Java tutorial
/* * Copyright (c) 2013, 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 java.lang.reflect; import java.lang.annotation.*; import java.util.HashMap; import java.util.Map; import java.util.Objects; import sun.reflect.annotation.AnnotationSupport; /** * Information about method parameters. * * A {@code Parameter} provides information about method parameters, * including its name and modifiers. It also provides an alternate * means of obtaining attributes for the parameter. * * @since 1.8 */ public final class Parameter implements AnnotatedElement { private final String name; private final int modifiers; private final Executable executable; private final int index; /** * Package-private constructor for {@code Parameter}. * * If method parameter data is present in the classfile, then the * JVM creates {@code Parameter} objects directly. If it is * absent, however, then {@code Executable} uses this constructor * to synthesize them. * * @param name The name of the parameter. * @param modifiers The modifier flags for the parameter. * @param executable The executable which defines this parameter. * @param index The index of the parameter. */ Parameter(String name, int modifiers, Executable executable, int index) { this.name = name; this.modifiers = modifiers; this.executable = executable; this.index = index; } /** * Compares based on the executable and the index. * * @param obj The object to compare. * @return Whether or not this is equal to the argument. */ public boolean equals(Object obj) { if (obj instanceof Parameter) { Parameter other = (Parameter) obj; return (other.executable.equals(executable) && other.index == index); } return false; } /** * Returns a hash code based on the executable's hash code and the * index. * * @return A hash code based on the executable's hash code. */ public int hashCode() { return executable.hashCode() ^ index; } /** * Returns true if the parameter has a name according to the class * file; returns false otherwise. Whether a parameter has a name * is determined by the {@literal MethodParameters} attribute of * the method which declares the parameter. * * @return true if and only if the parameter has a name according * to the class file. */ public boolean isNamePresent() { return executable.hasRealParameterData() && name != null; } /** * Returns a string describing this parameter. The format is the * modifiers for the parameter, if any, in canonical order as * recommended by <cite>The Java™ Language * Specification</cite>, followed by the fully- qualified type of * the parameter (excluding the last [] if the parameter is * variable arity), followed by "..." if the parameter is variable * arity, followed by a space, followed by the name of the * parameter. * * @return A string representation of the parameter and associated * information. */ public String toString() { final StringBuilder sb = new StringBuilder(); final Type type = getParameterizedType(); final String typename = type.getTypeName(); sb.append(Modifier.toString(getModifiers())); if (0 != modifiers) sb.append(' '); if (isVarArgs()) sb.append(typename.replaceFirst("\\[\\]$", "...")); else sb.append(typename); sb.append(' '); sb.append(getName()); return sb.toString(); } /** * Return the {@code Executable} which declares this parameter. * * @return The {@code Executable} declaring this parameter. */ public Executable getDeclaringExecutable() { return executable; } /** * Get the modifier flags for this the parameter represented by * this {@code Parameter} object. * * @return The modifier flags for this parameter. */ public int getModifiers() { return modifiers; } /** * Returns the name of the parameter. If the parameter's name is * {@linkplain #isNamePresent() present}, then this method returns * the name provided by the class file. Otherwise, this method * synthesizes a name of the form argN, where N is the index of * the parameter in the descriptor of the method which declares * the parameter. * * @return The name of the parameter, either provided by the class * file or synthesized if the class file does not provide * a name. */ public String getName() { // Note: empty strings as parameter names are now outlawed. // The .isEmpty() is for compatibility with current JVM // behavior. It may be removed at some point. if (name == null || name.isEmpty()) return "arg" + index; else return name; } // Package-private accessor to the real name field. String getRealName() { return name; } /** * Returns a {@code Type} object that identifies the parameterized * type for the parameter represented by this {@code Parameter} * object. * * @return a {@code Type} object identifying the parameterized * type of the parameter represented by this object */ public Type getParameterizedType() { Type tmp = parameterTypeCache; if (null == tmp) { tmp = executable.getAllGenericParameterTypes()[index]; parameterTypeCache = tmp; } return tmp; } private transient volatile Type parameterTypeCache; /** * Returns a {@code Class} object that identifies the * declared type for the parameter represented by this * {@code Parameter} object. * * @return a {@code Class} object identifying the declared * type of the parameter represented by this object */ public Class<?> getType() { Class<?> tmp = parameterClassCache; if (null == tmp) { tmp = executable.getParameterTypes()[index]; parameterClassCache = tmp; } return tmp; } /** * Returns an AnnotatedType object that represents the use of a type to * specify the type of the formal parameter represented by this Parameter. * * @return an {@code AnnotatedType} object representing the use of a type * to specify the type of the formal parameter represented by this * Parameter */ public AnnotatedType getAnnotatedType() { // no caching for now return executable.getAnnotatedParameterTypes()[index]; } private transient volatile Class<?> parameterClassCache; /** * Returns {@code true} if this parameter is implicitly declared * in source code; returns {@code false} otherwise. * * @return true if and only if this parameter is implicitly * declared as defined by <cite>The Java™ Language * Specification</cite>. */ public boolean isImplicit() { return Modifier.isMandated(getModifiers()); } /** * Returns {@code true} if this parameter is neither implicitly * nor explicitly declared in source code; returns {@code false} * otherwise. * * @jls 13.1 The Form of a Binary * @return true if and only if this parameter is a synthetic * construct as defined by * <cite>The Java™ Language Specification</cite>. */ public boolean isSynthetic() { return Modifier.isSynthetic(getModifiers()); } /** * Returns {@code true} if this parameter represents a variable * argument list; returns {@code false} otherwise. * * @return {@code true} if an only if this parameter represents a * variable argument list. */ public boolean isVarArgs() { return executable.isVarArgs() && index == executable.getParameterCount() - 1; } /** * {@inheritDoc} * @throws NullPointerException {@inheritDoc} */ public <T extends Annotation> T getAnnotation(Class<T> annotationClass) { Objects.requireNonNull(annotationClass); return annotationClass.cast(declaredAnnotations().get(annotationClass)); } /** * {@inheritDoc} * @throws NullPointerException {@inheritDoc} */ @Override public <T extends Annotation> T[] getAnnotationsByType(Class<T> annotationClass) { Objects.requireNonNull(annotationClass); return AnnotationSupport.getDirectlyAndIndirectlyPresent(declaredAnnotations(), annotationClass); } /** * {@inheritDoc} */ public Annotation[] getDeclaredAnnotations() { return executable.getParameterAnnotations()[index]; } /** * @throws NullPointerException {@inheritDoc} */ public <T extends Annotation> T getDeclaredAnnotation(Class<T> annotationClass) { // Only annotations on classes are inherited, for all other // objects getDeclaredAnnotation is the same as // getAnnotation. return getAnnotation(annotationClass); } /** * @throws NullPointerException {@inheritDoc} */ @Override public <T extends Annotation> T[] getDeclaredAnnotationsByType(Class<T> annotationClass) { // Only annotations on classes are inherited, for all other // objects getDeclaredAnnotations is the same as // getAnnotations. return getAnnotationsByType(annotationClass); } /** * {@inheritDoc} */ public Annotation[] getAnnotations() { return getDeclaredAnnotations(); } private transient Map<Class<? extends Annotation>, Annotation> declaredAnnotations; private synchronized Map<Class<? extends Annotation>, Annotation> declaredAnnotations() { if (null == declaredAnnotations) { declaredAnnotations = new HashMap<>(); for (Annotation a : getDeclaredAnnotations()) declaredAnnotations.put(a.annotationType(), a); } return declaredAnnotations; } }