Android: Fix JavaClassWrapper so it actually works

doc/classes/JavaClass.xml

@@ -1,13 +1,33 @@
 <?xml version="1.0" encoding="UTF-8" ?>
 <class name="JavaClass" inherits="RefCounted" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="../class.xsd">
 	<brief_description>
-		Represents an object from the Java Native Interface.
+		Represents a class from the Java Native Interface.
 	</brief_description>
 	<description>
-		Represents an object from the Java Native Interface. It is returned from [method JavaClassWrapper.wrap].
-		[b]Note:[/b] This class only works on Android. For any other build, this class does nothing.
+		Represents a class from the Java Native Interface. It is returned from [method JavaClassWrapper.wrap].
+		[b]Note:[/b] This class only works on Android. On any other platform, this class does nothing.
 		[b]Note:[/b] This class is not to be confused with [JavaScriptObject].
 	</description>
 	<tutorials>
 	</tutorials>
+	<methods>
+		<method name="get_java_class_name" qualifiers="const">
+			<return type="String" />
+			<description>
+				Returns the Java class name.
+			</description>
+		</method>
+		<method name="get_java_method_list" qualifiers="const">
+			<return type="Dictionary[]" />
+			<description>
+				Returns the object's Java methods and their signatures as an [Array] of dictionaries, in the same format as [method Object.get_method_list].
+			</description>
+		</method>
+		<method name="get_java_parent_class" qualifiers="const">
+			<return type="JavaClass" />
+			<description>
+				Returns a [JavaClass] representing the Java parent class of this class.
+			</description>
+		</method>
+	</methods>
 </class>

doc/classes/JavaClassWrapper.xml

@@ -6,6 +6,15 @@
 	<description>
 		The JavaClassWrapper singleton provides a way for the Godot application to send and receive data through the [url=https://developer.android.com/training/articles/perf-jni]Java Native Interface[/url] (JNI).
 		[b]Note:[/b] This singleton is only available in Android builds.
+		[codeblock]
+		var LocalDateTime = JavaClassWrapper.wrap("java.time.LocalDateTime")
+		var DateTimeFormatter = JavaClassWrapper.wrap("java.time.format.DateTimeFormatter")
+
+		var datetime = LocalDateTime.now()
+		var formatter = DateTimeFormatter.ofPattern("dd-MM-yyyy HH:mm:ss")
+
+		print(datetime.format(formatter))
+		[/codeblock]
 	</description>
 	<tutorials>
 	</tutorials>

doc/classes/JavaObject.xml

@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="UTF-8" ?>
+<class name="JavaObject" inherits="RefCounted" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="../class.xsd">
+	<brief_description>
+		Represents an object from the Java Native Interface.
+	</brief_description>
+	<description>
+		Represents an object from the Java Native Interface. It can be returned from Java methods called on [JavaClass] or other [JavaObject]s. See [JavaClassWrapper] for an example.
+		[b]Note:[/b] This class only works on Android. On any other platform, this class does nothing.
+		[b]Note:[/b] This class is not to be confused with [JavaScriptObject].
+	</description>
+	<tutorials>
+	</tutorials>
+	<methods>
+		<method name="get_java_class" qualifiers="const">
+			<return type="JavaClass" />
+			<description>
+				Returns the [JavaClass] that this object is an instance of.
+			</description>
+		</method>
+	</methods>
+</class>

platform/android/api/api.cpp

@@ -49,6 +49,7 @@ void register_android_api() {
 #endif
 
 	GDREGISTER_CLASS(JavaClass);
+	GDREGISTER_CLASS(JavaObject);
 	GDREGISTER_CLASS(JavaClassWrapper);
 	Engine::get_singleton()->add_singleton(Engine::Singleton("JavaClassWrapper", JavaClassWrapper::get_singleton()));
 }
@@ -59,6 +60,16 @@ void unregister_android_api() {
 #endif
 }
 
+void JavaClass::_bind_methods() {
+	ClassDB::bind_method(D_METHOD("get_java_class_name"), &JavaClass::get_java_class_name);
+	ClassDB::bind_method(D_METHOD("get_java_method_list"), &JavaClass::get_java_method_list);
+	ClassDB::bind_method(D_METHOD("get_java_parent_class"), &JavaClass::get_java_parent_class);
+}
+
+void JavaObject::_bind_methods() {
+	ClassDB::bind_method(D_METHOD("get_java_class"), &JavaObject::get_java_class);
+}
+
 void JavaClassWrapper::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("wrap", "name"), &JavaClassWrapper::wrap);
 }
@@ -69,13 +80,32 @@ Variant JavaClass::callp(const StringName &, const Variant **, int, Callable::Ca
 	return Variant();
 }
 
+String JavaClass::get_java_class_name() const {
+	return "";
+}
+
+TypedArray<Dictionary> JavaClass::get_java_method_list() const {
+	return TypedArray<Dictionary>();
+}
+
+Ref<JavaClass> JavaClass::get_java_parent_class() const {
+	return Ref<JavaClass>();
+}
+
 JavaClass::JavaClass() {
 }
 
