Native Libraries: moved code to JNIUtils.cpp and *MessageDialog.cpp

flatlaf-natives/flatlaf-natives-linux/src/main/cpp/GtkFileChooser.cpp

@@ -19,6 +19,7 @@
 #include <gtk/gtk.h>
 #include <gdk/gdkx.h>
 #include <glib/gi18n.h>
+#include "JNIUtils.h"
 #include "com_formdev_flatlaf_ui_FlatNativeLinuxLibrary.h"
 
 /**
@@ -32,26 +33,6 @@ extern Window getWindowHandle( JNIEnv* env, JAWT* awt, jobject window, Display**
 // declare internal methods
 static jobjectArray fileListToStringArray( JNIEnv* env, GSList* fileList );
 
-//---- class AutoReleaseStringUTF8 --------------------------------------------
-
-class AutoReleaseStringUTF8 {
-	JNIEnv* env;
-	jstring javaString;
-	const char* chars;
-
-public:
-	AutoReleaseStringUTF8( JNIEnv* _env, jstring _javaString ) {
-		env = _env;
-		javaString = _javaString;
-		chars = (javaString != NULL) ? env->GetStringUTFChars( javaString, NULL ) : NULL;
-	}
-	~AutoReleaseStringUTF8() {
-		if( chars != NULL )
-			env->ReleaseStringUTFChars( javaString, chars );
-	}
-	operator const gchar*() { return chars; }
-};
-
 //---- helper -----------------------------------------------------------------
 
 #define isOptionSet( option ) ((optionsSet & com_formdev_flatlaf_ui_FlatNativeLinuxLibrary_ ## option) != 0)
@@ -293,52 +274,3 @@ static jobjectArray fileListToStringArray( JNIEnv* env, GSList* fileList ) {
 	g_slist_free( fileList );
 	return array;
 }
-
-
-extern "C"
-JNIEXPORT jint JNICALL Java_com_formdev_flatlaf_ui_FlatNativeLinuxLibrary_showMessageDialog
-	( JNIEnv* env, jclass cls, jlong hwndParent, jint messageType, jstring primaryText, jstring secondaryText,
-		jint defaultButton, jobjectArray buttons )
-{
-	GtkWindow* window = (GtkWindow*) hwndParent;
-
-	// convert message type
-	GtkMessageType gmessageType;
-	switch( messageType ) {
-		case /* JOptionPane.ERROR_MESSAGE */       0: gmessageType = GTK_MESSAGE_ERROR; break;
-		case /* JOptionPane.INFORMATION_MESSAGE */ 1: gmessageType = GTK_MESSAGE_INFO; break;
-		case /* JOptionPane.WARNING_MESSAGE */     2: gmessageType = GTK_MESSAGE_WARNING; break;
-		case /* JOptionPane.QUESTION_MESSAGE */    3: gmessageType = GTK_MESSAGE_QUESTION; break;
-		default:
-		case /* JOptionPane.PLAIN_MESSAGE */      -1: gmessageType = GTK_MESSAGE_OTHER; break;
-	}
-
-	// convert Java strings to C strings
-	AutoReleaseStringUTF8 cprimaryText( env, primaryText );
-	AutoReleaseStringUTF8 csecondaryText( env, secondaryText );
-
-	// create GTK file chooser dialog
-	// https://docs.gtk.org/gtk3/class.MessageDialog.html
-	jint buttonCount = env->GetArrayLength( buttons );
-	GtkWidget* dialog = gtk_message_dialog_new( window, GTK_DIALOG_MODAL, gmessageType,
-		(buttonCount > 0) ? GTK_BUTTONS_NONE : GTK_BUTTONS_OK,
-		"%s", (const gchar*) cprimaryText );
-	if( csecondaryText != NULL )
-		gtk_message_dialog_format_secondary_text( GTK_MESSAGE_DIALOG( dialog ), "%s", (const gchar*) csecondaryText );
-
-	// add buttons
-	for( int i = 0; i < buttonCount; i++ ) {
-		AutoReleaseStringUTF8 str( env, (jstring) env->GetObjectArrayElement( buttons, i ) );
-		gtk_dialog_add_button( GTK_DIALOG( dialog ), str, i );
-	}
-
-	// set default button
-	gtk_dialog_set_default_response( GTK_DIALOG( dialog ), MIN( MAX( defaultButton, 0 ), buttonCount - 1 ) );
-
-	// show message dialog
-	gint responseID = gtk_dialog_run( GTK_DIALOG( dialog ) );
-	gtk_widget_destroy( dialog );
-
-	// return -1 if closed with ESC key
-	return (responseID >= 0) ? responseID : -1;
-}

