1 /* 2 * Copyright (C) 2008 Google Inc. 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 com.google.inject; 18 19 import com.google.inject.spi.BindingScopingVisitor; 20 import com.google.inject.spi.BindingTargetVisitor; 21 import com.google.inject.spi.Element; 22 23 /** 24 * A mapping from a key (type and optional annotation) to the strategy for getting instances of the 25 * type. This interface is part of the introspection API and is intended primarily for use by tools. 26 * 27 * <p>Bindings are created in several ways: 28 * 29 * <ul> 30 * <li>Explicitly in a module, via {@code bind()} and {@code bindConstant()} statements: 31 * <pre> 32 * bind(Service.class).annotatedWith(Red.class).to(ServiceImpl.class); 33 * bindConstant().annotatedWith(ServerHost.class).to(args[0]);</pre> 34 * 35 * <li>Implicitly by the Injector by following a type's {@link ImplementedBy pointer} {@link 36 * ProvidedBy annotations} or by using its {@link Inject annotated} or default constructor. 37 * <li>By converting a bound instance to a different type. 38 * <li>For {@link Provider providers}, by delegating to the binding for the provided type. 39 * </ul> 40 * 41 * <p>They exist on both modules and on injectors, and their behaviour is different for each: 42 * 43 * <ul> 44 * <li><strong>Module bindings</strong> are incomplete and cannot be used to provide instances. This 45 * is because the applicable scopes and interceptors may not be known until an injector is 46 * created. From a tool's perspective, module bindings are like the injector's source code. They 47 * can be inspected or rewritten, but this analysis must be done statically. 48 * <li><strong>Injector bindings</strong> are complete and valid and can be used to provide 49 * instances. From a tools' perspective, injector bindings are like reflection for an injector. 50 * They have full runtime information, including the complete graph of injections necessary to 51 * satisfy a binding. 52 * </ul> 53 * 54 * @param <T> the bound type. The injected is always assignable to this type. 55 * @author crazybob@google.com (Bob Lee) 56 * @author jessewilson@google.com (Jesse Wilson) 57 */ 58 public interface Binding<T> extends Element { 59 60 /** Returns the key for this binding. */ getKey()61 Key<T> getKey(); 62 63 /** 64 * Returns the scoped provider guice uses to fulfill requests for this binding. 65 * 66 * @throws UnsupportedOperationException when invoked on a {@link Binding} created via {@link 67 * com.google.inject.spi.Elements#getElements}. This method is only supported on {@link 68 * Binding}s returned from an injector. 69 */ getProvider()70 Provider<T> getProvider(); 71 72 /** 73 * Accepts a target visitor. Invokes the visitor method specific to this binding's target. 74 * 75 * @param visitor to call back on 76 * @since 2.0 77 */ acceptTargetVisitor(BindingTargetVisitor<? super T, V> visitor)78 <V> V acceptTargetVisitor(BindingTargetVisitor<? super T, V> visitor); 79 80 /** 81 * Accepts a scoping visitor. Invokes the visitor method specific to this binding's scoping. 82 * 83 * @param visitor to call back on 84 * @since 2.0 85 */ acceptScopingVisitor(BindingScopingVisitor<V> visitor)86 <V> V acceptScopingVisitor(BindingScopingVisitor<V> visitor); 87 } 88