java/dagger/internal/Preconditions.java

/*
 * Copyright (C) 2016 The Dagger Authors.
 *
 * 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 dagger.internal;

/**
 * An adaptation of Guava's {@code com.google.common.base.Preconditions} that is specially tailored
 * to support checks applied in Dagger's generated code.
 */
public final class Preconditions {
  /**
   * Ensures that an object reference passed as a parameter to the calling method is not null.
   *
   * @param reference an object reference
   * @return the non-null reference that was validated
   * @throws NullPointerException if {@code reference} is null
   */
  public static <T> T checkNotNull(T reference) {
    if (reference == null) {
      throw new NullPointerException();
    }
    return reference;
  }

  /**
   * Ensures that an object reference passed as a parameter to the calling method is not null.
   *
   * @param reference an object reference
   * @param errorMessage the exception message to use if the check fails
   * @return the non-null reference that was validated
   * @throws NullPointerException if {@code reference} is null
   */
  public static <T> T checkNotNull(T reference, String errorMessage) {
    if (reference == null) {
      throw new NullPointerException(errorMessage);
    }
    return reference;
  }

  /**
   * Ensures that an object reference returned from a provides method is not null.
   *
   * @param reference an object reference
   * @return the non-null reference that was validated
   * @throws NullPointerException if {@code reference} is null
   */
  public static <T> T checkNotNullFromProvides(T reference) {
    if (reference == null) {
      throw new NullPointerException("Cannot return null from a non-@Nullable @Provides method");
    }
    return reference;
  }

  /**
   * Ensures that an object reference returned from a component method is not null.
   *
   * @param reference an object reference
   * @return the non-null reference that was validated
   * @throws NullPointerException if {@code reference} is null
   */
  public static <T> T checkNotNullFromComponent(T reference) {
    if (reference == null) {
      throw new NullPointerException("Cannot return null from a non-@Nullable component method");
    }
    return reference;
  }

  /**
   * Ensures that an object reference passed as a parameter to the calling method is not null.
   *
   * @param reference an object reference
   * @param errorMessageTemplate a template for the exception message should the check fail. The
   *     message is formed by replacing the single {@code %s} placeholder in the template with
   *     {@code errorMessageArg}.
   * @param errorMessageArg the argument to be substituted into the message template. Converted to a
   *     string using {@link String#valueOf(Object)}, except for {@link Class} objects, which use
   *     {@link Class#getCanonicalName()}.
   * @return the non-null reference that was validated
   * @throws NullPointerException if {@code reference} is null
   * @throws IllegalArgumentException if {@code errorMessageTemplate} doesn't contain exactly one
   *     "%s"
   */
  public static <T> T checkNotNull(
      T reference, String errorMessageTemplate, Object errorMessageArg) {
    if (reference == null) {
      // Simple implementation of String.format, which is not GWT-compatible
      if (!errorMessageTemplate.contains("%s")) {
        throw new IllegalArgumentException("errorMessageTemplate has no format specifiers");
      }
      if (errorMessageTemplate.indexOf("%s") != errorMessageTemplate.lastIndexOf("%s")) {
        throw new IllegalArgumentException(
            "errorMessageTemplate has more than one format specifier");
      }
      String argString =
          errorMessageArg instanceof Class
              ? ((Class) errorMessageArg).getCanonicalName()
              : String.valueOf(errorMessageArg);
      throw new NullPointerException(errorMessageTemplate.replace("%s", argString));
    }
    return reference;
  }

  /**
   * Checks that the component builder field {@code requirement} has been initialized.
   *
   * @throws IllegalStateException if {@code requirement is null}
   */
  public static <T> void checkBuilderRequirement(T requirement, Class<T> clazz) {
    if (requirement == null) {
      throw new IllegalStateException(clazz.getCanonicalName() + " must be set");
    }
  }

  private Preconditions() {}
}