flatlaf-natives/flatlaf-natives-linux/src/main/cpp/GtkMessageDialog.cpp

@@ -0,0 +1,76 @@
+/*
+ * Copyright 2025 FormDev Software GmbH
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <jawt.h>
+#include <linux/jawt_md.h>
+#include <gtk/gtk.h>
+#include <gdk/gdkx.h>
+#include <glib/gi18n.h>
+#include "JNIUtils.h"
+#include "com_formdev_flatlaf_ui_FlatNativeLinuxLibrary.h"
+
+/**
+ * @author Karl Tauber
+ * @since 3.6
+ */
+
+extern "C"
+JNIEXPORT jint JNICALL Java_com_formdev_flatlaf_ui_FlatNativeLinuxLibrary_showMessageDialog
+	( JNIEnv* env, jclass cls, jlong hwndParent, jint messageType, jstring primaryText, jstring secondaryText,
+		jint defaultButton, jobjectArray buttons )
+{
+	GtkWindow* window = (GtkWindow*) hwndParent;
+
+	// convert message type
+	GtkMessageType gmessageType;
+	switch( messageType ) {
+		case /* JOptionPane.ERROR_MESSAGE */       0: gmessageType = GTK_MESSAGE_ERROR; break;
+		case /* JOptionPane.INFORMATION_MESSAGE */ 1: gmessageType = GTK_MESSAGE_INFO; break;
+		case /* JOptionPane.WARNING_MESSAGE */     2: gmessageType = GTK_MESSAGE_WARNING; break;
+		case /* JOptionPane.QUESTION_MESSAGE */    3: gmessageType = GTK_MESSAGE_QUESTION; break;
+		default:
+		case /* JOptionPane.PLAIN_MESSAGE */      -1: gmessageType = GTK_MESSAGE_OTHER; break;
+	}
+
+	// convert Java strings to C strings
+	AutoReleaseStringUTF8 cprimaryText( env, primaryText );
+	AutoReleaseStringUTF8 csecondaryText( env, secondaryText );
+
+	// create GTK file chooser dialog
+	// https://docs.gtk.org/gtk3/class.MessageDialog.html
+	jint buttonCount = env->GetArrayLength( buttons );
+	GtkWidget* dialog = gtk_message_dialog_new( window, GTK_DIALOG_MODAL, gmessageType,
+		(buttonCount > 0) ? GTK_BUTTONS_NONE : GTK_BUTTONS_OK,
+		"%s", (const gchar*) cprimaryText );
+	if( csecondaryText != NULL )
+		gtk_message_dialog_format_secondary_text( GTK_MESSAGE_DIALOG( dialog ), "%s", (const gchar*) csecondaryText );
+
+	// add buttons
+	for( int i = 0; i < buttonCount; i++ ) {
+		AutoReleaseStringUTF8 str( env, (jstring) env->GetObjectArrayElement( buttons, i ) );
+		gtk_dialog_add_button( GTK_DIALOG( dialog ), str, i );
+	}
+
+	// set default button
+	gtk_dialog_set_default_response( GTK_DIALOG( dialog ), MIN( MAX( defaultButton, 0 ), buttonCount - 1 ) );
+
+	// show message dialog
+	gint responseID = gtk_dialog_run( GTK_DIALOG( dialog ) );
+	gtk_widget_destroy( dialog );
+
+	// return -1 if closed with ESC key
+	return (responseID >= 0) ? responseID : -1;
+}

