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Add DecoratorPattern annotation
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‎CHANGELOG.md‎

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## [Unreleased]
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### Added
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- Add DecoratorPattern annotation [#338](https://github.com/nbbrd/java-design-util/issues/338)
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### Fixed
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- Fix package pattern in MightBePromoted [#337](https://github.com/nbbrd/java-design-util/issues/337)

‎java-design-annotation/src/main/java/nbbrd/design/BuilderPattern.java‎

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import java.lang.annotation.*;
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/**
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* The builder pattern is a design pattern that provides a flexible solution to various object creation problems in object-oriented programming.
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* The builder pattern separates the construction of a complex object from its representation.
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*
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* @author Philippe Charles
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* @see <a href="https://en.wikipedia.org/wiki/Builder_pattern">Wikipedia</a>
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*/
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@Target({ElementType.TYPE})
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@Retention(RetentionPolicy.SOURCE)
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@Documented
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public @interface BuilderPattern {
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/**
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* The type of the object that will be built by the builder.
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*
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* @return a non-null type
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*/
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Class<?> value();
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/**
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* The name of the method that builds the object.
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*
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* @return a non-null method name
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*/
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String buildMethodName() default "build";
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}

‎java-design-annotation/src/main/java/nbbrd/design/DecoratorPattern.java‎

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package nbbrd.design;
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import java.lang.annotation.*;
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/**
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* In object-oriented programming, the decorator pattern is a design pattern that allows behavior to be added to an individual object,
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* dynamically, without affecting the behavior of other instances of the same class.
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*
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* @see <a href="https://en.wikipedia.org/wiki/Decorator_pattern">Wikipedia</a>
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*/
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@Target({ElementType.TYPE})
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@Retention(RetentionPolicy.SOURCE)
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@Documented
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public @interface DecoratorPattern {
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/**
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* The interface (or class) to decorate.<br>This
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* value is optional if the decorator implements/extends exactly one
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* interface/class.
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*
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* @return a non-null type
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*/
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Class<?> value() default Void.class;
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}

‎java-design-processor/src/main/java/internal/nbbrd/design/DecoratorPatternProcessor.java‎

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/*
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* Copyright 2018 National Bank of Belgium
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*
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* Licensed under the EUPL, Version 1.1 or - as soon they will be approved
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* by the European Commission - subsequent versions of the EUPL (the "Licence");
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* You may not use this work except in compliance with the Licence.
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* You may obtain a copy of the Licence at:
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*
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* http://ec.europa.eu/idabc/eupl
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the Licence is distributed on an "AS IS" basis,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the Licence for the specific language governing permissions and
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* limitations under the Licence.
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*/
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package internal.nbbrd.design;
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import internal.nbbrd.design.proc.Elements2;
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import internal.nbbrd.design.proc.Processing;
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import internal.nbbrd.design.proc.Processors;
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import internal.nbbrd.design.proc.Rule;
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import nbbrd.design.DecoratorPattern;
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import nbbrd.service.ServiceProvider;
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import javax.annotation.processing.*;
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import javax.lang.model.SourceVersion;
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import javax.lang.model.element.ElementKind;
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import javax.lang.model.element.TypeElement;
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import javax.lang.model.type.NoType;
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import javax.lang.model.type.TypeKind;
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import javax.lang.model.type.TypeMirror;
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import java.util.List;
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import java.util.Optional;
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import java.util.Set;
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import static internal.nbbrd.design.proc.Processors.extractResultType;
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/**
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* @author Philippe Charles
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*/
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@ServiceProvider(Processor.class)
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@SupportedAnnotationTypes("nbbrd.design.DecoratorPattern")
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public final class DecoratorPatternProcessor extends AbstractProcessor {
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@Override
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public SourceVersion getSupportedSourceVersion() {
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return SourceVersion.latestSupported();
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}
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@Override
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public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) {
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return Processing.of(IS_DECORATOR_PATTERN).process(annotations, roundEnv, processingEnv);
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}
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private static final Rule<TypeElement> IS_DECORATOR_PATTERN =
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Rule.on(TypeElement.class)
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.and(Rule.is(ElementKind.CLASS))
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.and(Rule.of(DecoratorPatternProcessor::isExtendingDecoratedType, "'%s' doesn't extend a class"))
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.and(Rule.of(DecoratorPatternProcessor::hasConstructorWithDecoratedType, "'%s' doesn't have a constructor with the decorated type"));
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private static boolean isExtendingDecoratedType(ProcessingEnvironment env, TypeElement type) {
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return getDecoratedType(env, type)
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.filter(decoratedType -> isExtendingDecoratedType(env, type, decoratedType))
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.isPresent();
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}
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private static boolean isExtendingDecoratedType(ProcessingEnvironment env, TypeElement type, TypeMirror decoratedType) {
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return env.getTypeUtils().isAssignable(type.getSuperclass(), decoratedType) ||
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type.getInterfaces().stream().anyMatch(x -> env.getTypeUtils().isAssignable(x, decoratedType));
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}
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private static boolean hasConstructorWithDecoratedType(ProcessingEnvironment env, TypeElement type) {
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return getDecoratedType(env, type)
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.filter(decoratedType -> hasConstructorWithDecoratedType(env, type, decoratedType))
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.isPresent();
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}
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private static boolean hasConstructorWithDecoratedType(ProcessingEnvironment env, TypeElement type, TypeMirror decoratedType) {
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return Elements2.constructorsIn(type)
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.flatMap(method -> method.getParameters().stream())
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.anyMatch(var -> env.getTypeUtils().isSameType(decoratedType, var.asType()));
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}
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private static boolean isNullType(ProcessingEnvironment env, TypeMirror expected) {
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return env.getTypeUtils().isSameType(Processors.getTypeMirror(env, Void.class), expected);
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}
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private static boolean isDirectSuperClass(TypeMirror found) {
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return !(found instanceof NoType && found.getKind() == TypeKind.NONE) && !(found.toString().equals("java.lang.Object"));
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}
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private static Optional<TypeMirror> inferDecoratedType(TypeElement type) {
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TypeMirror superclass = type.getSuperclass();
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List<? extends TypeMirror> parents = type.getInterfaces();
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return isDirectSuperClass(superclass) && parents.isEmpty()
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? Optional.of(superclass)
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: (!isDirectSuperClass(superclass) && parents.size() == 1 ? Optional.of(parents.get(0)) : Optional.empty());
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}
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private static Optional<TypeMirror> getDecoratedType(ProcessingEnvironment env, TypeElement type) {
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TypeMirror result = extractResultType(type.getAnnotation(DecoratorPattern.class)::value);
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return isNullType(env, result) ? inferDecoratedType(type) : Optional.of(result);
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}
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}

