Java tutorial
/* * Copyright (c) 2005, 2019, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package javax.lang.model.util; import java.util.ArrayList; import java.util.Collections; import java.util.List; import java.util.Map; import java.util.Set; import java.util.LinkedHashSet; import javax.lang.model.AnnotatedConstruct; import javax.lang.model.element.*; /** * Utility methods for operating on program elements. * * <p><b>Compatibility Note:</b> Methods may be added to this interface * in future releases of the platform. * * @author Joseph D. Darcy * @author Scott Seligman * @author Peter von der Ahé * @see javax.annotation.processing.ProcessingEnvironment#getElementUtils * @since 1.6 */ public interface Elements { /** * Returns a package given its fully qualified name if the package is unique in the environment. * If running with modules, all modules in the modules graph are searched for matching packages. * * @param name fully qualified package name, or an empty string for an unnamed package * @return the specified package, or {@code null} if it cannot be uniquely found */ PackageElement getPackageElement(CharSequence name); /** * Returns a package given its fully qualified name, as seen from the given module. * * @implSpec The default implementation of this method returns * {@code null}. * * @param name fully qualified package name, or an empty string for an unnamed package * @param module module relative to which the lookup should happen * @return the specified package, or {@code null} if it cannot be found * @see #getAllPackageElements * @since 9 */ default PackageElement getPackageElement(ModuleElement module, CharSequence name) { return null; } /** * Returns all package elements with the given canonical name. * * There may be more than one package element with the same canonical * name if the package elements are in different modules. * * @implSpec The default implementation of this method calls * {@link #getAllModuleElements() getAllModuleElements} and stores * the result. If the set of modules is empty, {@link * #getPackageElement(CharSequence) getPackageElement(name)} is * called passing through the name argument. If {@code * getPackageElement(name)} is {@code null}, an empty set of * package elements is returned; otherwise, a single-element set * with the found package element is returned. If the set of * modules is nonempty, the modules are iterated over and any * non-{@code null} results of {@link * #getPackageElement(ModuleElement, CharSequence) * getPackageElement(module, name)} are accumulated into a * set. The set is then returned. * * @param name the canonical name * @return the package elements, or an empty set if no package with the name can be found * @see #getPackageElement(ModuleElement, CharSequence) * @since 9 */ default Set<? extends PackageElement> getAllPackageElements(CharSequence name) { Set<? extends ModuleElement> modules = getAllModuleElements(); if (modules.isEmpty()) { PackageElement packageElt = getPackageElement(name); return (packageElt != null) ? Collections.singleton(packageElt) : Collections.emptySet(); } else { Set<PackageElement> result = new LinkedHashSet<>(1); // Usually expect at most 1 result for (ModuleElement module : modules) { PackageElement packageElt = getPackageElement(module, name); if (packageElt != null) result.add(packageElt); } return Collections.unmodifiableSet(result); } } /** * Returns a type element given its canonical name if the type element is unique in the environment. * If running with modules, all modules in the modules graph are searched for matching * type elements. * * @param name the canonical name * @return the named type element, or {@code null} if it cannot be uniquely found */ TypeElement getTypeElement(CharSequence name); /** * Returns a type element given its canonical name, as seen from the given module. * * @implSpec The default implementation of this method returns * {@code null}. * * @param name the canonical name * @param module module relative to which the lookup should happen * @return the named type element, or {@code null} if it cannot be found * @see #getAllTypeElements * @since 9 */ default TypeElement getTypeElement(ModuleElement module, CharSequence name) { return null; } /** * Returns all type elements with the given canonical name. * * There may be more than one type element with the same canonical * name if the type elements are in different modules. * * @implSpec The default implementation of this method calls * {@link #getAllModuleElements() getAllModuleElements} and stores * the result. If the set of modules is empty, {@link * #getTypeElement(CharSequence) getTypeElement(name)} is called * passing through the name argument. If {@code * getTypeElement(name)} is {@code null}, an empty set of type * elements is returned; otherwise, a single-element set with the * found type element is returned. If the set of modules is * nonempty, the modules are iterated over and any non-{@code null} * results of {@link #getTypeElement(ModuleElement, * CharSequence) getTypeElement(module, name)} are accumulated * into a set. The set is then returned. * * @param name the canonical name * @return the type elements, or an empty set if no type with the name can be found * @see #getTypeElement(ModuleElement, CharSequence) * @since 9 */ default Set<? extends TypeElement> getAllTypeElements(CharSequence name) { Set<? extends ModuleElement> modules = getAllModuleElements(); if (modules.isEmpty()) { TypeElement typeElt = getTypeElement(name); return (typeElt != null) ? Collections.singleton(typeElt) : Collections.emptySet(); } else { Set<TypeElement> result = new LinkedHashSet<>(1); // Usually expect at most 1 result for (ModuleElement module : modules) { TypeElement typeElt = getTypeElement(module, name); if (typeElt != null) result.add(typeElt); } return Collections.unmodifiableSet(result); } } /** * Returns a module element given its fully qualified name. * * If the requested module cannot be found, {@code null} is * returned. One situation where a module cannot be found is if * the environment does not include modules, such as an annotation * processing environment configured for a {@linkplain * javax.annotation.processing.ProcessingEnvironment#getSourceVersion * source version} without modules. * * @implSpec The default implementation of this method returns * {@code null}. * * @param name the name, or an empty string for an unnamed module * @return the named module element, or {@code null} if it cannot be found * @see #getAllModuleElements * @since 9 * @spec JPMS */ default ModuleElement getModuleElement(CharSequence name) { return null; } /** * Returns all module elements in the current environment. * * If no modules are present, an empty set is returned. One * situation where no modules are present occurs when the * environment does not include modules, such as an annotation * processing environment configured for a {@linkplain * javax.annotation.processing.ProcessingEnvironment#getSourceVersion * source version} without modules. * * @implSpec The default implementation of this method returns * an empty set. * * @return the known module elements, or an empty set if there are no modules * @see #getModuleElement(CharSequence) * @since 9 */ default Set<? extends ModuleElement> getAllModuleElements() { return Collections.emptySet(); } /** * Returns the values of an annotation's elements, including defaults. * * @see AnnotationMirror#getElementValues() * @param a annotation to examine * @return the values of the annotation's elements, including defaults */ Map<? extends ExecutableElement, ? extends AnnotationValue> getElementValuesWithDefaults(AnnotationMirror a); /** * Returns the text of the documentation ("Javadoc") * comment of an element. * * <p> A documentation comment of an element is a comment that * begins with "{@code /**}" , ends with a separate * "<code>*/</code>", and immediately precedes the element, * ignoring white space. Therefore, a documentation comment * contains at least three"{@code *}" characters. The text * returned for the documentation comment is a processed form of * the comment as it appears in source code. The leading "{@code * /**}" and trailing "<code>*/</code>" are removed. For lines * of the comment starting after the initial "{@code /**}", * leading white space characters are discarded as are any * consecutive "{@code *}" characters appearing after the white * space or starting the line. The processed lines are then * concatenated together (including line terminators) and * returned. * * @param e the element being examined * @return the documentation comment of the element, or {@code null} * if there is none * @jls 3.6 White Space */ String getDocComment(Element e); /** * Returns {@code true} if the element is deprecated, {@code false} otherwise. * * @param e the element being examined * @return {@code true} if the element is deprecated, {@code false} otherwise */ boolean isDeprecated(Element e); /** * Returns the <em>origin</em> of the given element. * * <p>Note that if this method returns {@link Origin#EXPLICIT * EXPLICIT} and the element was created from a class file, then * the element may not, in fact, correspond to an explicitly * declared construct in source code. This is due to limitations * of the fidelity of the class file format in preserving * information from source code. For example, at least some * versions of the class file format do not preserve whether a * constructor was explicitly declared by the programmer or was * implicitly declared as the <em>default constructor</em>. * * @implSpec The default implementation of this method returns * {@link Origin#EXPLICIT EXPLICIT}. * * @param e the element being examined * @return the origin of the given element * @since 9 */ default Origin getOrigin(Element e) { return Origin.EXPLICIT; } /** * Returns the <em>origin</em> of the given annotation mirror. * * An annotation mirror is {@linkplain Origin#MANDATED mandated} * if it is an implicitly declared <em>container annotation</em> * used to hold repeated annotations of a repeatable annotation * type. * * <p>Note that if this method returns {@link Origin#EXPLICIT * EXPLICIT} and the annotation mirror was created from a class * file, then the element may not, in fact, correspond to an * explicitly declared construct in source code. This is due to * limitations of the fidelity of the class file format in * preserving information from source code. For example, at least * some versions of the class file format do not preserve whether * an annotation was explicitly declared by the programmer or was * implicitly declared as a <em>container annotation</em>. * * @implSpec The default implementation of this method returns * {@link Origin#EXPLICIT EXPLICIT}. * * @param c the construct the annotation mirror modifies * @param a the annotation mirror being examined * @return the origin of the given annotation mirror * @jls 9.6.3 Repeatable Annotation Types * @jls 9.7.5 Multiple Annotations of the Same Type * @since 9 */ default Origin getOrigin(AnnotatedConstruct c, AnnotationMirror a) { return Origin.EXPLICIT; } /** * Returns the <em>origin</em> of the given module directive. * * <p>Note that if this method returns {@link Origin#EXPLICIT * EXPLICIT} and the module directive was created from a class * file, then the module directive may not, in fact, correspond to * an explicitly declared construct in source code. This is due to * limitations of the fidelity of the class file format in * preserving information from source code. For example, at least * some versions of the class file format do not preserve whether * a {@code uses} directive was explicitly declared by the * programmer or was added as a synthetic construct. * * <p>Note that an implementation may not be able to reliably * determine the origin status of the directive if the directive * is created from a class file due to limitations of the fidelity * of the class file format in preserving information from source * code. * * @implSpec The default implementation of this method returns * {@link Origin#EXPLICIT EXPLICIT}. * * @param m the module of the directive * @param directive the module directive being examined * @return the origin of the given directive * @since 9 */ default Origin getOrigin(ModuleElement m, ModuleElement.Directive directive) { return Origin.EXPLICIT; } /** * The <em>origin</em> of an element or other language model * item. The origin of an element or item models how a construct * in a program is declared in the source code, explicitly, * implicitly, etc. * * <p>Note that it is possible additional kinds of origin values * will be added in future versions of the platform. * * @jls 13.1 The Form of a Binary * @since 9 */ public enum Origin { /** * Describes a construct explicitly declared in source code. */ EXPLICIT, /** * A mandated construct is one that is not explicitly declared * in the source code, but whose presence is mandated by the * specification. Such a construct is said to be implicitly * declared. * * One example of a mandated element is a <em>default * constructor</em> in a class that contains no explicit * constructor declarations. * * Another example of a mandated construct is an implicitly * declared <em>container annotation</em> used to hold * multiple annotations of a repeatable annotation type. * * @jls 8.8.9 Default Constructor * @jls 8.9.3 Enum Members * @jls 9.6.3 Repeatable Annotation Types * @jls 9.7.5 Multiple Annotations of the Same Type */ MANDATED, /** * A synthetic construct is one that is neither implicitly nor * explicitly declared in the source code. Such a construct is * typically a translation artifact created by a compiler. */ SYNTHETIC; /** * Returns {@code true} for values corresponding to constructs * that are implicitly or explicitly declared, {@code false} * otherwise. * @return {@code true} for {@link EXPLICIT} and {@link * MANDATED}, {@code false} otherwise. */ public boolean isDeclared() { return this != SYNTHETIC; } } /** * Returns {@code true} if the executable element is a bridge * method, {@code false} otherwise. * * @implSpec The default implementation of this method returns {@code false}. * * @param e the executable being examined * @return {@code true} if the executable element is a bridge * method, {@code false} otherwise * @since 9 */ default boolean isBridge(ExecutableElement e) { return false; } /** * Returns the <i>binary name</i> of a type element. * * @param type the type element being examined * @return the binary name * * @see TypeElement#getQualifiedName * @jls 13.1 The Form of a Binary */ Name getBinaryName(TypeElement type); /** * Returns the package of an element. The package of a package is * itself. * The package of a module is {@code null}. * * @param type the element being examined * @return the package of an element */ PackageElement getPackageOf(Element type); /** * Returns the module of an element. The module of a module is * itself. * If there is no module for the element, null is