Build a properly sized map, especially handling load size and load factor to prevent immediate resizing. - Java java.util

Java examples for java.util:Map Entry

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Description

Build a properly sized map, especially handling load size and load factor to prevent immediate resizing.

Demo Code

/*/*from ww w .  j a va  2  s  . co  m*/
 * 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 com.java2s;

import java.util.HashMap;

import java.util.Map;
import java.util.Set;

public class Main {
    public static void main(String[] argv) {
        int size = 42;
        System.out.println(mapOfSize(size));
    }

    public static final int MINIMUM_INITIAL_CAPACITY = 16;
    public static final float LOAD_FACTOR = 0.75f;

    /**
     * Build a properly sized map, especially handling load size and load factor to prevent immediate resizing.
     * <p/>
     * 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);
    }
}

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