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Java example source code file (OptionalBinderBinding.java)

This example Java source code file (OptionalBinderBinding.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

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Java - Java tags/keywords

binding, key, optionalbinderbinding

The OptionalBinderBinding.java Java example source code

/**
 * Copyright (C) 2014 Google Inc.
 *
 * 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 com.google.inject.multibindings;

import com.google.inject.Binding;
import com.google.inject.Key;
import com.google.inject.spi.Element;
import com.google.inject.spi.Elements;

/**
 * A binding for a OptionalBinder.
 * 
 * <p>Although OptionalBinders may be injected through a variety of types
 * {@code T}, {@code Optional<T>}, {@code Optional>}, etc..), an
 * OptionalBinderBinding exists only on the Binding associated with the
 * {@code Optional<T>} key.  Other bindings can be validated to be derived from this
 * OptionalBinderBinding using {@link #containsElement}.
 * 
 * @param <T> The fully qualified type of the optional binding, including Optional.
 *        For example: {@code Optional<String>}.
 * 
 * @since 4.0
 * @author sameb@google.com (Sam Berlin)
 */
public interface OptionalBinderBinding<T> {

  /** Returns the {@link Key} for this binding. */
  Key<T> getKey();
  
  /**
   * Returns the default binding (set by {@link OptionalBinder#setDefault}) if one exists or null
   * if no default binding is set. This will throw {@link UnsupportedOperationException} if it is
   * called on an element retrieved from {@link Elements#getElements}.
   * <p>
   * The Binding's type will always match the type Optional's generic type. For example, if getKey
   * returns a key of <code>Optional<String>, then this will always return a
   * <code>Binding<String>.
   */
  Binding<?> getDefaultBinding();
  
  /**
   * Returns the actual binding (set by {@link OptionalBinder#setBinding}) or null if not set.
   * This will throw {@link UnsupportedOperationException} if it is called on an element retrieved
   * from {@link Elements#getElements}.
   * <p>
   * The Binding's type will always match the type Optional's generic type. For example, if getKey
   * returns a key of <code>Optional<String>, then this will always return a
   * <code>Binding<String>.
   */
  Binding<?> getActualBinding();

  /**
   * Returns true if this OptionalBinder contains the given Element in order to build the optional
   * binding or uses the given Element in order to support building and injecting its data. This
   * will work for OptionalBinderBinding retrieved from an injector and
   * {@link Elements#getElements}. Usually this is only necessary if you are working with elements
   * retrieved from modules (without an Injector), otherwise {@link #getDefaultBinding} and
   * {@link #getActualBinding} are better options.
   */
  boolean containsElement(Element element);
}

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