org.hibernate.util.CollectionHelper Maven / Gradle / Ivy
/*
* Hibernate, Relational Persistence for Idiomatic Java
*
* Copyright (c) 2008, Red Hat Middleware LLC or third-party contributors as
* indicated by the @author tags or express copyright attribution
* statements applied by the authors. All third-party contributions are
* distributed under license by Red Hat Middleware LLC.
*
* This copyrighted material is made available to anyone wishing to use, modify,
* copy, or redistribute it subject to the terms and conditions of the GNU
* Lesser General Public License, as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License
* for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this distribution; if not, write to:
* Free Software Foundation, Inc.
* 51 Franklin Street, Fifth Floor
* Boston, MA 02110-1301 USA
*/
package org.hibernate.util;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;
/**
* Various help for handling collections.
*
* @author Gavin King
* @author Steve Ebersole
*/
public final class CollectionHelper {
public static final int MINIMUM_INITIAL_CAPACITY = 16;
public static final float LOAD_FACTOR = 0.75f;
public static final List EMPTY_LIST = Collections.unmodifiableList( new ArrayList(0) );
public static final Collection EMPTY_COLLECTION = Collections.unmodifiableCollection( new ArrayList(0) );
public static final Map EMPTY_MAP = Collections.unmodifiableMap( new HashMap(0) );
private CollectionHelper() {
}
/**
* Build a properly sized map, especially handling load size and load factor to prevent immediate resizing.
*
* Especially helpful for copy map contents.
*
* @param size The size to make the map.
* @return The sized map.
*/
public static Map mapOfSize(int size) {
return new HashMap( determineProperSizing( size ), LOAD_FACTOR );
}
/**
* Given a map, determine the proper initial size for a new Map to hold the same number of values.
* Specifically we want to account for load size and load factor to prevent immediate resizing.
*
* @param original The original map
* @return The proper size.
*/
public static int determineProperSizing(Map original) {
return determineProperSizing( original.size() );
}
/**
* Given a set, determine the proper initial size for a new set to hold the same number of values.
* Specifically we want to account for load size and load factor to prevent immediate resizing.
*
* @param original The original set
* @return The proper size.
*/
public static int determineProperSizing(Set original) {
return determineProperSizing( original.size() );
}
/**
* Determine the proper initial size for a new collection in order for it to hold the given a number of elements.
* Specifically we want to account for load size and load factor to prevent immediate resizing.
*
* @param numberOfElements The number of elements to be stored.
* @return The proper size.
*/
public static int determineProperSizing(int numberOfElements) {
int actual = ( (int) (numberOfElements / LOAD_FACTOR) ) + 1;
return Math.max( actual, MINIMUM_INITIAL_CAPACITY );
}
public static List arrayList(int anticipatedSize) {
return new ArrayList( anticipatedSize );
}
}