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[J17] Add intermodule class loading example
Manual Loading: Few Modules (Separately - wtih deps).
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‎java-17/manual/few-modules/separately/with-deps/dependency/build.gradle

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plugins {
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id 'java-library'
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}
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group = 'com.habr.j17.manual.fewmodules.separately.nodeps.dependency'
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version = '1.0'
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compileJava {
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java {
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toolchain {
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languageVersion = JavaLanguageVersion.of(17)
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}
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}
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}
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sourceSets {
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main.java.srcDirs = ['src']
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}

‎java-17/manual/few-modules/separately/with-deps/dependency/src/com/habr/j17/manual/fewmodules/separately/withdeps/dependency/Dog.java

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package com.habr.j17.manual.fewmodules.separately.withdeps.dependency;
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public class Dog {
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public void talk() {
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System.out.println("Woof");
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}
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}

‎java-17/manual/few-modules/separately/with-deps/dependency/src/module-info.java

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module manual.fewmodules.separately.withdeps.dependency {
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exports com.habr.j17.manual.fewmodules.separately.withdeps.dependency;
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}

‎java-17/manual/few-modules/separately/with-deps/loadable/build.gradle

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plugins {
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id 'java'
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id 'application'
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}
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group = 'com.habr.j17.manual.fewmodules.separately.withdeps.loadable'
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version = '1.0'
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compileJava {
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java {
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toolchain {
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languageVersion = JavaLanguageVersion.of(17)
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}
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}
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}
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application {
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mainClassName = 'com.habr.j17.manual.fewmodules.separately.withdeps.loadable.Main'
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}
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dependencies {
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implementation project(":java-17:manual:few-modules:separately:with-deps:dependency")
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}
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sourceSets {
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main.java.srcDirs = ['src']
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}
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jar {
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manifest {
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attributes(
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"Main-Class": application.mainClass
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)
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}
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}

‎java-17/manual/few-modules/separately/with-deps/loadable/src/com/habr/j17/manual/fewmodules/separately/withdeps/loadable/Cat.java

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package com.habr.j17.manual.fewmodules.separately.withdeps.loadable;
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public class Cat {
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public void talk() {
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System.out.println("Meow");
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}
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}

‎java-17/manual/few-modules/separately/with-deps/loadable/src/com/habr/j17/manual/fewmodules/separately/withdeps/loadable/Main.java

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package com.habr.j17.manual.fewmodules.separately.withdeps.loadable;
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import com.habr.j17.manual.fewmodules.separately.withdeps.dependency.Dog;
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public class Main {
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public static void main(String[] args) {
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Cat cat = new Cat();
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Dog dog = new Dog();
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System.out.println("[loadable] Main Class ClassLoader is " + Main.class.getClassLoader());
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System.out.println("[loadable] Cat Class ClassLoader is " + Cat.class.getClassLoader());
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System.out.println("[dependency] Dog Class ClassLoader is " + Dog.class.getClassLoader());
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System.out.println("[loadable] Main Class Module is " + Main.class.getModule());
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System.out.println("[loadable] Cat Class Module is " + Cat.class.getModule());
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System.out.println("[dependency] Dog Class Module is " + Dog.class.getModule());
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cat.talk();
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dog.talk();
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}
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}

‎java-17/manual/few-modules/separately/with-deps/loadable/src/module-info.java

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module manual.fewmodules.separately.withdeps.loadable {
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requires manual.fewmodules.separately.withdeps.dependency;
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exports com.habr.j17.manual.fewmodules.separately.withdeps.loadable;
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}

‎java-17/manual/few-modules/separately/with-deps/loading/build.gradle

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plugins {
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id 'java'
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id 'application'
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}
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group = 'com.habr.j17.manual.fewmodules.separately.withdeps.loading'
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version = '1.0'
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compileJava {
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java {
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toolchain {
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languageVersion = JavaLanguageVersion.of(17)
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}
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}
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}
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application {
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mainClassName = 'com.habr.j17.manual.fewmodules.separately.withdeps.loading.Main'
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}
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sourceSets {
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main.java.srcDirs = ['src']
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}
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jar {
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manifest {
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attributes(
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"Main-Class": application.mainClass
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)
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}
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}

