piercifani · Nov 4, 2026
@@ -61,13 +61,15 @@ extension ExtractedFunc {
     }
 
     let returnsBoolean = self.functionSignature.result.type.asNominalTypeDeclaration?.knownTypeKind == .bool
+    // A property named with backticks, such as `default`, is `getDefault` in Java.
+    let name = self.name.unescapedSwiftName
 
     if !returnsBoolean {
-      return "get\(self.name.firstCharacterUppercased)"
-    } else if !self.name.hasJavaBooleanNamingConvention {
-      return "is\(self.name.firstCharacterUppercased)"
+      return "get\(name.firstCharacterUppercased)"
+    } else if !name.hasJavaBooleanNamingConvention {
+      return "is\(name.firstCharacterUppercased)"
     } else {
-      return self.name
+      return name
     }
   }
 
@@ -85,13 +87,14 @@ extension ExtractedFunc {
     }
 
     let isBooleanSetter = self.functionSignature.parameters.first?.type.asNominalTypeDeclaration?.knownTypeKind == .bool
+    let name = self.name.unescapedSwiftName
 
-    if isBooleanSetter && self.name.hasJavaBooleanNamingConvention {
+    if isBooleanSetter && name.hasJavaBooleanNamingConvention {
       // Safe to force unwrap due to `hasJavaBooleanNamingConvention` check.
-      let propertyName = self.name.split(separator: "is", maxSplits: 1).last!
+      let propertyName = name.split(separator: "is", maxSplits: 1).last!
       return "set\(propertyName)"
     } else {
-      return "set\(self.name.firstCharacterUppercased)"
+      return "set\(name.firstCharacterUppercased)"
     }
   }
 }
@@ -59,7 +59,7 @@ extension JNISwift2JavaGenerator {
 
   private func renderEscapingClosureApplySignature(_ type: SwiftFunctionType) -> String {
     let params = type.parameters.enumerated().map { idx, param -> String in
-      let name = param.parameterName ?? "_\(idx)"
+      let name = (param.parameterName ?? "_\(idx)").javaSafeIdentifier
       let typeName = param.type.description
       return "_ \(name): \(typeName)"
     }

@@ -149,7 +149,7 @@ extension JNISwift2JavaGenerator {
     ) throws -> SyntheticEscapingClosureFunctionType {
       let parameterConversions = try functionType.parameters.enumerated().map { idx, param in
         try self.translateParameter(
-          parameterName: param.parameterName ?? "_\(idx)",
+          parameterName: (param.parameterName ?? "_\(idx)").javaSafeIdentifier,
           type: param.type
         )
       }

@@ -136,7 +136,7 @@ extension JNISwift2JavaGenerator {
       let methodName = "" // TODO: Used for closures, replace with better name?
 
       let parameterResults = try enumCase.parameters.enumerated().map { idx, parameter in
-        let resultName = parameter.name ?? "arg\(idx)"
+        let resultName = (parameter.name ?? "arg\(idx)").javaSafeIdentifier
         let translatedResult = try self.translateResult(
           swiftType: parameter.type,
           methodName: methodName,
@@ -226,7 +226,7 @@ extension JNISwift2JavaGenerator {
       // Closures.
       var funcTypes: [TranslatedFunctionType] = []
       for (idx, param) in decl.functionSignature.parameters.enumerated() {
-        let parameterName = param.parameterName ?? "_\(idx)"
+        let parameterName = (param.parameterName ?? "_\(idx)").javaSafeIdentifier
 
         switch param.type {
         case .function(let funcTy):
@@ -303,7 +303,7 @@ extension JNISwift2JavaGenerator {
       var translatedParams: [TranslatedParameter] = []
 
       for (i, param) in swiftType.parameters.enumerated() {
-        let paramName = param.parameterName ?? "_\(i)"
+        let paramName = (param.parameterName ?? "_\(i)").javaSafeIdentifier
         translatedParams.append(
           try translateParameter(
             swiftType: param.type,
@@ -387,7 +387,7 @@ extension JNISwift2JavaGenerator {
       genericRequirements: [SwiftGenericRequirement],
     ) throws -> [TranslatedParameter] {
       try parameters.enumerated().map { idx, param in
-        let parameterName = param.name ?? "arg\(idx)"
+        let parameterName = (param.name ?? "arg\(idx)").javaSafeIdentifier
         return try translateParameter(
           swiftType: param.type,
           parameterName: parameterName,