flatlaf-natives/flatlaf-natives-linux/src/main/cpp/JNIUtils.cpp

@@ -0,0 +1,37 @@
+/*
+ * Copyright 2024 FormDev Software GmbH
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+// avoid inlining of printf()
+#define _NO_CRT_STDIO_INLINE
+
+#include "JNIUtils.h"
+
+/**
+ * @author Karl Tauber
+ */
+
+//---- class AutoReleaseStringUTF8 --------------------------------------------
+
+AutoReleaseStringUTF8::AutoReleaseStringUTF8( JNIEnv* _env, jstring _javaString ) {
+	env = _env;
+	javaString = _javaString;
+	chars = (javaString != NULL) ? env->GetStringUTFChars( javaString, NULL ) : NULL;
+}
+
+AutoReleaseStringUTF8::~AutoReleaseStringUTF8() {
+	if( chars != NULL )
+		env->ReleaseStringUTFChars( javaString, chars );
+}

flatlaf-natives/flatlaf-natives-linux/src/main/headers/JNIUtils.h

@@ -0,0 +1,36 @@
+/*
+ * Copyright 2025 FormDev Software GmbH
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <gtk/gtk.h>
+#include <jni.h>
+
+/**
+ * @author Karl Tauber
+ */
+
+//---- class AutoReleaseStringUTF8 --------------------------------------------
+
+class AutoReleaseStringUTF8 {
+	JNIEnv* env;
+	jstring javaString;
+	const char* chars;
+
+public:
+	AutoReleaseStringUTF8( JNIEnv* _env, jstring _javaString );
+	~AutoReleaseStringUTF8();
+
+	operator const gchar*() { return chars; }
+};

flatlaf-natives/flatlaf-natives-macos/src/main/objcpp/MacFileChooser.mm

@@ -366,61 +366,3 @@ static jobjectArray urlsToStringArray( JNIEnv* env, NSArray* urls ) {
 	}
 	return array;
 }
-
-extern "C"
-JNIEXPORT jint JNICALL Java_com_formdev_flatlaf_ui_FlatNativeMacLibrary_showMessageDialog
-	( JNIEnv* env, jclass cls, jlong hwndParent, jint alertStyle, jstring messageText, jstring informativeText,
-		jint defaultButton, jobjectArray buttons )
-{
-	JNI_COCOA_ENTER()
-
-	// convert Java strings to NSString (on Java thread)
-	NSString* nsMessageText = JavaToNSString( env, messageText );
-	NSString* nsInformativeText = JavaToNSString( env, informativeText );
-
-	jint buttonCount = env->GetArrayLength( buttons );
-	NSMutableArray* nsButtons = [NSMutableArray array];
-	for( int i = 0; i < buttonCount; i++ ) {
-		NSString* nsButton = JavaToNSString( env, (jstring) env->GetObjectArrayElement( buttons, i ) );
-		[nsButtons addObject:nsButton];
-	}
-
-	jint result = -1;
-	jint* presult = &result;
-
-	// show alert on macOS thread
-	[FlatJNFRunLoop performOnMainThreadWaiting:YES withBlock:^(){
-		NSAlert* alert = [[NSAlert alloc] init];
-
-		// use empty string because if alert.messageText is not set it displays "Alert"
-		alert.messageText = (nsMessageText != NULL) ? nsMessageText : @"";
-		if( nsInformativeText != NULL )
-			alert.informativeText = nsInformativeText;
-
-		// alert style
-		switch( alertStyle ) {
-			case /* JOptionPane.ERROR_MESSAGE */       0: alert.alertStyle = NSAlertStyleCritical; break;
-			default:
-			case /* JOptionPane.INFORMATION_MESSAGE */ 1: alert.alertStyle = NSAlertStyleInformational; break;
-			case /* JOptionPane.WARNING_MESSAGE */     2: alert.alertStyle = NSAlertStyleWarning; break;
-		}
-
-		// add buttons
-		for( int i = 0; i < nsButtons.count; i++ ) {
-			NSButton* b = [alert addButtonWithTitle:nsButtons[i]];
-			if( i == defaultButton )
-				alert.window.defaultButtonCell = b.cell;
-		}
-
-		// show alert
-		NSInteger response = [alert runModal];
-
-		// if no buttons added, which shows a single OK button, the response is 0 when clicking OK
-		// if buttons added, response is 1000+buttonIndex
-		*presult = MAX( response - NSAlertFirstButtonReturn, 0 );
-	}];
-
-	return result;
-
-	JNI_COCOA_EXIT()
-}

