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 static android.annotation.SystemApi.Client.MODULE_LIBRARIES; 20 21 import android.annotation.SystemApi; 22 23 import java.lang.annotation.ElementType; 24 import java.lang.annotation.Repeatable; 25 import java.lang.annotation.Retention; 26 import java.lang.annotation.RetentionPolicy; 27 import java.lang.annotation.Target; 28 29 /** 30 * Indicates to the platform toolchain that there is an upcoming public SDK API change for a method. 31 * The API change will add a more specific return type in a subclass for an overridden method. 32 * 33 * <p>When this annotation is present, the toolchain is required to generate on-device bytecode for 34 * an overloaded implementation of the method which is marked as synthetic, returns the more 35 * specific type given in {@link CovariantReturnType#returnType()}, and which delegates to the 36 * method being annotated. 37 * 38 * <p>At some future point in time the public Android API can change so that the public API method 39 * returns the new type. Android platform developers can be sure that all releases after the API 40 * version specified in {@link CovariantReturnType#presentAfter()} have the new method signature on 41 * device and will therefore be compatible with code compiled against the newest public Android API 42 * stubs. 43 * 44 * <p>Once the actual method signature is updated to the new form and this annotation is removed 45 * there will be a synthetic overload for the method with the more general type provided (as normal) 46 * by the Java compiler ensuring compatibility with code compiled against the old stubs. 47 * 48 * <p>When adding this annotation to platform classes the developer should also add CTS tests to 49 * ensure the expected methods are present on all Android devices. 50 * 51 * <p>Notes on scope and limitations: 52 * <ul> 53 * <li>This annotation must have no effect on generated API stubs.</li> 54 * <li>This annotation does not allow the declared exceptions to be made more specific for the 55 * generated synthetic method. This could be added later.</li> 56 * <li>Any type parameters on the annotated method need not be copied.</li> 57 * <li>This annotation is <em>not</em> expected to be treated by the toolchain as inherited. All 58 * layers of platform class hierarchy must specify {@link CovariantReturnType} for all the overloads 59 * that have to be generated. The annotation is marked as repeatable for this reason.</li> 60 * </ul> 61 * 62 * @hide 63 */ 64 @Repeatable(CovariantReturnType.CovariantReturnTypes.class) 65 @Retention(RetentionPolicy.CLASS) 66 @Target({ ElementType.METHOD}) 67 @SystemApi(client = MODULE_LIBRARIES) 68 public @interface CovariantReturnType { 69 70 /** 71 * The return type of the synthetic method to generate. Must be a subclass of the return type 72 * of the method being annotated. 73 * 74 * @hide 75 */ 76 @SystemApi(client = MODULE_LIBRARIES) returnType()77 Class<?> returnType(); 78 79 /** 80 * The last Android API level not to have the generated synthetic method. The annotation can be 81 * removed and the actual return type updated when support for this API level is dropped. 82 * 83 * @hide 84 */ 85 @SystemApi(client = MODULE_LIBRARIES) presentAfter()86 int presentAfter(); 87 88 /** @hide */ 89 @Retention(RetentionPolicy.CLASS) 90 @Target({ElementType.METHOD}) 91 @SystemApi(client = MODULE_LIBRARIES) 92 @interface CovariantReturnTypes { 93 /** @hide */ 94 @SystemApi(client = MODULE_LIBRARIES) value()95 CovariantReturnType[] value(); 96 } 97 } 98