@@ -422,7 +422,7 @@ extension JNISwift2JavaGenerator {
       // Non-escaping closures use the legacy translation
       var parameters = [NativeParameter]()
       for (i, parameter) in functionType.parameters.enumerated() {
-        let closureParamName = parameter.parameterName ?? "_\(i)"
+        let closureParamName = (parameter.parameterName ?? "_\(i)").javaSafeIdentifier
         let closureParameter = try translateClosureParameter(
           parameter.type,
           parameterName: closureParamName
@@ -1726,7 +1726,7 @@ extension JNISwift2JavaGenerator {
 
         let fn = syntheticFunction.functionType
         let parameterNames = fn.parameters.enumerated().map { idx, param in
-          param.parameterName ?? "_\(idx)"
+          (param.parameterName ?? "_\(idx)").javaSafeIdentifier
         }
         let closureParameters = parameterNames.joined(separator: .comma)
         let isVoid = fn.resultType.isVoid

@@ -458,7 +458,7 @@ extension JNISwift2JavaGenerator {
         }.joined(separator: .comma)
         printer.printBraceBlock("fileprivate func getAs\(enumCase.name)() -> (\(associatedValueTypes))?") { printer in
           let params = enumCase.original.parameters.enumerated().map { i, param in
-            param.name ?? "_\(i)"
+            (param.name ?? "_\(i)").javaSafeIdentifier
           }.joined(separator: .comma)
           printer.printIfBlock("case let .\(enumCase.original.name)(\(params)) = self") { printer in
             printer.print("return (\(params))")

@@ -73,7 +73,7 @@ package struct JavaIdentifierFactory {
         Self.javaOperatorName(decl.name)
       }
     var methodName = baseName + paramsSuffix(decl, baseName: baseName)
-    if Self.javaKeywords.contains(methodName) {
+    if Self.javaKeywords.contains(methodName) || Self.finalObjectMethods.contains(methodName) {
       methodName += "_"
     }
     return methodName
@@ -167,4 +167,25 @@ package struct JavaIdentifierFactory {
     /// literals
     "true", "false", "null",
   ]
+
+  /// Final methods of `java.lang.Object`, which a generated method can't declare again.
+  static let finalObjectMethods: Set<String> = ["getClass", "notify", "notifyAll", "wait"]
+
+  /// Swift keywords that can't name a parameter or a local variable without backticks.
+  static let reservedSwiftKeywords: Set<String> = [
+    "associatedtype", "class", "deinit", "enum", "extension", "fileprivate", "func", "import", "init", "inout",
+    "internal", "let", "operator", "precedencegroup", "private", "protocol", "public", "rethrows", "static",
+    "struct", "subscript", "typealias", "var", "break", "case", "catch", "continue", "default", "defer", "do",
+    "else", "fallthrough", "for", "guard", "if", "in", "repeat", "return", "switch", "throw", "where", "while",
+    "Any", "as", "false", "is", "nil", "self", "Self", "super", "throws", "true", "try",
+  ]
+}
+
+extension String {
+  /// This name, made usable as a parameter or local variable in both the generated Java and Swift: a Java or
+  /// Swift keyword such as `long` or `default` gets a `_` suffix.
+  package var javaSafeIdentifier: String {
+    JavaIdentifierFactory.javaKeywords.contains(self) || JavaIdentifierFactory.reservedSwiftKeywords.contains(self)
+      ? self + "_" : self
+  }
 }
@@ -41,12 +41,12 @@ struct JNIJavaKitTests {
          * public func function(javaLong: JavaLong, javaInteger: JavaInteger, int: Int64)
          * }
          */
-        public static void function(java.lang.Long javaLong, java.lang.Integer javaInteger, long int) {
-          SwiftModule.$function(javaLong, javaInteger, int);
+        public static void function(java.lang.Long javaLong, java.lang.Integer javaInteger, long int_) {
+          SwiftModule.$function(javaLong, javaInteger, int_);
         }
         """,
         """
-        private static native void $function(java.lang.Long javaLong, java.lang.Integer javaInteger, long int);
+        private static native void $function(java.lang.Long javaLong, java.lang.Integer javaInteger, long int_);
         """,
       ]
     )
@@ -63,14 +63,14 @@ struct JNIJavaKitTests {
       expectedChunks: [
         """
         @_cdecl("Java_com_example_swift_SwiftModule__00024function__Ljava_lang_Long_2Ljava_lang_Integer_2J")
-        public func Java_com_example_swift_SwiftModule__00024function__Ljava_lang_Long_2Ljava_lang_Integer_2J(environment: UnsafeMutablePointer<JNIEnv?>!, thisClass: jclass, javaLong: jobject?, javaInteger: jobject?, int: jlong) {
+        public func Java_com_example_swift_SwiftModule__00024function__Ljava_lang_Long_2Ljava_lang_Integer_2J(environment: UnsafeMutablePointer<JNIEnv?>!, thisClass: jclass, javaLong: jobject?, javaInteger: jobject?, int_: jlong) {
           guard let javaLong_unwrapped$ = javaLong else {
             fatalError("javaLong was null in call to \\(#function), but Swift requires non-optional!")
           }
           guard let javaInteger_unwrapped$ = javaInteger else {
             fatalError("javaInteger was null in call to \\(#function), but Swift requires non-optional!")
           }
-          SwiftModule.function(javaLong: JavaLong(javaThis: javaLong_unwrapped$, environment: environment), javaInteger: JavaInteger(javaThis: javaInteger_unwrapped$, environment: environment), int: Int64(fromJNI: int, in: environment))
+          SwiftModule.function(javaLong: JavaLong(javaThis: javaLong_unwrapped$, environment: environment), javaInteger: JavaInteger(javaThis: javaInteger_unwrapped$, environment: environment), int: Int64(fromJNI: int_, in: environment))
         }
         """
       ]