‎java-design-processor/src/test/java/internal/nbbrd/design/DecoratorPatternProcessorTest.java‎

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package internal.nbbrd.design;
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import com.google.testing.compile.Compilation;
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import com.google.testing.compile.JavaFileObjects;
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import org.junit.jupiter.api.Test;
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import javax.tools.JavaFileObject;
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import static com.google.testing.compile.CompilationSubject.assertThat;
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class DecoratorPatternProcessorTest {
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@Test
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public void testValid() {
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JavaFileObject file = JavaFileObjects.forResource("internal/nbbrd/design/TestDecoratorValid.java");
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Compilation compilation = compile(file);
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assertThat(compilation)
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.succeededWithoutWarnings();
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}
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@Test
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public void testConstructorMissing() {
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JavaFileObject file = JavaFileObjects.forResource("internal/nbbrd/design/TestDecoratorConstructorMissing.java");
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Compilation compilation = compile(file);
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assertThat(compilation)
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.failed();
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}
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@Test
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public void testConstructorNoArg() {
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JavaFileObject file = JavaFileObjects.forResource("internal/nbbrd/design/TestDecoratorConstructorNoArg.java");
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Compilation compilation = compile(file);
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assertThat(compilation)
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.failed();
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}
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@Test
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public void testConstructorNoDecorated() {
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JavaFileObject file = JavaFileObjects.forResource("internal/nbbrd/design/TestDecoratorConstructorNoDecorated.java");
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Compilation compilation = compile(file);
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assertThat(compilation)
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.failed();
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}
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@Test
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public void testConstructorSuper() {
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JavaFileObject file = JavaFileObjects.forResource("internal/nbbrd/design/TestDecoratorConstructorSuper.java");
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Compilation compilation = compile(file);
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assertThat(compilation)
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.failed();
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}
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private Compilation compile(JavaFileObject file) {
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return com.google.testing.compile.Compiler.javac()
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.withProcessors(new DecoratorPatternProcessor())
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.compile(file);
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}
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}

‎java-design-processor/src/test/resources/internal/nbbrd/design/TestDecoratorConstructorMissing.java‎

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package internal.nbbrd.design;
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import nbbrd.design.DecoratorPattern;
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import java.io.Reader;
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@DecoratorPattern
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public abstract class TestDecoratorConstructorMissing extends Reader {
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}

‎java-design-processor/src/test/resources/internal/nbbrd/design/TestDecoratorConstructorNoArg.java‎

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package internal.nbbrd.design;
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import nbbrd.design.DecoratorPattern;
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import java.io.Reader;
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@DecoratorPattern
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public abstract class TestDecoratorConstructorNoArg extends Reader {
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TestDecoratorConstructorNoArg() {}
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}

‎java-design-processor/src/test/resources/internal/nbbrd/design/TestDecoratorConstructorNoDecorated.java‎

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package internal.nbbrd.design;
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import nbbrd.design.DecoratorPattern;
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import java.io.Reader;
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@DecoratorPattern
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public abstract class TestDecoratorConstructorNoDecorated extends Reader {
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TestDecoratorConstructorNoDecorated(boolean stuff) {}
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}

‎java-design-processor/src/test/resources/internal/nbbrd/design/TestDecoratorConstructorSuper.java‎

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package internal.nbbrd.design;
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import nbbrd.design.DecoratorPattern;
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import java.io.FilterInputStream;
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import java.io.InputStream;
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import java.io.Reader;
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@DecoratorPattern
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public abstract class TestDecoratorConstructorSuper extends FilterInputStream {
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TestDecoratorConstructorSuper(InputStream delegate) { super(delegate); }
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}

‎java-design-processor/src/test/resources/internal/nbbrd/design/TestDecoratorValid.java‎

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package internal.nbbrd.design;
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import nbbrd.design.DecoratorPattern;
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import java.io.*;
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public class TestDecoratorValid {
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@DecoratorPattern
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public abstract static class V1 extends Reader {
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V1(Reader delegate) {}
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}
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@DecoratorPattern
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public abstract static class V2 implements Closeable {
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V2(Closeable delegate) {}
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}
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@DecoratorPattern(Closeable.class)
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public abstract static class V3 extends Reader implements Closeable, Flushable {
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V3(Closeable delegate) {}
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}
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@DecoratorPattern
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public abstract static class V4 implements Closeable {
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V4(boolean stuff, Closeable delegate) {}
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}
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@DecoratorPattern(InputStream.class)
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public abstract static class V5 extends FilterInputStream {
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V5(InputStream delegate) { super(delegate); }
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}
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}

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