Use a transient field for seen in FindJavaVersion (#533)

Same as in sibling recipe `AboutJavaVersion`

Author: timtebeek

src/main/java/org/openrewrite/java/migrate/search/FindJavaVersion.java

@@ -26,15 +26,15 @@
 import org.openrewrite.java.tree.J;
 
 import java.util.HashSet;
-import java.util.Optional;
 import java.util.Set;
 
 @Value
 @EqualsAndHashCode(callSuper = false)
 public class FindJavaVersion extends Recipe {
 
     transient JavaVersionTable table = new JavaVersionTable(this);
-    private static Set<JavaVersion> seen = new HashSet<>();
+    transient Set<JavaVersion> seen = new HashSet<>();
+
     @Override
     public String getDisplayName() {
         return "Find Java versions in use";
@@ -50,15 +50,10 @@ public TreeVisitor<?, ExecutionContext> getVisitor() {
         return new JavaVisitor<ExecutionContext>() {
             @Override
             public J visitCompilationUnit(J.CompilationUnit cu, ExecutionContext ctx) {
-                Optional<JavaVersion> maybeJv = cu.getMarkers().findFirst(JavaVersion.class);
-                if(!maybeJv.isPresent()) {
-                    return cu;
-                }
-                JavaVersion jv = maybeJv.get();
-                if(!seen.add(jv)) {
-                    return cu;
-                }
-                table.insertRow(ctx, new JavaVersionTable.Row(jv.getSourceCompatibility(), jv.getTargetCompatibility()));
+                cu.getMarkers().findFirst(JavaVersion.class)
+                        .filter(seen::add)
+                        .map(jv -> new JavaVersionTable.Row(jv.getSourceCompatibility(), jv.getTargetCompatibility()))
+                        .ifPresent(row -> table.insertRow(ctx, row));
                 return cu;
             }
         };

src/test/java/org/openrewrite/java/migrate/search/FindJavaVersionTest.java

@@ -16,6 +16,7 @@
 package org.openrewrite.java.migrate.search;
 
 import org.junit.jupiter.api.Test;
+import org.openrewrite.DocumentExample;
 import org.openrewrite.java.marker.JavaVersion;
 import org.openrewrite.java.migrate.table.JavaVersionTable;
 import org.openrewrite.test.RecipeSpec;
@@ -33,7 +34,8 @@ public void defaults(RecipeSpec spec) {
     }
 
     @Test
-    void test() {
+    @DocumentExample
+    void twoClassesWithSameMarkerLeadToOneRow() {
         JavaVersion jv = new JavaVersion(randomId(), "Sam", "Shelter", "17", "8");
         rewriteRun(
           spec -> spec.dataTable(JavaVersionTable.Row.class, rows -> {