@@ -139,4 +139,105 @@ struct JavaKeywordTests {
       ]
     )
   }
+
+  @Test
+  func jniParameterNames() throws {
+    let text =
+      """
+      public struct Side {
+        public func scale(double: Double, int: Int64, `default`: Bool) -> Double
+      }
+      """
+
+    try assertOutput(
+      input: text,
+      .jni,
+      .java,
+      detectChunkByInitialLines: 1,
+      expectedChunks: [
+        "public double scale(double double_, long int_, boolean default_) {",
+        "return Side.$scale(double_, int_, default_, this.$memoryAddress());",
+      ]
+    )
+
+    try assertOutput(
+      input: text,
+      .jni,
+      .swift,
+      detectChunkByInitialLines: 1,
+      expectedChunks: [
+        "thisClass: jclass, double_: jdouble, int_: jlong, default_: jboolean, selfPointer: jlong) -> jdouble {",
+        "scale(double: Double(fromJNI: double_, in: environment), int: Int64(fromJNI: int_, in: environment), default: Bool(fromJNI: default_, in: environment))",
+      ]
+    )
+  }
+
+  @Test
+  func jniEnumCasePayloadNames() throws {
+    let text =
+      """
+      public enum Pricing {
+        case quote(slug: String, long: Int64)
+      }
+      """
+
+    try assertOutput(
+      input: text,
+      .jni,
+      .java,
+      detectChunkByInitialLines: 1,
+      expectedChunks: [
+        "record Quote(java.lang.String slug, long long_) implements Case {}"
+      ]
+    )
+
+    try assertOutput(
+      input: text,
+      .jni,
+      .swift,
+      detectChunkByInitialLines: 1,
+      expectedChunks: [
+        "if case let .quote(slug, long_) = self {"
+      ]
+    )
+  }
+
+  @Test
+  func backtickedPropertyName() throws {
+    try assertOutput(
+      input: """
+        public struct Side {
+          public static var `default`: Side
+        }
+        """,
+      .jni,
+      .java,
+      detectChunkByInitialLines: 1,
+      expectedChunks: [
+        "public static Side getDefault(SwiftArena swiftArena) {"
+      ],
+      notExpectedChunks: ["get`default`"]
+    )
+  }
+
+  @Test
+  func finalObjectMethodNames() throws {
+    try assertOutput(
+      input: """
+        public struct Lock {
+          public var `class`: String
+          public func wait()
+          public func notify(_ count: Int64)
+        }
+        """,
+      .jni,
+      .java,
+      detectChunkByInitialLines: 1,
+      expectedChunks: [
+        "public java.lang.String getClass_() {",
+        "public void wait_() {",
+        "public void notify_(long count) {",
+      ]
+    )
+  }
 }