1 /* 2 * Copyright (C) 2016 The Dagger Authors. 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 dagger; 18 19 import static java.lang.annotation.ElementType.METHOD; 20 import static java.lang.annotation.ElementType.PARAMETER; 21 import static java.lang.annotation.RetentionPolicy.RUNTIME; 22 23 import dagger.internal.Beta; 24 import java.lang.annotation.Documented; 25 import java.lang.annotation.Retention; 26 import java.lang.annotation.Target; 27 28 /** 29 * Marks a method on a {@linkplain Component.Builder component builder} or a parameter on a 30 * {@linkplain Component.Factory component factory} as binding an instance to some key within the 31 * component. 32 * 33 * <p>For example: 34 * 35 * <pre> 36 * {@literal @Component.Builder} 37 * interface Builder { 38 * {@literal @BindsInstance} Builder foo(Foo foo); 39 * {@literal @BindsInstance} Builder bar({@literal @Blue} Bar bar); 40 * ... 41 * } 42 * 43 * // or 44 * 45 * {@literal @Component.Factory} 46 * interface Factory { 47 * MyComponent newMyComponent( 48 * {@literal @BindsInstance} Foo foo, 49 * {@literal @BindsInstance @Blue} Bar bar); 50 * } 51 * </pre> 52 * 53 * <p>will allow clients of the builder or factory to pass their own instances of {@code Foo} and 54 * {@code Bar}, and those instances can be injected within the component as {@code Foo} or 55 * {@code @Blue Bar}, respectively. It's important to note that unlike in factories, the methods in 56 * builders should only accept and bind a single parameter each. Using the following will result in 57 * an error: 58 * 59 * <pre> 60 * {@literal @Component.Builder} 61 * interface Builder { 62 * // Error! Builder methods can only have one parameter 63 * {@literal @BindsInstance} Builder fooAndBar(Foo foo, {@literal @Blue} Bar bar); 64 * ... 65 * } 66 * </pre> 67 * 68 * <p>{@code @BindsInstance} arguments may not be {@code null} unless the parameter is annotated 69 * with {@code @Nullable}. 70 * 71 * <p>For builders, {@code @BindsInstance} methods must be called before building the component, 72 * unless their parameter is marked {@code @Nullable}, in which case the component will act as 73 * though it was called with a {@code null} argument. Primitives, of course, may not be marked 74 * {@code @Nullable}. 75 * 76 * <p>Binding an instance is equivalent to passing an instance to a module constructor and providing 77 * that instance, but is often more efficient. When possible, binding object instances should be 78 * preferred to using module instances. 79 */ 80 @Documented 81 @Retention(RUNTIME) 82 @Target({METHOD, PARAMETER}) 83 @Beta 84 public @interface BindsInstance {} 85