interface ResolverForConverter {
     public fun resolveToDescriptor(declaration: JetDeclaration): DeclarationDescriptor?
 }
 
diff --git a/j2k/src/org/jetbrains/kotlin/j2k/StatementConverter.kt b/j2k/src/org/jetbrains/kotlin/j2k/StatementConverter.kt
index 343f3cc14f4..01f1bcaeab9 100644
--- a/j2k/src/org/jetbrains/kotlin/j2k/StatementConverter.kt
+++ b/j2k/src/org/jetbrains/kotlin/j2k/StatementConverter.kt
@@ -20,11 +20,11 @@ import com.intellij.psi.*
 import org.jetbrains.kotlin.j2k.ast.*
 import java.util.ArrayList
 
-trait StatementConverter {
+interface StatementConverter {
     fun convertStatement(statement: PsiStatement, codeConverter: CodeConverter): Statement
 }
 
-trait SpecialStatementConverter {
+interface SpecialStatementConverter {
     fun convertStatement(statement: PsiStatement, codeConverter: CodeConverter): Statement?
 }
 
diff --git a/j2k/src/org/jetbrains/kotlin/j2k/usageProcessing/UsageProcessing.kt b/j2k/src/org/jetbrains/kotlin/j2k/usageProcessing/UsageProcessing.kt
index 4137d04d942..9da29d70705 100644
--- a/j2k/src/org/jetbrains/kotlin/j2k/usageProcessing/UsageProcessing.kt
+++ b/j2k/src/org/jetbrains/kotlin/j2k/usageProcessing/UsageProcessing.kt
@@ -22,20 +22,20 @@ import org.jetbrains.kotlin.j2k.CodeConverter
 import org.jetbrains.kotlin.j2k.SpecialExpressionConverter
 import org.jetbrains.kotlin.j2k.ast.Expression
 
-trait UsageProcessing {
+interface UsageProcessing {
     val targetElement: PsiElement
     val convertedCodeProcessor: ConvertedCodeProcessor?
     val javaCodeProcessor: ExternalCodeProcessor?
     val kotlinCodeProcessor: ExternalCodeProcessor?
 }
 
-trait ConvertedCodeProcessor {
+interface ConvertedCodeProcessor {
     fun convertVariableUsage(expression: PsiReferenceExpression, codeConverter: CodeConverter): Expression? = null
 
     fun convertMethodUsage(methodCall: PsiMethodCallExpression, codeConverter: CodeConverter): Expression? = null
 }
 
-trait ExternalCodeProcessor {
+interface ExternalCodeProcessor {
     fun processUsage(reference: PsiReference): Array<PsiReference>?
 }
 
diff --git a/j2k/tests/org/jetbrains/kotlin/j2k/AbstractJavaToKotlinConverterForWebDemoTest.kt b/j2k/tests/org/jetbrains/kotlin/j2k/AbstractJavaToKotlinConverterForWebDemoTest.kt
index 0bb988aec47..91367d0992c 100644
--- a/j2k/tests/org/jetbrains/kotlin/j2k/AbstractJavaToKotlinConverterForWebDemoTest.kt
+++ b/j2k/tests/org/jetbrains/kotlin/j2k/AbstractJavaToKotlinConverterForWebDemoTest.kt
@@ -112,7 +112,7 @@ public abstract class AbstractJavaToKotlinConverterForWebDemoTest : TestCase() {
                     }
                 }
             }
-            classLoader = classLoader?.getParent()
+            classLoader = classLoader.getParent()
         }
         return null
     }