diff --git a/java/debugger/openapi/src/com/intellij/debugger/engine/DebuggerUtils.java b/java/debugger/openapi/src/com/intellij/debugger/engine/DebuggerUtils.java
index d28d52b6f173..1480db8a5ca7 100644
--- a/java/debugger/openapi/src/com/intellij/debugger/engine/DebuggerUtils.java
+++ b/java/debugger/openapi/src/com/intellij/debugger/engine/DebuggerUtils.java
@@ -78,17 +78,11 @@ public abstract class DebuggerUtils {
       }
       if (value instanceof ObjectReference) {
         if (value instanceof ArrayReference) {
-          final StringBuilder builder = new StringBuilder();
-          builder.append("[");
-          for (Iterator<Value> iterator = ((ArrayReference)value).getValues().iterator(); iterator.hasNext();) {
-            final Value element = iterator.next();
-            builder.append(getValueAsString(evaluationContext, element));
-            if (iterator.hasNext()) {
-              builder.append(",");
-            }
+          final StringJoiner joiner = new StringJoiner(",", "[", "]");
+          for (final Value element : ((ArrayReference)value).getValues()) {
+            joiner.add(getValueAsString(evaluationContext, element));
           }
-          builder.append("]");
-          return builder.toString();
+          return joiner.toString();
         }
 
         final ObjectReference objRef = (ObjectReference)value;
diff --git a/java/idea-ui/src/com/intellij/ide/util/importProject/ProjectLayoutPanel.java b/java/idea-ui/src/com/intellij/ide/util/importProject/ProjectLayoutPanel.java
index bff5d1d44a94..c3a20e2e3e6b 100644
--- a/java/idea-ui/src/com/intellij/ide/util/importProject/ProjectLayoutPanel.java
+++ b/java/idea-ui/src/com/intellij/ide/util/importProject/ProjectLayoutPanel.java
@@ -240,15 +240,11 @@ abstract class ProjectLayoutPanel<T> extends JPanel {
 
       final Collection<? extends DetectedProjectRoot> sourceRoots = moduleDescriptor.getSourceRoots();
       if (sourceRoots.size() > 0) {
-        builder.append(" [");
-        for (Iterator<? extends DetectedProjectRoot> it = sourceRoots.iterator(); it.hasNext();) {
-          DetectedProjectRoot root = it.next();
-          builder.append(root.getDirectory().getName());
-          if (it.hasNext()) {
-            builder.append(",");
-          }
+        StringJoiner joiner = new StringJoiner(",", " [", "]");
+        for (DetectedProjectRoot root : sourceRoots) {
+          joiner.add(root.getDirectory().getName());
         }
-        builder.append("]");
+        builder.append(joiner);
       }
       return builder.toString();
     }
diff --git a/java/java-analysis-impl/src/com/intellij/codeInspection/dataFlow/rangeSet/LongRangeSet.java b/java/java-analysis-impl/src/com/intellij/codeInspection/dataFlow/rangeSet/LongRangeSet.java
index a117e2317ea2..ee15e287a6dd 100644
--- a/java/java-analysis-impl/src/com/intellij/codeInspection/dataFlow/rangeSet/LongRangeSet.java
+++ b/java/java-analysis-impl/src/com/intellij/codeInspection/dataFlow/rangeSet/LongRangeSet.java
@@ -2100,12 +2100,10 @@ public abstract class LongRangeSet {
 
     @Override
     public String toString() {
-      StringBuilder sb = new StringBuilder("{");
+      StringJoiner sb = new StringJoiner(", ", "{", "}");
       for (int i = 0; i < myRanges.length; i += 2) {
-        if (i > 0) sb.append(", ");
-        sb.append(LongRangeSet.toString(myRanges[i], myRanges[i + 1]));
+        sb.add(LongRangeSet.toString(myRanges[i], myRanges[i + 1]));
       }
-      sb.append("}");
       return sb.toString();
     }
   }
diff --git a/java/java-psi-api/src/com/intellij/psi/PsiIntersectionType.java b/java/java-psi-api/src/com/intellij/psi/PsiIntersectionType.java
index 2640e4114118..43f65f0fb890 100644
--- a/java/java-psi-api/src/com/intellij/psi/PsiIntersectionType.java
+++ b/java/java-psi-api/src/com/intellij/psi/PsiIntersectionType.java
@@ -9,6 +9,7 @@ import com.intellij.psi.util.TypeConversionUtil;
 import org.jetbrains.annotations.NotNull;
 
 import java.util.*;
+import java.util.stream.Collectors;
 
 /**
  * Intersection types arise in a process of computing least upper bound.
@@ -169,12 +170,7 @@ public class PsiIntersectionType extends PsiType.Stub {
 
   @Override
   public String toString() {
-    StringBuilder sb = new StringBuilder("PsiIntersectionType: ");
-    for (int i = 0; i < myConjuncts.length; i++) {
-      if (i > 0) sb.append(", ");
-      sb.append(myConjuncts[i].getPresentableText());
-    }
-    return sb.toString();
+    return Arrays.stream(myConjuncts).map(PsiType::getPresentableText).collect(Collectors.joining(", ", "PsiIntersectionType: ", ""));
   }
 
   public String getConflictingConjunctsMessage() {
diff --git a/java/java-psi-api/src/com/intellij/psi/util/PsiFormatUtil.java b/java/java-psi-api/src/com/intellij/psi/util/PsiFormatUtil.java
index 4d607097f7b9..4b54636c4ce5 100644
--- a/java/java-psi-api/src/com/intellij/psi/util/PsiFormatUtil.java
+++ b/java/java-psi-api/src/com/intellij/psi/util/PsiFormatUtil.java
@@ -10,6 +10,8 @@ import org.intellij.lang.annotations.MagicConstant;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
+import java.util.StringJoiner;
+
 public class PsiFormatUtil extends PsiFormatUtilBase {
   @MagicConstant(flags = {
     SHOW_MODIFIERS, SHOW_TYPE, TYPE_AFTER, SHOW_CONTAINING_CLASS, SHOW_FQ_NAME, SHOW_NAME, SHOW_MODIFIERS,
@@ -335,19 +337,17 @@ public class PsiFormatUtil extends PsiFormatUtilBase {
   }
 
