1 /* 2 * Copyright (C) 2018 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package dalvik.annotation.codegen; 18 19 import java.lang.annotation.ElementType; 20 import java.lang.annotation.Repeatable; 21 import java.lang.annotation.Retention; 22 import java.lang.annotation.RetentionPolicy; 23 import java.lang.annotation.Target; 24 25 /** 26 * Indicates to the platform toolchain that there is an upcoming public SDK API change for a method. 27 * The API change will add a more specific return type in a subclass for an overridden method. 28 * 29 * <p>When this annotation is present, the toolchain is required to generate on-device bytecode for 30 * an overloaded implementation of the method which is marked as synthetic, returns the more 31 * specific type given in {@link CovariantReturnType#returnType()}, and which delegates to the 32 * method being annotated. 33 * 34 * <p>At some future point in time the public Android API can change so that the public API method 35 * returns the new type. Android platform developers can be sure that all releases after the API 36 * version specified in {@link CovariantReturnType#presentAfter()} have the new method signature on 37 * device and will therefore be compatible with code compiled against the newest public Android API 38 * stubs. 39 * 40 * <p>Once the actual method signature is updated to the new form and this annotation is removed 41 * there will be a synthetic overload for the method with the more general type provided (as normal) 42 * by the Java compiler ensuring compatibility with code compiled against the old stubs. 43 * 44 * <p>When adding this annotation to platform classes the developer should also add CTS tests to 45 * ensure the expected methods are present on all Android devices. 46 * 47 * <p>Notes on scope and limitations: 48 * <ul> 49 * <li>This annotation must have no effect on generated API stubs.</li> 50 * <li>This annotation does not allow the declared exceptions to be made more specific for the 51 * generated synthetic method. This could be added later.</li> 52 * <li>Any type parameters on the annotated method need not be copied.</li> 53 * <li>This annotation is <em>not</em> expected to be treated by the toolchain as inherited. All 54 * layers of platform class hierarchy must specify {@link CovariantReturnType} for all the overloads 55 * that have to be generated. The annotation is marked as repeatable for this reason.</li> 56 * </ul> 57 * 58 * @hide 59 */ 60 @Repeatable(CovariantReturnType.CovariantReturnTypes.class) 61 @Retention(RetentionPolicy.CLASS) 62 @Target({ ElementType.METHOD}) 63 public @interface CovariantReturnType { 64 65 /** 66 * The return type of the synthetic method to generate. Must be a subclass of the return type 67 * of the method being annotated. 68 */ returnType()69 Class<?> returnType(); 70 71 /** 72 * The last Android API level not to have the generated synthetic method. The annotation can be 73 * removed and the actual return type updated when support for this API level is dropped. 74 */ presentAfter()75 int presentAfter(); 76 77 /** @hide */ 78 @Retention(RetentionPolicy.CLASS) 79 @Target({ElementType.METHOD}) 80 @interface CovariantReturnTypes { value()81 CovariantReturnType[] value(); 82 } 83 } 84