core/src/com/google/inject/util/Types.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.util;

import com.google.inject.Provider;
import com.google.inject.internal.MoreTypes;
import com.google.inject.internal.MoreTypes.GenericArrayTypeImpl;
import com.google.inject.internal.MoreTypes.ParameterizedTypeImpl;
import com.google.inject.internal.MoreTypes.WildcardTypeImpl;
import java.lang.reflect.GenericArrayType;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.lang.reflect.WildcardType;
import java.util.Collection;
import java.util.List;
import java.util.Map;
import java.util.Set;

/**
 * Static methods for working with types.
 *
 * @author crazybob@google.com (Bob Lee)
 * @since 2.0
 */
public final class Types {
  private Types() {}

  /**
   * Returns a new parameterized type, applying {@code typeArguments} to {@code rawType}. The
   * returned type does not have an owner type.
   *
   * @return a {@link java.io.Serializable serializable} parameterized type.
   */
  public static ParameterizedType newParameterizedType(Type rawType, Type... typeArguments) {
    return newParameterizedTypeWithOwner(null, rawType, typeArguments);
  }

  /**
   * Returns a new parameterized type, applying {@code typeArguments} to {@code rawType} and
   * enclosed by {@code ownerType}.
   *
   * @return a {@link java.io.Serializable serializable} parameterized type.
   */
  public static ParameterizedType newParameterizedTypeWithOwner(
      Type ownerType, Type rawType, Type... typeArguments) {
    return new ParameterizedTypeImpl(ownerType, rawType, typeArguments);
  }

  /**
   * Returns an array type whose elements are all instances of {@code componentType}.
   *
   * @return a {@link java.io.Serializable serializable} generic array type.
   */
  public static GenericArrayType arrayOf(Type componentType) {
    return new GenericArrayTypeImpl(componentType);
  }

  /**
   * Returns a type that represents an unknown type that extends {@code bound}. For example, if
   * {@code bound} is {@code CharSequence.class}, this returns {@code ? extends CharSequence}. If
   * {@code bound} is {@code Object.class}, this returns {@code ?}, which is shorthand for {@code ?
   * extends Object}.
   */
  public static WildcardType subtypeOf(Type bound) {
    return new WildcardTypeImpl(new Type[] {bound}, MoreTypes.EMPTY_TYPE_ARRAY);
  }

  /**
   * Returns a type that represents an unknown supertype of {@code bound}. For example, if {@code
   * bound} is {@code String.class}, this returns {@code ? super String}.
   */
  public static WildcardType supertypeOf(Type bound) {
    return new WildcardTypeImpl(new Type[] {Object.class}, new Type[] {bound});
  }

  /**
   * Returns a type modelling a {@link List} whose elements are of type {@code elementType}.
   *
   * @return a {@link java.io.Serializable serializable} parameterized type.
   */
  public static ParameterizedType listOf(Type elementType) {
    return newParameterizedType(List.class, elementType);
  }

  /**
   * Returns a type modelling a {@link Collection} whose elements are of type {@code elementType}.
   *
   * @return a {@link java.io.Serializable serializable} parameterized type.
   */
  public static ParameterizedType collectionOf(Type elementType) {
    return newParameterizedType(Collection.class, elementType);
  }

  /**
   * Returns a type modelling a {@link Set} whose elements are of type {@code elementType}.
   *
   * @return a {@link java.io.Serializable serializable} parameterized type.
   */
  public static ParameterizedType setOf(Type elementType) {
    return newParameterizedType(Set.class, elementType);
  }

  /**
   * Returns a type modelling a {@link Map} whose keys are of type {@code keyType} and whose values
   * are of type {@code valueType}.
   *
   * @return a {@link java.io.Serializable serializable} parameterized type.
   */
  public static ParameterizedType mapOf(Type keyType, Type valueType) {
    return newParameterizedType(Map.class, keyType, valueType);
  }

  // for other custom collections types, use newParameterizedType()

  /**
   * Returns a type modelling a {@link Provider} that provides elements of type {@code elementType}.
   *
   * @return a {@link java.io.Serializable serializable} parameterized type.
   */
  public static ParameterizedType providerOf(Type providedType) {
    return newParameterizedType(Provider.class, providedType);
  }

  /**
   * Returns a type modelling a {@link javax.inject.Provider} that provides elements of type {@code
   * elementType}.
   *
   * @return a {@link java.io.Serializable serializable} parameterized type.
   */
  public static Type javaxProviderOf(Type type) {
    return Types.newParameterizedType(javax.inject.Provider.class, type);
  }
}