   private static String formatReferenceList(PsiReferenceList list, int options) {
-    StringBuilder buffer = new StringBuilder();
+    StringJoiner buffer = new StringJoiner(", ");
     if (BitUtil.isSet(options, SHOW_RAW_TYPE)) {
       PsiClassType[] types = list.getReferencedTypes();
-      for (int i = 0; i < types.length; i++) {
-        if (i > 0) buffer.append(", ");
-        buffer.append(formatType(types[i], options, PsiSubstitutor.EMPTY));
+      for (PsiClassType type : types) {
+        buffer.add(formatType(type, options, PsiSubstitutor.EMPTY));
       }
     }
     else {
       PsiJavaCodeReferenceElement[] refs = list.getReferenceElements();
-      for (int i = 0; i < refs.length; i++) {
-        if (i > 0) buffer.append(", ");
-        buffer.append(formatReference(refs[i], options));
+      for (PsiJavaCodeReferenceElement ref : refs) {
+        buffer.add(formatReference(ref, options));
       }
     }
     return buffer.toString();
diff --git a/java/java-psi-impl/src/com/intellij/psi/impl/light/LightReferenceParameterList.java b/java/java-psi-impl/src/com/intellij/psi/impl/light/LightReferenceParameterList.java
index 0e5f1dfee89c..c9beadaf1a36 100644
--- a/java/java-psi-impl/src/com/intellij/psi/impl/light/LightReferenceParameterList.java
+++ b/java/java-psi-impl/src/com/intellij/psi/impl/light/LightReferenceParameterList.java
@@ -20,6 +20,8 @@ import com.intellij.psi.*;
 import com.intellij.psi.impl.PsiImplUtil;
 import org.jetbrains.annotations.NotNull;
 
+import java.util.StringJoiner;
+
 /**
  *  @author dsl
  */
@@ -35,16 +37,10 @@ public class LightReferenceParameterList extends LightElement implements PsiRefe
 
   private String calculateText() {
     if (myTypeElements.length == 0) return "";
-    final StringBuilder buffer = new StringBuilder();
-    buffer.append("<");
-    for (int i = 0; i < myTypeElements.length; i++) {
-      PsiTypeElement type = myTypeElements[i];
-      if (i > 0) {
-        buffer.append(",");
-      }
-      buffer.append(type.getText());
+    final StringJoiner buffer = new StringJoiner(",", "<", ">");
+    for (PsiTypeElement type : myTypeElements) {
+      buffer.add(type.getText());
     }
-    buffer.append(">");
     return buffer.toString();
   }
 
diff --git a/platform/core-api/src/com/intellij/psi/search/LocalSearchScope.java b/platform/core-api/src/com/intellij/psi/search/LocalSearchScope.java
index 14ab5985fc19..c024f607153c 100644
--- a/platform/core-api/src/com/intellij/psi/search/LocalSearchScope.java
+++ b/platform/core-api/src/com/intellij/psi/search/LocalSearchScope.java
@@ -35,6 +35,7 @@ import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
 import java.util.*;
+import java.util.stream.Collectors;
 
 public class LocalSearchScope extends SearchScope {
   private static final Logger LOG = Logger.getInstance("#com.intellij.psi.search.LocalSearchScope");
@@ -198,16 +199,8 @@ public class LocalSearchScope extends SearchScope {
 
   @Override
   public String toString() {
-    StringBuilder result = new StringBuilder();
-    for (int i = 0; i < myScope.length; i++) {
-      final PsiElement element = myScope[i];
-      if (i > 0) {
-        result.append(",");
-      }
-      result.append(element);
-    }
     //noinspection HardCodedStringLiteral
-    return "LocalSearchScope:" + result;
+    return Arrays.stream(myScope).map(String::valueOf).collect(Collectors.joining(",", "LocalSearchScope:", ""));
   }
 
   @Override
diff --git a/platform/lang-api/src/com/intellij/psi/codeStyle/SoftMargins.java b/platform/lang-api/src/com/intellij/psi/codeStyle/SoftMargins.java
index a0d58fdfe502..501c9a4c218a 100644
--- a/platform/lang-api/src/com/intellij/psi/codeStyle/SoftMargins.java
+++ b/platform/lang-api/src/com/intellij/psi/codeStyle/SoftMargins.java
@@ -23,6 +23,7 @@ import org.jetbrains.annotations.Nullable;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
+import java.util.stream.Collectors;
 
 class SoftMargins implements Cloneable {
 
@@ -39,7 +40,6 @@ class SoftMargins implements Cloneable {
     if (valueList != null) {
       String[] values = valueList.split(",\\s*");
       myValues = new ArrayList<>(values.length);
-      int i = 0;
       for (String value : values) {
         try {
           myValues.add(Integer.parseInt(value));
@@ -87,14 +87,10 @@ class SoftMargins implements Cloneable {
 
   @Override
   public String toString() {
-    StringBuilder sb = new StringBuilder();
-    if (myValues != null) {
-      for (int margin: myValues) {
-        if (sb.length() > 0) sb.append(",");
-        sb.append(margin);
-      }
+    if (myValues == null) {
+      return "";
     }
-    return sb.toString();
+    return myValues.stream().map(String::valueOf).collect(Collectors.joining(","));
   }
 
   public void serializeInto(@NotNull Element element) {