    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
    017    package com.google.common.base;
    018
    019    import java.util.Collections;
    020    import java.util.HashMap;
    021    import java.util.Map;
    022
    023    /**
    024     * This class provides default values for all Java types, as defined by the JLS.
    025     *
    026     * @author Ben Yu
    027     * @since 1.0
    028     */
    029    public final class Defaults {
    030      private Defaults() {}
    031
    032      private static final Map<Class<?>, Object> DEFAULTS;
    033
    034      static {
    035        Map<Class<?>, Object> map = new HashMap<Class<?>, Object>();
    036        put(map, boolean.class, false);
    037        put(map, char.class, '\0');
    038        put(map, byte.class, (byte) 0);
    039        put(map, short.class, (short) 0);
    040        put(map, int.class, 0);
    041        put(map, long.class, 0L);
    042        put(map, float.class, 0f);
    043        put(map, double.class, 0d);
    044        DEFAULTS = Collections.unmodifiableMap(map);
    045      }
    046
    047      private static <T> void put(Map<Class<?>, Object> map, Class<T> type, T value) {
    048        map.put(type, value);
    049      }
    050
    051      /**
    052       * Returns the default value of {@code type} as defined by JLS --- {@code 0} for numbers, {@code
    053       * false} for {@code boolean} and {@code '\0'} for {@code char}. For non-primitive types and
    054       * {@code void}, null is returned.
    055       */
    056      @SuppressWarnings("unchecked")
    057      public static <T> T defaultValue(Class<T> type) {
    058        return (T) DEFAULTS.get(type);
    059      }
    060    }