ElementFilter.java

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * This code is free software; you can redistribute it and/or modify it
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 * particular file as subject to the "Classpath" exception as provided
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 * 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).
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 * 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.
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package javax.lang.model.util;

import java.util.Collections;
import java.util.List;
import java.util.Set;
import java.util.EnumSet;
import java.util.ArrayList;
import java.util.LinkedHashSet;

import javax.lang.model.element.*;
import javax.lang.model.element.ModuleElement.Directive;
import javax.lang.model.element.ModuleElement.DirectiveKind;
import javax.lang.model.element.ModuleElement.ExportsDirective;
import javax.lang.model.element.ModuleElement.OpensDirective;
import javax.lang.model.element.ModuleElement.ProvidesDirective;
import javax.lang.model.element.ModuleElement.RequiresDirective;
import javax.lang.model.element.ModuleElement.UsesDirective;

/**
 * Filters for selecting just the elements of interest from a
 * collection of elements.  The returned sets and lists are new
 * collections and do use the argument as a backing store.  The
 * methods in this class do not make any attempts to guard against
 * concurrent modifications of the arguments.  The returned sets and
 * lists are mutable but unsafe for concurrent access.  A returned set
 * has the same iteration order as the argument set to a method.
 *
 * <p>If iterables and sets containing {@code null} are passed as
 * arguments to methods in this class, a {@code NullPointerException}
 * will be thrown.
 *
 * @author Joseph D. Darcy
 * @author Scott Seligman
 * @author Peter von der Ah&eacute;
 * @author Martin Buchholz
 * @since 1.6
 */
// 元素/指令过滤器
public class ElementFilter {
    
    private static final Set<ElementKind> CONSTRUCTOR_KIND
        = Collections.unmodifiableSet(EnumSet.of(ElementKind.CONSTRUCTOR));
    
    private static final Set<ElementKind> FIELD_KINDS
        = Collections.unmodifiableSet(EnumSet.of(ElementKind.FIELD, ElementKind.ENUM_CONSTANT));
    
    private static final Set<ElementKind> METHOD_KIND
        = Collections.unmodifiableSet(EnumSet.of(ElementKind.METHOD));
    
    private static final Set<ElementKind> PACKAGE_KIND
        = Collections.unmodifiableSet(EnumSet.of(ElementKind.PACKAGE));
    
    private static final Set<ElementKind> MODULE_KIND
        = Collections.unmodifiableSet(EnumSet.of(ElementKind.MODULE));
    
    private static final Set<ElementKind> TYPE_KINDS
        = Collections.unmodifiableSet(EnumSet.of(ElementKind.CLASS, ElementKind.ENUM, ElementKind.INTERFACE, ElementKind.ANNOTATION_TYPE));
    
    
    
    private ElementFilter() {
    } // Do not instantiate.
    
    
    
    /**
     * Returns a list of fields in {@code elements}.
     *
     * @param elements the elements to filter
     *
     * @return a list of fields in {@code elements}
     */
    // 从elements中筛选出符合FIELD_KINDS类型的元素
    public static List<VariableElement> fieldsIn(Iterable<? extends Element> elements) {
        return listFilter(elements, FIELD_KINDS, VariableElement.class);
    }
    
    /**
     * Returns a list of constructors in {@code elements}.
     *
     * @param elements the elements to filter
     *
     * @return a list of constructors in {@code elements}
     */
    // 从elements中筛选出符合CONSTRUCTOR_KIND类型的元素
    public static List<ExecutableElement> constructorsIn(Iterable<? extends Element> elements) {
        return listFilter(elements, CONSTRUCTOR_KIND, ExecutableElement.class);
    }
    
    /**
     * Returns a list of methods in {@code elements}.
     *
     * @param elements the elements to filter
     *
     * @return a list of methods in {@code elements}
     */
    // 从elements中筛选出符合METHOD_KIND类型的元素
    public static List<ExecutableElement> methodsIn(Iterable<? extends Element> elements) {
        return listFilter(elements, METHOD_KIND, ExecutableElement.class);
    }
    
    /**
     * Returns a list of types in {@code elements}.
     *
     * @param elements the elements to filter
     *
     * @return a list of types in {@code elements}
     */
    // 从elements中筛选出符合TYPE_KINDS类型的元素
    public static List<TypeElement> typesIn(Iterable<? extends Element> elements) {
        return listFilter(elements, TYPE_KINDS, TypeElement.class);
    }
    
    /**
     * Returns a list of packages in {@code elements}.
     *
     * @param elements the elements to filter
     *
     * @return a list of packages in {@code elements}
     */
    // 从elements中筛选出符合PACKAGE_KIND类型的元素
    public static List<PackageElement> packagesIn(Iterable<? extends Element> elements) {
        return listFilter(elements, PACKAGE_KIND, PackageElement.class);
    }
    
    /**
     * Returns a list of modules in {@code elements}.
     *
     * @param elements the elements to filter
     *
     * @return a list of modules in {@code elements}
     *
     * @spec JPMS
     * @since 9
     */
    // 从elements中筛选出符合MODULE_KIND类型的元素
    public static List<ModuleElement> modulesIn(Iterable<? extends Element> elements) {
        return listFilter(elements, MODULE_KIND, ModuleElement.class);
    }
    
    
    
    /**
     * Returns a set of fields in {@code elements}.
     *
     * @param elements the elements to filter
     *
     * @return a set of fields in {@code elements}
     */
    // 从elements中筛选出符合FIELD_KINDS类型的元素
    public static Set<VariableElement> fieldsIn(Set<? extends Element> elements) {
        return setFilter(elements, FIELD_KINDS, VariableElement.class);
    }
    
