1 /* 2 * Copyright (C) 2007 The Guava Authors 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package com.google.common.base; 18 19 import static com.google.common.base.Preconditions.checkNotNull; 20 21 import java.util.Collections; 22 import java.util.HashMap; 23 import java.util.Map; 24 25 import javax.annotation.Nullable; 26 27 /** 28 * This class provides default values for all Java types, as defined by the JLS. 29 * 30 * @author Ben Yu 31 * @since 1.0 32 */ 33 public final class Defaults { 34 private Defaults() {} 35 36 private static final Map<Class<?>, Object> DEFAULTS; 37 38 static { 39 // Only add to this map via put(Map, Class<T>, T) 40 Map<Class<?>, Object> map = new HashMap<Class<?>, Object>(); 41 put(map, boolean.class, false); 42 put(map, char.class, '\0'); 43 put(map, byte.class, (byte) 0); 44 put(map, short.class, (short) 0); 45 put(map, int.class, 0); 46 put(map, long.class, 0L); 47 put(map, float.class, 0f); 48 put(map, double.class, 0d); 49 DEFAULTS = Collections.unmodifiableMap(map); 50 } 51 52 private static <T> void put(Map<Class<?>, Object> map, Class<T> type, T value) { 53 map.put(type, value); 54 } 55 56 /** 57 * Returns the default value of {@code type} as defined by JLS --- {@code 0} for numbers, {@code 58 * false} for {@code boolean} and {@code '\0'} for {@code char}. For non-primitive types and 59 * {@code void}, null is returned. 60 */ 61 @Nullable 62 public static <T> T defaultValue(Class<T> type) { 63 // Primitives.wrap(type).cast(...) would avoid the warning, but we can't use that from here 64 @SuppressWarnings("unchecked") // the put method enforces this key-value relationship 65 T t = (T) DEFAULTS.get(checkNotNull(type)); 66 return t; 67 } 68 } 69