flatlaf-natives/flatlaf-natives-macos/src/main/objcpp/MacMessageDialog.mm

@@ -0,0 +1,85 @@
+/*
+ * Copyright 2024 FormDev Software GmbH
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#import <Cocoa/Cocoa.h>
+#import <objc/runtime.h>
+#import <jni.h>
+#import "JNIUtils.h"
+#import "JNFRunLoop.h"
+#import "com_formdev_flatlaf_ui_FlatNativeMacLibrary.h"
+
+/**
+ * @author Karl Tauber
+ * @since 3.6
+ */
+
+extern "C"
+JNIEXPORT jint JNICALL Java_com_formdev_flatlaf_ui_FlatNativeMacLibrary_showMessageDialog
+	( JNIEnv* env, jclass cls, jlong hwndParent, jint alertStyle, jstring messageText, jstring informativeText,
+		jint defaultButton, jobjectArray buttons )
+{
+	JNI_COCOA_ENTER()
+
+	// convert Java strings to NSString (on Java thread)
+	NSString* nsMessageText = JavaToNSString( env, messageText );
+	NSString* nsInformativeText = JavaToNSString( env, informativeText );
+
+	jint buttonCount = env->GetArrayLength( buttons );
+	NSMutableArray* nsButtons = [NSMutableArray array];
+	for( int i = 0; i < buttonCount; i++ ) {
+		NSString* nsButton = JavaToNSString( env, (jstring) env->GetObjectArrayElement( buttons, i ) );
+		[nsButtons addObject:nsButton];
+	}
+
+	jint result = -1;
+	jint* presult = &result;
+
+	// show alert on macOS thread
+	[FlatJNFRunLoop performOnMainThreadWaiting:YES withBlock:^(){
+		NSAlert* alert = [[NSAlert alloc] init];
+
+		// use empty string because if alert.messageText is not set it displays "Alert"
+		alert.messageText = (nsMessageText != NULL) ? nsMessageText : @"";
+		if( nsInformativeText != NULL )
+			alert.informativeText = nsInformativeText;
+
+		// alert style
+		switch( alertStyle ) {
+			case /* JOptionPane.ERROR_MESSAGE */       0: alert.alertStyle = NSAlertStyleCritical; break;
+			default:
+			case /* JOptionPane.INFORMATION_MESSAGE */ 1: alert.alertStyle = NSAlertStyleInformational; break;
+			case /* JOptionPane.WARNING_MESSAGE */     2: alert.alertStyle = NSAlertStyleWarning; break;
+		}
+
+		// add buttons
+		for( int i = 0; i < nsButtons.count; i++ ) {
+			NSButton* b = [alert addButtonWithTitle:nsButtons[i]];
+			if( i == defaultButton )
+				alert.window.defaultButtonCell = b.cell;
+		}
+
+		// show alert
+		NSInteger response = [alert runModal];
+
+		// if no buttons added, which shows a single OK button, the response is 0 when clicking OK
+		// if buttons added, response is 1000+buttonIndex
+		*presult = MAX( response - NSAlertFirstButtonReturn, 0 );
+	}];
+
+	return result;
+
+	JNI_COCOA_EXIT()
+}

