com.google.common.base.Defaults Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of guava-core Show documentation
Durian - Guava's spikier (unofficial) cousin
The newest version!
/*
 * Original Guava code is copyright (C) 2015 The Guava Authors.
 * Modifications from Guava are copyright (C) 2015 DiffPlug.
 *
 * 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.CheckReturnValue;
import javax.annotation.Nullable;

/**
 * This class provides default values for all Java types, as defined by the JLS.
 *
 * @author Ben Yu
 * @since 1.0
 */
@CheckReturnValue
public final class Defaults {
	private Defaults() {}

	private static final Map, Object> DEFAULTS;

	static {
		// Only add to this map via put(Map, Class, T)
		Map, Object> map = new HashMap, 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  void put(Map, Object> map, Class 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}, {@code null} is returned.
	 */
	@Nullable
	public static  T defaultValue(Class 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;
	}
}