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