flatlaf-natives/flatlaf-natives-windows/src/main/cpp/JNIUtils.cpp

@@ -0,0 +1,67 @@
+/*
+ * Copyright 2024 FormDev Software GmbH
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+// avoid inlining of printf()
+#define _NO_CRT_STDIO_INLINE
+
+#include "JNIUtils.h"
+
+/**
+ * @author Karl Tauber
+ */
+
+//---- class AutoReleaseString ------------------------------------------------
+
+AutoReleaseString::AutoReleaseString( JNIEnv* _env, jstring _javaString ) {
+	env = _env;
+	javaString = _javaString;
+	chars = (javaString != NULL) ? env->GetStringChars( javaString, NULL ) : NULL;
+}
+
+AutoReleaseString::~AutoReleaseString() {
+	if( chars != NULL )
+		env->ReleaseStringChars( javaString, chars );
+}
+
+//---- class AutoReleaseStringArray -------------------------------------------
+
+AutoReleaseStringArray::AutoReleaseStringArray( JNIEnv* _env, jobjectArray _javaStringArray ) {
+	env = _env;
+	count = (_javaStringArray != NULL) ? env->GetArrayLength( _javaStringArray ) : 0;
+	if( count <= 0 )
+		return;
+
+	javaStringArray = new jstring[count];
+	charsArray = new const jchar*[count];
+
+	for( int i = 0; i < count; i++ ) {
+		javaStringArray[i] = (jstring) env->GetObjectArrayElement( _javaStringArray, i );
+		charsArray[i] = env->GetStringChars( javaStringArray[i] , NULL );
+	}
+}
+
+AutoReleaseStringArray::~AutoReleaseStringArray() {
+	if( count == 0 )
+		return;
+
+	for( int i = 0; i < count; i++ ) {
+		env->ReleaseStringChars( javaStringArray[i], charsArray[i] );
+		env->DeleteLocalRef( javaStringArray[i] );
+	}
+
+	delete[] javaStringArray;
+	delete[] charsArray;
+}

flatlaf-natives/flatlaf-natives-windows/src/main/cpp/WinFileChooser.cpp

@@ -19,6 +19,7 @@
 
 #include <windows.h>
 #include <shobjidl.h>
+#include "JNIUtils.h"
 #include "com_formdev_flatlaf_ui_FlatNativeWindowsLibrary.h"
 
 /**
@@ -54,26 +55,6 @@ public:
 	operator T*() { return ptr; }
 };
 
-//---- class AutoReleaseString ------------------------------------------------
-
-class AutoReleaseString {
-	JNIEnv* env;
-	jstring javaString;
-	const jchar* chars;
-
-public:
-	AutoReleaseString( JNIEnv* _env, jstring _javaString ) {
-		env = _env;
-		javaString = _javaString;
-		chars = (javaString != NULL) ? env->GetStringChars( javaString, NULL ) : NULL;
-	}
-	~AutoReleaseString() {
-		if( chars != NULL )
-			env->ReleaseStringChars( javaString, chars );
-	}
-	operator LPCWSTR() { return (LPCWSTR) chars; }
-};
-
 //---- class AutoReleaseIShellItem --------------------------------------------
 
 class AutoReleaseIShellItem : public AutoReleasePtr<IShellItem> {
@@ -87,48 +68,29 @@ public:
 //---- class FilterSpec -------------------------------------------------------
 
 class FilterSpec {
-	JNIEnv* env = NULL;
-	jstring* jnames = NULL;
-	jstring* jspecs = NULL;
+	AutoReleaseStringArray fileTypes;
 
 public:
 	UINT count = 0;
 	COMDLG_FILTERSPEC* specs = NULL;
 
 public:
-	FilterSpec( JNIEnv* _env, jobjectArray fileTypes ) {
-		if( fileTypes == NULL )
+	FilterSpec( JNIEnv* _env, jobjectArray _fileTypes )
+		: fileTypes( _env, _fileTypes )
+	{
+		if( fileTypes.count == 0 )
 			return;
 
