IDEA-167088 Stream API migration: support simple joining cases: fixed AT_WANTED_PLACE case

java/java-impl/src/com/intellij/codeInspection/streamMigration/CollectMigration.java

@@ -561,8 +561,14 @@ class CollectMigration extends BaseStreamApiMigration {
     @Override
     void cleanUp() {
       PsiLocalVariable target = getTargetVariable();
-      target.getTypeElement()
-        .replace(JavaPsiFacade.getElementFactory(target.getProject()).createTypeElementFromText(CommonClassNames.JAVA_LANG_STRING, target));
+      PsiElementFactory factory = JavaPsiFacade.getElementFactory(target.getProject());
+      target.getTypeElement().replace(factory.createTypeElementFromText(CommonClassNames.JAVA_LANG_STRING, target));
+      if (getStatus() == InitializerUsageStatus.AT_WANTED_PLACE) {
+        PsiExpression initializer = target.getInitializer();
+        if (initializer != null) {
+          initializer.replace(factory.createExpressionFromText("\"\"", target));
+        }
+      }
       Collection<PsiReference> usages = ReferencesSearch.search(target).findAll();
       for (PsiReference usage : usages) {
         PsiElement element = usage.getElement();

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/streamApiMigration/afterJoiningReused.java

@@ -0,0 +1,15 @@
+// "Replace with collect" "true"
+
+import java.util.List;
+import java.util.stream.Collectors;
+
+public class Test {
+  static String test(List<String> list) {
+    String sb = "";
+    if(!list.isEmpty()) {
+        sb = list.stream().filter(s -> !s.isEmpty()).collect(Collectors.joining());
+    }
+    String s = sb;
+    return s.trim();
+  }
+}

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/streamApiMigration/beforeJoiningInitialValue.java

@@ -0,0 +1,16 @@
+// "Replace with collect" "false"
+
+import java.util.List;
+
+public class Test {
+  static String test(List<String> list) {
+    // Not supported for now
+    StringBuilder sb = new StringBuilder("initial");
+    for (String s : li<caret>st) {
+      if (!s.isEmpty()) {
+        sb.append(s);
+      }
+    }
+    return sb.toString().trim();
+  }
+}

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/streamApiMigration/beforeJoiningReused.java

@@ -0,0 +1,18 @@
+// "Replace with collect" "true"
+
+import java.util.List;
+
+public class Test {
+  static String test(List<String> list) {
+    StringBuffer sb = new StringBuffer();
+    if(!list.isEmpty()) {
+      for (String s : li<caret>st) {
+        if (!s.isEmpty()) {
+          sb.append(s);
+        }
+      }
+    }
+    String s = sb.toString();
+    return s.trim();
+  }
+}