/*
    * Copyright (C) 2007 The Guava 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 com.google.common.base;
  
  import static com.google.common.base.Preconditions.checkNotNull;
  
  import java.util.Collections;
  import java.util.HashMap;
  import java.util.Map;
  
  import javax.annotation.Nullable;
  
  /**
   * This class provides default values for all Java types, as defined by the JLS.
   *
   * @author Ben Yu
   * @since 1.0
   */
  public final class Defaults {
    private Defaults() {}
  
    private static final Map<Class<?>, Object> DEFAULTS;
  
    static {
      // Only add to this map via put(Map, Class<T>, T)
      Map<Class<?>, Object> map = new HashMap<Class<?>, Object>();
      put(map, boolean.class, false);
      put(map, char.class, '\0');
      put(map, byte.class, (byte) 0);
      put(map, short.class, (short) 0);
      put(map, int.class, 0);
      put(map, long.class, 0L);
      put(map, float.class, 0f);
      put(map, double.class, 0d);
      DEFAULTS = Collections.unmodifiableMap(map);
    }
  
    private static <T> void put(Map<Class<?>, Object> map, Class<T> type, T value) {
      map.put(type, value);
    }
  
    /**
     * Returns the default value of {@code type} as defined by JLS --- {@code 0} for numbers, {@code
     * false} for {@code boolean} and {@code '\0'} for {@code char}. For non-primitive types and
     * {@code void}, null is returned.
     */
    @Nullable
    public static <T> T defaultValue(Class<T> type) {
      // Primitives.wrap(type).cast(...) would avoid the warning, but we can't use that from here
      @SuppressWarnings("unchecked") // the put method enforces this key-value relationship
      T t = (T) DEFAULTS.get(checkNotNull(type));
      return t;
    }
  }