-		env = _env;
-		count = env->GetArrayLength( fileTypes ) / 2;
-		if( count <= 0 )
-			return;
-
-		specs = new COMDLG_FILTERSPEC[count];
-		jnames = new jstring[count];
-		jspecs = new jstring[count];
+		count = fileTypes.count / 2;
+		specs = new COMDLG_FILTERSPEC[fileTypes.count];
 
 		for( int i = 0; i < count; i++ ) {
-			jnames[i] = (jstring) env->GetObjectArrayElement( fileTypes, i * 2 );
-			jspecs[i] = (jstring) env->GetObjectArrayElement( fileTypes, (i * 2) + 1 );
-			specs[i].pszName = (LPCWSTR) env->GetStringChars( jnames[i] , NULL );
-			specs[i].pszSpec = (LPCWSTR) env->GetStringChars( jspecs[i], NULL );
+			specs[i].pszName = fileTypes[i * 2];
+			specs[i].pszSpec = fileTypes[(i * 2) + 1];
 		}
 	}
 	~FilterSpec() {
-		if( specs == NULL )
-			return;
-
-		for( int i = 0; i < count; i++ ) {
-			env->ReleaseStringChars( jnames[i], (jchar *) specs[i].pszName );
-			env->ReleaseStringChars( jspecs[i], (jchar *) specs[i].pszSpec );
-			env->DeleteLocalRef( jnames[i] );
-			env->DeleteLocalRef( jspecs[i] );
-		}
-
-		delete[] jnames;
-		delete[] jspecs;
+		if( specs != NULL )
 			delete[] specs;
 	}
 };
@@ -369,15 +331,3 @@ static jobjectArray getFiles( JNIEnv* env, jboolean open, IFileDialog* dialog )
 		return array;
 	}
 }
-
-
-extern "C"
-JNIEXPORT jint JNICALL Java_com_formdev_flatlaf_ui_FlatNativeWindowsLibrary_showMessageDialog
-	( JNIEnv* env, jclass cls, jlong hwndParent, jstring text, jstring caption, jint type )
-{
-	// convert Java strings to C strings
-	AutoReleaseString ctext( env, text );
-	AutoReleaseString ccaption( env, caption );
-
-	return ::MessageBox( reinterpret_cast<HWND>( hwndParent ), ctext, ccaption, type );
-}

flatlaf-natives/flatlaf-natives-windows/src/main/cpp/WinMessageDialog.cpp

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2024 FormDev Software GmbH
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+// avoid inlining of printf()
+#define _NO_CRT_STDIO_INLINE
+
+#include <windows.h>
+#include "JNIUtils.h"
+#include "com_formdev_flatlaf_ui_FlatNativeWindowsLibrary.h"
+
+/**
+ * @author Karl Tauber
+ * @since 3.6
+ */
+
+extern "C"
+JNIEXPORT jint JNICALL Java_com_formdev_flatlaf_ui_FlatNativeWindowsLibrary_showMessageDialog
+	( JNIEnv* env, jclass cls, jlong hwndParent, jstring text, jstring caption, jint type )
+{
+	// convert Java strings to C strings
+	AutoReleaseString ctext( env, text );
+	AutoReleaseString ccaption( env, caption );
+
+	return ::MessageBox( reinterpret_cast<HWND>( hwndParent ), ctext, ccaption, type );
+}

flatlaf-natives/flatlaf-natives-windows/src/main/headers/JNIUtils.h

@@ -0,0 +1,53 @@
+/*
+ * Copyright 2025 FormDev Software GmbH
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <windows.h>
+#include <jni.h>
+
+/**
+ * @author Karl Tauber
+ */
+
+//---- class AutoReleaseString ------------------------------------------------
+
+class AutoReleaseString {
+	JNIEnv* env;
+	jstring javaString;
+	const jchar* chars;
+
+public:
+	AutoReleaseString( JNIEnv* _env, jstring _javaString );
+	~AutoReleaseString();
+
+	operator LPCWSTR() { return (LPCWSTR) chars; }
+};
+
+//---- class AutoReleaseStringArray -------------------------------------------
+
+class AutoReleaseStringArray {
+	JNIEnv* env;
+	jstring* javaStringArray;
+	const jchar** charsArray;
+
+public:
+	UINT count;
+
+public:
+	AutoReleaseStringArray( JNIEnv* _env, jobjectArray _javaStringArray );
+	~AutoReleaseStringArray();
+
+	operator LPCWSTR*() { return (LPCWSTR*) charsArray; }
+};