001/*
002 * Copyright (C) 2007 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package com.google.common.base;
018
019import static com.google.common.base.Preconditions.checkNotNull;
020
021import java.util.Collections;
022import java.util.HashMap;
023import java.util.Map;
024
025import javax.annotation.CheckReturnValue;
026import javax.annotation.Nullable;
027
028/**
029 * This class provides default values for all Java types, as defined by the JLS.
030 *
031 * @author Ben Yu
032 * @since 1.0
033 */
034@CheckReturnValue
035public final class Defaults {
036  private Defaults() {}
037
038  private static final Map<Class<?>, Object> DEFAULTS;
039
040  static {
041    // Only add to this map via put(Map, Class<T>, T)
042    Map<Class<?>, Object> map = new HashMap<Class<?>, Object>();
043    put(map, boolean.class, false);
044    put(map, char.class, '\0');
045    put(map, byte.class, (byte) 0);
046    put(map, short.class, (short) 0);
047    put(map, int.class, 0);
048    put(map, long.class, 0L);
049    put(map, float.class, 0f);
050    put(map, double.class, 0d);
051    DEFAULTS = Collections.unmodifiableMap(map);
052  }
053
054  private static <T> void put(Map<Class<?>, Object> map, Class<T> type, T value) {
055    map.put(type, value);
056  }
057
058  /**
059   * Returns the default value of {@code type} as defined by JLS --- {@code 0} for numbers, {@code
060   * false} for {@code boolean} and {@code '\0'} for {@code char}. For non-primitive types and
061   * {@code void}, {@code null} is returned.
062   */
063  @Nullable
064  public static <T> T defaultValue(Class<T> type) {
065    // Primitives.wrap(type).cast(...) would avoid the warning, but we can't use that from here
066    @SuppressWarnings("unchecked") // the put method enforces this key-value relationship
067    T t = (T) DEFAULTS.get(checkNotNull(type));
068    return t;
069  }
070}