    /**
     * Returns a set of constructors in {@code elements}.
     *
     * @param elements the elements to filter
     *
     * @return a set of constructors in {@code elements}
     */
    // 从elements中筛选出符合CONSTRUCTOR_KIND类型的元素
    public static Set<ExecutableElement> constructorsIn(Set<? extends Element> elements) {
        return setFilter(elements, CONSTRUCTOR_KIND, ExecutableElement.class);
    }
    
    /**
     * Returns a set of methods in {@code elements}.
     *
     * @param elements the elements to filter
     *
     * @return a set of methods in {@code elements}
     */
    // 从elements中筛选出符合METHOD_KIND类型的元素
    public static Set<ExecutableElement> methodsIn(Set<? extends Element> elements) {
        return setFilter(elements, METHOD_KIND, ExecutableElement.class);
    }
    
    /**
     * Returns a set of types in {@code elements}.
     *
     * @param elements the elements to filter
     *
     * @return a set of types in {@code elements}
     */
    // 从elements中筛选出符合TYPE_KINDS类型的元素
    public static Set<TypeElement> typesIn(Set<? extends Element> elements) {
        return setFilter(elements, TYPE_KINDS, TypeElement.class);
    }
    
    /**
     * Returns a set of packages in {@code elements}.
     *
     * @param elements the elements to filter
     *
     * @return a set of packages in {@code elements}
     */
    // 从elements中筛选出符合PACKAGE_KIND类型的元素
    public static Set<PackageElement> packagesIn(Set<? extends Element> elements) {
        return setFilter(elements, PACKAGE_KIND, PackageElement.class);
    }
    
    /**
     * Returns a set of modules in {@code elements}.
     *
     * @param elements the elements to filter
     *
     * @return a set of modules in {@code elements}
     *
     * @spec JPMS
     * @since 9
     */
    // 从elements中筛选出符合MODULE_KIND类型的元素
    public static Set<ModuleElement> modulesIn(Set<? extends Element> elements) {
        return setFilter(elements, MODULE_KIND, ModuleElement.class);
    }
    
    
    
    /**
     * Returns a list of {@code exports} directives in {@code directives}.
     *
     * @param directives the directives to filter
     *
     * @return a list of {@code exports} directives in {@code directives}
     *
     * @spec JPMS
     * @since 9
     */
    // 从directives中筛选出exports类型的指令
    public static List<ExportsDirective> exportsIn(Iterable<? extends Directive> directives) {
        return listFilter(directives, DirectiveKind.EXPORTS, ExportsDirective.class);
    }
    
    /**
     * Returns a list of {@code opens} directives in {@code directives}.
     *
     * @param directives the directives to filter
     *
     * @return a list of {@code opens} directives in {@code directives}
     *
     * @since 9
     */
    // 从directives中筛选出opens类型的指令
    public static List<OpensDirective> opensIn(Iterable<? extends Directive> directives) {
        return listFilter(directives, DirectiveKind.OPENS, OpensDirective.class);
    }
    
    /**
     * Returns a list of {@code provides} directives in {@code directives}.
     *
     * @param directives the directives to filter
     *
     * @return a list of {@code provides} directives in {@code directives}
     *
     * @spec JPMS
     * @since 9
     */
    // 从directives中筛选出provides类型的指令
    public static List<ProvidesDirective> providesIn(Iterable<? extends Directive> directives) {
        return listFilter(directives, DirectiveKind.PROVIDES, ProvidesDirective.class);
    }
    
    /**
     * Returns a list of {@code requires} directives in {@code directives}.
     *
     * @param directives the directives to filter
     *
     * @return a list of {@code requires} directives in {@code directives}
     *
     * @spec JPMS
     * @since 9
     */
    // 从directives中筛选出requires类型的指令
    public static List<RequiresDirective> requiresIn(Iterable<? extends Directive> directives) {
        return listFilter(directives, DirectiveKind.REQUIRES, RequiresDirective.class);
    }
    
    /**
     * Returns a list of {@code uses} directives in {@code directives}.
     *
     * @param directives the directives to filter
     *
     * @return a list of {@code uses} directives in {@code directives}
     *
     * @spec JPMS
     * @since 9
     */
    // 从directives中筛选出uses类型的指令
    public static List<UsesDirective> usesIn(Iterable<? extends Directive> directives) {
        return listFilter(directives, DirectiveKind.USES, UsesDirective.class);
    }
    
    
    
    // 从elements中筛选出符合targetKinds类型的元素
    private static <E extends Element> List<E> listFilter(Iterable<? extends Element> elements, Set<ElementKind> targetKinds, Class<E> clazz) {
        List<E> list = new ArrayList<>();
        for(Element e : elements) {
            if(targetKinds.contains(e.getKind())) {
                list.add(clazz.cast(e));
            }
        }
        return list;
    }
    
    // 从elements中筛选出符合targetKinds类型的元素
    private static <E extends Element> Set<E> setFilter(Set<? extends Element> elements, Set<ElementKind> targetKinds, Class<E> clazz) {
        // Return set preserving iteration order of input set.
        Set<E> set = new LinkedHashSet<>();
        for(Element e : elements) {
            if(targetKinds.contains(e.getKind())) {
                set.add(clazz.cast(e));
            }
        }
        return set;
    }
    
    // 从directives中筛选出符合directiveKind类型的指令
    private static <D extends Directive> List<D> listFilter(Iterable<? extends Directive> directives, DirectiveKind directiveKind, Class<D> clazz) {
        List<D> list = new ArrayList<>();
        for(Directive d : directives) {
            if(d.getKind() == directiveKind) {
                list.add(clazz.cast(d));
            }
        }
        return list;
    }
}