support Java Platform Module System (JPMS) (issue #1)

flatlaf-core/build.gradle.kts

@@ -26,7 +26,20 @@ repositories {
 	jcenter()
 }
 
+if( JavaVersion.current() >= JavaVersion.VERSION_1_9 ) {
+	sourceSets {
+		create( "main9" ) {
+			java {
+				setSrcDirs( listOf( "src/main9/java" ) )
+			}
+		}
+	}
+}
+
 dependencies {
+	if( JavaVersion.current() >= JavaVersion.VERSION_1_9 )
+		"main9Implementation"( files( sourceSets["main"].output.classesDirs ).builtBy( "compileJava" ) )
+
 	testImplementation( "com.miglayout:miglayout-swing:5.2" )
 	testImplementation( "com.jgoodies:jgoodies-forms:1.9.0" )
 }
@@ -37,8 +50,30 @@ java {
 }
 
 tasks {
+	if( JavaVersion.current() >= JavaVersion.VERSION_1_9 ) {
+		named<JavaCompile>( "compileMain9Java" ) {
+			doFirst {
+				options.compilerArgs = listOf(
+					"--release", "9",
+					"--patch-module", "com.formdev.flatlaf=" + classpath.asPath
+				)
+				classpath = files()
+			}
+		}
+	}
+	
 	jar {
 		archiveBaseName.set( "flatlaf" )
+
+		if( JavaVersion.current() >= JavaVersion.VERSION_1_9 ) {
+			manifest.attributes(
+				"Multi-Release" to "true"
+			)
+
+			into( "META-INF/versions/9" ) {
+				from( sourceSets["main9"].output )
+			}
+		}
 	}
 
 	javadoc {

flatlaf-core/src/main9/java/module-info.java

@@ -0,0 +1,27 @@
+/*
+ * Copyright 2019 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
+ *
+ *     http://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.
+ */
+
+/**
+ * @author Karl Tauber
+ */
+module com.formdev.flatlaf {
+	requires java.desktop;
+
+	exports com.formdev.flatlaf;
+	exports com.formdev.flatlaf.icons;
+	exports com.formdev.flatlaf.ui;
+	exports com.formdev.flatlaf.util;
+}