/**
* Copyright 2011-2015 John Ericksen
*
* 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 org.parceler;
/**
* @author John Ericksen
*/
public final class MapsUtil {
public static final String INITIAL_HASH_MAP_CAPACITY_METHOD = "initialHashMapCapacity";
private static final int MAX_POWER_OF_TWO = 1 << (Integer.SIZE - 2);
private MapsUtil() {
//
}
/**
* Copy of capacity method from Guava Maps utility.
*
* Returns a capacity that is sufficient to keep the map from being resized as long as it grows no
* larger than expectedSize and the load factor is ≥ its default (0.75).
*
* @param expectedSize
* @return HashMap capacity that avoids rehashing.
*/
public static int initialHashMapCapacity(int expectedSize) {
if (expectedSize < 0) {
throw new ParcelerRuntimeException("Expected size must be non-negative");
}
if (expectedSize < 3) {
return expectedSize + 1;
}
if (expectedSize < MAX_POWER_OF_TWO) {
// This is the calculation used in JDK8 to resize when a putAll
// happens; it seems to be the most conservative calculation we
// can make. 0.75 is the default load factor.
return (int) ((float) expectedSize / 0.75F + 1.0F);
}
return Integer.MAX_VALUE; // any large value
}
}