[BUG][JAVA] Render enum constants in object property defaults (fixes #24298)

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractJavaCodegen.java

@@ -1558,7 +1558,17 @@ private String toObjectDefaultValue(CodegenProperty cp, Object defaultValue, Map
                     }
 
                     String defaultPropertyExpression = null;
-                    if(ModelUtils.isLongSchema(propertySchema)) {
+                    if(ModelUtils.isEnumSchema(ModelUtils.getReferencedSchema(this.openAPI, propertySchema))) {
+                        // Enum-typed property: render the enum constant (e.g. `OutputFormat.OrderEnum.SIMILARITY`)
+                        // rather than a raw quoted string, which would not compile (see #24298).
+                        CodegenProperty enumProperty = fromProperty(key, propertySchema);
+                        String enumType = enumProperty.isEnum
+                                // an inline enum is generated as a nested class of the containing object type
+                                ? cp.datatypeWithEnum + "." + enumProperty.datatypeWithEnum
+                                // a `$ref` to a named enum is a top-level type
+                                : enumProperty.datatypeWithEnum;
+                        defaultPropertyExpression = enumType + "." + toEnumVarName(value.asText(), enumProperty.dataType);
+                    } else if(ModelUtils.isLongSchema(propertySchema)) {
                         defaultPropertyExpression = value.asText()+"l";
                     } else if(ModelUtils.isIntegerSchema(propertySchema)) {
                         defaultPropertyExpression = value.asText();

modules/openapi-generator/src/test/java/org/openapitools/codegen/java/AbstractJavaCodegenTest.java

@@ -650,6 +650,28 @@ public void toDefaultValueForComposedObjectWithDefaultTest() {
         Assert.assertEquals(rendered, "new " + cp.datatypeWithEnum + "().one(\"one\").two(\"two\")");
     }
 
+    @Test
+    public void toDefaultValueForObjectWithEnumPropertyDefaultTest() {
+        // An object default that contains an enum property must render the enum constant
+        // (e.g. `OutputFormat.OrderEnum.SIMILARITY`) rather than a raw quoted string, which
+        // would not compile (see #24298).
+        ObjectSchema outputFormat = new ObjectSchema();
+        outputFormat.addProperty("order", new StringSchema()._enum(java.util.Arrays.asList("IMPORTANCE", "SIMILARITY")));
+        outputFormat.addProperty("limit", new IntegerSchema());
+        Map<String, Object> defaultValue = new LinkedHashMap<>();
+        defaultValue.put("order", "SIMILARITY");
+        defaultValue.put("limit", 10);
+        outputFormat.setDefault(defaultValue);
+
+        codegen.setOpenAPI(new OpenAPI().components(new Components().addSchemas("OutputFormat", outputFormat)));
+
+        CodegenProperty cp = codegen.fromProperty("format", new Schema<>().$ref("#/components/schemas/OutputFormat"));
+        String rendered = codegen.toDefaultValue(cp, outputFormat);
+
+        Assert.assertEquals(rendered, "new " + cp.datatypeWithEnum + "().order("
+                + cp.datatypeWithEnum + ".OrderEnum.SIMILARITY).limit(10)");
+    }
+
     @Test
     public void dateDefaultValueIsIsoDate() {
         final OpenAPI openAPI = FLATTENED_SPEC.get("3_0/spring/date-time-parameter-types-for-testing");

modules/openapi-generator/src/test/java/org/openapitools/codegen/java/JavaClientCodegenTest.java

@@ -1850,6 +1850,25 @@ public void testJavaClientDefaultValues_issueNoNumber() {
                 .asString().endsWith("= new ArrayList<>();");
     }
 
+    @Test
+    public void testObjectDefaultWithEnumProperty_issue24298() {
+        final Path output = newTempFolder();
+        final CodegenConfigurator configurator = new CodegenConfigurator()
+                .setGeneratorName(JAVA_GENERATOR)
+                .setInputSpec("src/test/resources/bugs/issue_24298.yaml")
+                .setOutputDir(output.toString().replace("\\", "/"));
+
+        Map<String, File> files = new DefaultGenerator().opts(configurator.toClientOptInput()).generate().stream()
+                .collect(Collectors.toMap(File::getName, Function.identity()));
+
+        // The `format` field's default is an OutputFormat whose `order` property is an inline enum. It must
+        // be rendered as the enum constant, not a raw quoted string, otherwise the code does not compile (#24298).
+        JavaFileAssert.assertThat(files.get("Formatter.java"))
+                .assertProperty("format")
+                .asString()
+                .contains("new OutputFormat().order(OutputFormat.OrderEnum.SIMILARITY).limit(10)");
+    }
+
     @Test
     public void testWebClientJsonCreatorWithNullable_issue12790() {
         final Path output = newTempFolder();

modules/openapi-generator/src/test/resources/bugs/issue_24298.yaml

@@ -0,0 +1,25 @@
+openapi: "3.1.0"
+info:
+  title: Enum Default Issue Demo
+  version: 1.0.0
+paths: {}
+components:
+  schemas:
+    OutputFormat:
+      type: object
+      properties:
+        order:
+          type: string
+          enum:
+            - IMPORTANCE
+            - SIMILARITY
+        limit:
+          type: integer
+      default:
+        order: SIMILARITY
+        limit: 10
+    Formatter:
+      type: object
+      properties:
+        format:
+          $ref: '#/components/schemas/OutputFormat'