returned. One situation where there is * no module for an element is if the environment does not include modules, such as * an annotation processing environment configured for * a {@linkplain * javax.annotation.processing.ProcessingEnvironment#getSourceVersion * source version} without modules. * * @implSpec The default implementation of this method returns * {@code null}. * * @param type the element being examined * @return the module of an element * @since 9 * @spec JPMS */ default ModuleElement getModuleOf(Element type) { return null; } /** * Returns all members of a type element, whether inherited or * declared directly. For a class the result also includes its * constructors, but not local or anonymous classes. * * @apiNote Elements of certain kinds can be isolated using * methods in {@link ElementFilter}. * * @param type the type being examined * @return all members of the type * @see Element#getEnclosedElements */ List<? extends Element> getAllMembers(TypeElement type); /** * Returns all annotations <i>present</i> on an element, whether * directly present or present via inheritance. * * @param e the element being examined * @return all annotations of the element * @see Element#getAnnotationMirrors * @see javax.lang.model.AnnotatedConstruct */ List<? extends AnnotationMirror> getAllAnnotationMirrors(Element e); /** * Tests whether one type, method, or field hides another. * * @param hider the first element * @param hidden the second element * @return {@code true} if and only if the first element hides * the second * @jls 8.4.8 Inheritance, Overriding, and Hiding */ boolean hides(Element hider, Element hidden); /** * Tests whether one method, as a member of a given type, * overrides another method. * When a non-abstract method overrides an abstract one, the * former is also said to <i>implement</i> the latter. * * <p> In the simplest and most typical usage, the value of the * {@code type} parameter will simply be the class or interface * directly enclosing {@code overrider} (the possibly-overriding * method). For example, suppose {@code m1} represents the method * {@code String.hashCode} and {@code m2} represents {@code * Object.hashCode}. We can then ask whether {@code m1} overrides * {@code m2} within the class {@code String} (it does): * * <blockquote> * {@code assert elements.overrides(m1, m2, * elements.getTypeElement("java.lang.String")); } * </blockquote> * * A more interesting case can be illustrated by the following example * in which a method in type {@code A} does not override a * like-named method in type {@code B}: * * <blockquote> * {@code class A { public void m() {} } }<br> * {@code interface B { void m(); } }<br> * ...<br> * {@code m1 = ...; // A.m }<br> * {@code m2 = ...; // B.m }<br> * {@code assert ! elements.overrides(m1, m2, * elements.getTypeElement("A")); } * </blockquote> * * When viewed as a member of a third type {@code C}, however, * the method in {@code A} does override the one in {@code B}: * * <blockquote> * {@code class C extends A implements B {} }<br> * ...<br> * {@code assert elements.overrides(m1, m2, * elements.getTypeElement("C")); } * </blockquote> * * @param overrider the first method, possible overrider * @param overridden the second method, possibly being overridden * @param type the type of which the first method is a member * @return {@code true} if and only if the first method overrides * the second * @jls 8.4.8 Inheritance, Overriding, and Hiding * @jls 9.4.1 Inheritance and Overriding */ boolean overrides(ExecutableElement overrider, ExecutableElement overridden, TypeElement type); /** * Returns the text of a <i>constant expression</i> representing a * primitive value or a string. * The text returned is in a form suitable for representing the value * in source code. * * @param value a primitive value or string * @return the text of a constant expression * @throws IllegalArgumentException if the argument is not a primitive * value or string * * @see VariableElement#getConstantValue() */ String getConstantExpression(Object value); /** * Prints a representation of the elements to the given writer in * the specified order. The main purpose of this method is for * diagnostics. The exact format of the output is <em>not</em> * specified and is subject to change. * * @param w the writer to print the output to * @param elements the elements to print */ void printElements(java.io.Writer w, Element... elements); /** * Return a name with the same sequence of characters as the * argument. * * @param cs the character sequence to return as a name * @return a name with the same sequence of characters as the argument */ Name getName(CharSequence cs); /** * Returns {@code true} if the type element is a functional interface, {@code false} otherwise. * * @param type the type element being examined * @return {@code true} if the element is a functional interface, {@code false} otherwise * @jls 9.8 Functional Interfaces * @since 1.8 */ boolean isFunctionalInterface(TypeElement type); }