‎java-17/manual/few-modules/separately/with-deps/loading/src/com/habr/j17/manual/fewmodules/separately/withdeps/loading/CustomClassLoader.java

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package com.habr.j17.manual.fewmodules.separately.withdeps.loading;
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import java.io.File;
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import java.io.IOException;
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import java.io.InputStream;
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public class CustomClassLoader extends ClassLoader {
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private final String PKG_PREFIX = "com.habr";
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@Override
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public Class<?> loadClass(String name) throws ClassNotFoundException {
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Class<?> c = findLoadedClass(name);
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if (c != null)
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return c;
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if (name.startsWith(PKG_PREFIX)) {
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c = findClass(name);
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if (c != null) {
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System.out.println("CCL: Loading " + name);
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return c;
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}
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}
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System.out.println("CCL: Delegating " + name);
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return super.loadClass(name);
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}
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@Override
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protected Class<?> findClass(String name) throws ClassNotFoundException {
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String classFile = name.replace('.', File.separatorChar) + ".class";
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System.out.println("CCL: Finding " + name);
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try (InputStream inputStream = getResourceAsStream(classFile)) {
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if (inputStream == null)
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throw new ClassNotFoundException();
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byte[] bytecode = inputStream.readAllBytes();
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return defineClass(name, bytecode, 0, bytecode.length);
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} catch (IOException e) {
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throw new ClassNotFoundException();
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}
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}
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}

‎java-17/manual/few-modules/separately/with-deps/loading/src/com/habr/j17/manual/fewmodules/separately/withdeps/loading/Main.java

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package com.habr.j17.manual.fewmodules.separately.withdeps.loading;
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import java.lang.module.Configuration;
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import java.lang.module.ModuleFinder;
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import java.lang.reflect.Method;
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import java.nio.file.Path;
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import java.nio.file.Paths;
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import java.util.Set;
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public class Main {
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public static void main(String[] args) {
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try {
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Path loadableModulePath = Paths.get("../../../loadable/build/libs/loadable-1.0.jar");
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String loadableModuleName = "manual.fewmodules.separately.withdeps.loadable";
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Path dependencyModulePath = Paths.get("../../../dependency/build/libs/dependency-1.0.jar");
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String dependencyModuleName = "manual.fewmodules.separately.withdeps.dependency";
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String mainClassName = "com.habr.j17.manual.fewmodules.separately.withdeps.loadable.Main";
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ModuleLayer layer = createLayer(
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loadableModulePath, loadableModuleName,
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dependencyModulePath, dependencyModuleName
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);
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ClassLoader loadableCL = layer.findLoader(loadableModuleName);
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Class<?> mainClass = loadableCL.loadClass(mainClassName);
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System.out.println("[loading] Main Class Module is " + Main.class.getModule());
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System.out.println("[loading] Main Class ClassLoader is " + Main.class.getClassLoader());
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System.out.println("ClassLoader for [loadable] module is " + loadableCL);
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Method mainMethod = mainClass.getMethod("main", String[].class);
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mainMethod.invoke(null, (Object) args);
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} catch (Exception e) {
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throw new RuntimeException(e);
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}
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}
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private static ModuleLayer createLayer(Path mp1, String mn1, Path mp2, String mn2) {
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ModuleFinder finder = ModuleFinder.of(mp1, mp2);
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ModuleLayer bootLayer = ModuleLayer.boot();
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Configuration parentConfig = bootLayer.configuration();
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Configuration config = parentConfig.resolve(finder, ModuleFinder.of(), Set.of(mn1, mn2));
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return bootLayer.defineModulesWithOneLoader(config, new CustomClassLoader());
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}
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}

‎java-17/manual/few-modules/separately/with-deps/loading/src/module-info.java

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module manual.fewmodules.separately.withdeps.loading {
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}

‎settings.gradle

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include 'java-17:manual:few-modules:separately:no-deps-hack:loading'
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include 'java-17:manual:few-modules:separately:no-deps-hack:loadable'
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include 'java-17:manual:few-modules:separately:with-deps:loading'
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include 'java-17:manual:few-modules:separately:with-deps:loadable'
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include 'java-17:manual:few-modules:separately:with-deps:dependency'
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include 'java-17:auto:one-module:java8style'
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include 'java-17:auto:one-module:java17style'
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