IDEA-161260 Stream API Migration: support findFirst() patterns

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

@@ -0,0 +1,10 @@
+// "Replace with findFirst()" "true"
+
+import java.util.Collection;
+import java.util.List;
+
+public class Main {
+  public static String find(List<List<String>> list) {
+      return list.stream().flatMap(Collection::stream).filter(string -> string.startsWith("ABC")).findFirst().map(string -> string.substring(3)).orElse("");
+  }
+}

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

@@ -0,0 +1,13 @@
+// "Replace with findFirst()" "true"
+
+import java.util.Collection;
+import java.util.List;
+
+public class Main {
+  public static String find(List<List<String>> list) {
+    if(list != null) {
+        return list.stream().flatMap(Collection::stream).filter(string -> string.startsWith("ABC")).findFirst().orElse(null);
+    }
+    return null;
+  }
+}

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

@@ -0,0 +1,16 @@
+// "Replace with findFirst()" "true"
+
+import java.util.List;
+
+public class Main {
+  public static String find(List<List<String>> list) {
+    for(List<String> innerList : li<caret>st) {
+      for(String string : innerList) {
+        if(string.startsWith("ABC")) {
+          return string.substring(3);
+        }
+      }
+    }
+    return "";
+  }
+}

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

@@ -0,0 +1,18 @@
+// "Replace with findFirst()" "true"
+
+import java.util.List;
+
+public class Main {
+  public static String find(List<List<String>> list) {
+    if(list != null) {
+      for (List<String> innerList : lis<caret>t) {
+        for (String string : innerList) {
+          if (string.startsWith("ABC")) {
+            return string;
+          }
+        }
+      }
+    }
+    return null;
+  }
+}