core/src/com/google/inject/spi/Dependency.java

/**
 * Copyright (C) 2008 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.spi;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.base.Objects;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Lists;
import com.google.inject.Key;

import java.util.List;
import java.util.Set;

/**
 * A variable that can be resolved by an injector.
 *
 * <p>Use {@link #get} to build a freestanding dependency, or {@link InjectionPoint} to build one
 * that's attached to a constructor, method or field.
 *
 * @author crazybob@google.com (Bob Lee)
 * @author jessewilson@google.com (Jesse Wilson)
 * @since 2.0
 */
public final class Dependency<T> {
  private final InjectionPoint injectionPoint;
  private final Key<T> key;
  private final boolean nullable;
  private final int parameterIndex;

  Dependency(InjectionPoint injectionPoint, Key<T> key, boolean nullable, int parameterIndex) {
    this.injectionPoint = injectionPoint;
    this.key = checkNotNull(key, "key");
    this.nullable = nullable;
    this.parameterIndex = parameterIndex;
  }

  /**
   * Returns a new dependency that is not attached to an injection point. The returned dependency is
   * nullable.
   */
  public static <T> Dependency<T> get(Key<T> key) {
    return new Dependency<T>(null, key, true, -1);
  }

  /**
   * Returns the dependencies from the given injection points.
   */
  public static Set<Dependency<?>> forInjectionPoints(Set<InjectionPoint> injectionPoints) {
    List<Dependency<?>> dependencies = Lists.newArrayList();
    for (InjectionPoint injectionPoint : injectionPoints) {
      dependencies.addAll(injectionPoint.getDependencies());
    }
    return ImmutableSet.copyOf(dependencies);
  }

  /**
   * Returns the key to the binding that satisfies this dependency.
   */
  public Key<T> getKey() {
    return this.key;
  }

  /**
   * Returns true if null is a legal value for this dependency.
   */
  public boolean isNullable() {
    return nullable;
  }

  /**
   * Returns the injection point to which this dependency belongs, or null if this dependency isn't
   * attached to a particular injection point.
   */
  public InjectionPoint getInjectionPoint() {
    return injectionPoint;
  }

  /**
   * Returns the index of this dependency in the injection point's parameter list, or {@code -1} if
   * this dependency does not belong to a parameter list. Only method and constuctor dependencies
   * are elements in a parameter list.
   */
  public int getParameterIndex() {
    return parameterIndex;
  }

  @Override public int hashCode() {
    return Objects.hashCode(injectionPoint, parameterIndex, key);
  }

  @Override public boolean equals(Object o) {
    if (o instanceof Dependency) {
      Dependency dependency = (Dependency) o;
      return Objects.equal(injectionPoint, dependency.injectionPoint)
          && Objects.equal(parameterIndex, dependency.parameterIndex)
          && Objects.equal(key, dependency.key);
    } else {
      return false;
    }
  }

  @Override public String toString() {
    StringBuilder builder = new StringBuilder();
    builder.append(key);
    if (injectionPoint != null) {
      builder.append("@").append(injectionPoint);
      if (parameterIndex != -1) {
        builder.append("[").append(parameterIndex).append("]");
      }
    }
    return builder.toString();
  }
}