content: /*
   * Copyright (C) 2011 The Android Open Source Project
   *
   * 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.android.internal.util;
  
  /**
   * Simple static methods to be called at the start of your own methods to verify
   * correct arguments and state.
   */
  public 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; will
       *                     be converted to a string using {@link String#valueOf(Object)}
       * @return the non-null reference that was validated
       * @throws NullPointerException if {@code reference} is null
       */
      public static <T> T checkNotNull(T reference, Object errorMessage) {
          if (reference == null) {
              throw new NullPointerException(String.valueOf(errorMessage));
          }
          return reference;
      }
  
      /**
       * Ensures the truth of an expression involving the state of the calling
       * instance, but not involving any parameters to the calling method.
       *
       * @param expression a boolean expression
       * @throws IllegalStateException if {@code expression} is false
       */
      public static void checkState(boolean expression) {
          if (!expression) {
              throw new IllegalStateException();
          }
      }
  }
  