+JavaClass::~JavaClass() {
+}
+
 Variant JavaObject::callp(const StringName &, const Variant **, int, Callable::CallError &) {
 	return Variant();
 }
 
+Ref<JavaClass> JavaObject::get_java_class() const {
+	return Ref<JavaClass>();
+}
+
 JavaClassWrapper *JavaClassWrapper::singleton = nullptr;
 
 Ref<JavaClass> JavaClassWrapper::wrap(const String &) {

platform/android/api/java_class_wrapper.h

@@ -32,6 +32,7 @@
 #define JAVA_CLASS_WRAPPER_H
 
 #include "core/object/ref_counted.h"
+#include "core/variant/typed_array.h"
 
 #ifdef ANDROID_ENABLED
 #include <android/log.h>
@@ -67,6 +68,7 @@ class JavaClass : public RefCounted {
 
 	struct MethodInfo {
 		bool _static = false;
+		bool _constructor = false;
 		Vector<uint32_t> param_types;
 		Vector<StringName> param_sigs;
 		uint32_t return_type = 0;
@@ -174,14 +176,29 @@ class JavaClass : public RefCounted {
 	bool _call_method(JavaObject *p_instance, const StringName &p_method, const Variant **p_args, int p_argcount, Callable::CallError &r_error, Variant &ret);
 
 	friend class JavaClassWrapper;
+	friend class JavaObject;
+	String java_class_name;
+	String java_constructor_name;
 	HashMap<StringName, List<MethodInfo>> methods;
 	jclass _class;
 #endif
 
+protected:
+	static void _bind_methods();
+
 public:
 	virtual Variant callp(const StringName &p_method, const Variant **p_args, int p_argcount, Callable::CallError &r_error) override;
 
+	String get_java_class_name() const;
+	TypedArray<Dictionary> get_java_method_list() const;
+	Ref<JavaClass> get_java_parent_class() const;
+
+#ifdef ANDROID_ENABLED
+	virtual String to_string() override;
+#endif
+
 	JavaClass();
+	~JavaClass();
 };
 
 class JavaObject : public RefCounted {
@@ -191,14 +208,24 @@ class JavaObject : public RefCounted {
 	Ref<JavaClass> base_class;
 	friend class JavaClass;
 
-	jobject instance;
+	jobject instance = nullptr;
 #endif
 
+protected:
+	static void _bind_methods();
+
 public:
 	virtual Variant callp(const StringName &p_method, const Variant **p_args, int p_argcount, Callable::CallError &r_error) override;
 
+	Ref<JavaClass> get_java_class() const;
+
 #ifdef ANDROID_ENABLED
-	JavaObject(const Ref<JavaClass> &p_base, jobject *p_instance);
+	virtual String to_string() override;
+
+	jobject get_instance() { return instance; }
+
+	JavaObject();
+	JavaObject(const Ref<JavaClass> &p_base, jobject p_instance);
 	~JavaObject();
 #endif
 };
@@ -209,13 +236,17 @@ class JavaClassWrapper : public Object {
 #ifdef ANDROID_ENABLED
 	RBMap<String, Ref<JavaClass>> class_cache;
 	friend class JavaClass;
-	jmethodID getDeclaredMethods;
-	jmethodID getFields;
-	jmethodID getParameterTypes;
-	jmethodID getReturnType;
-	jmethodID getModifiers;
-	jmethodID getName;
+	jmethodID Class_getDeclaredConstructors;
+	jmethodID Class_getDeclaredMethods;
+	jmethodID Class_getFields;
 	jmethodID Class_getName;
+	jmethodID Class_getSuperclass;
+	jmethodID Constructor_getParameterTypes;
+	jmethodID Constructor_getModifiers;
+	jmethodID Method_getParameterTypes;
+	jmethodID Method_getReturnType;
+	jmethodID Method_getModifiers;
+	jmethodID Method_getName;
 	jmethodID Field_getName;
 	jmethodID Field_getModifiers;
 	jmethodID Field_get;
@@ -242,6 +273,8 @@ class JavaClassWrapper : public Object {
 	Ref<JavaClass> wrap(const String &p_class);
 
 #ifdef ANDROID_ENABLED
+	Ref<JavaClass> wrap_jclass(jclass p_class);
+
 	JavaClassWrapper(jobject p_activity = nullptr);
 #else
 	JavaClassWrapper();

platform/android/api/jni_singleton.h

@@ -180,6 +180,11 @@ class JNISingleton : public Object {
 				env->DeleteLocalRef(obj);
 
 			} break;
+			case Variant::OBJECT: {
+				jobject obj = env->CallObjectMethodA(instance, E->get().method, v);
+				ret = _jobject_to_variant(env, obj);
+				env->DeleteLocalRef(obj);
+			} break;
 			default: {
 				env->PopLocalFrame(nullptr);
 				ERR_FAIL_V(Variant());