android-34/dalvik/annotation/MethodParameters.java

/*
 * Copyright (C) 2016 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package dalvik.annotation;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.lang.reflect.Parameter;

/**
 * A system annotation that can optionally be used to provide parameter metadata such as
 * parameter names and modifiers.
 *
 * <p>The annotation can be omitted from a method / constructor safely when the parameter metadata
 * is not needed / desired at runtime. {@link Parameter#isNamePresent()} can be used to check
 * whether metadata is present for a parameter, and the associated reflection methods like
 * {@link java.lang.reflect.Parameter#getName()} will fall back to default behavior at runtime if
 * the information is not present.
 *
 * <p>When including parameter metadata, compilers should include parameter metadata for generated
 * classes like enums, since the parameter metadata includes whether or not a parameter is
 * synthetic or mandated.
 *
 * <p>MethodParameters currently only describes individual method parameters and there is no
 * mechanism to detect whether parameter method data is <em>generally</em> present for an
 * {@link java.lang.reflect.Executable}. Therefore, it is code-size and runtime efficient to omit
 * the annotation entirely for constructors and methods that have no parameters.
 */
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.CONSTRUCTOR, ElementType.METHOD})
@interface MethodParameters {

    /*
     * This annotation is never used in source code; it is expected to be generated in .dex
     * files by tools like compilers. Commented definitions for the annotation members expected
     * by the runtime / reflection code can be found below for reference.
     *
     * The arrays documented below must be the same size as for the method_id_item dex structure
     * associated with the method otherwise a java.lang.reflect.MalformedParametersException will
     * be thrown at runtime.
     *
     * That is: method_id_item.proto_idx -> proto_id_item.parameters_off -> type_list.size must
     * be the same as names().length and accessFlags().length.
     *
     * Because MethodParameters describes all formal method parameters, even those not explicitly
     * or implicitly declared in source code, the size of the arrays may differ from the Signature
     * or other metadata information that can be based only on explicit parameters declared in
     * source code. MethodParameters will also not include any information about type annotation
     * receiver parameters that do not exist in the actual method signature.
     */


    /*
     * The names of formal parameters for the associated method. The array cannot be null, but can
     * be empty if there are no formal parameters. A value in the array can be null if the formal
     * parameter with that index has no name.
     *
     * If parameter name Strings are empty or contain '.', ';', '[' or '/' then a
     * java.lang.reflect.MalformedParametersException will be thrown at runtime.
     */
    // String[] names();

    /*
     * The access flags of the formal parameters for the associated method. The array cannot be
     * null, but can be empty if there are no formal parameters.
     *
     * The value is a bit mask with the follow values:
     * 0x0010 : final, the parameter was declared final
     * 0x1000 : synthetic, the parameter was introduced by the compiler.
     * 0x8000 : mandated, the parameter is synthetic but also implied by the language
     *          specification.
     *
     * If any bits are set outside of this set then a java.lang.reflect.MalformedParametersException
     * will be thrown at runtime.
     */
    // int[] accessFlags();
}