/*
 * Copyright (c) 2011-2020, baomidou (jobob@qq.com).
 * <p>
 * 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
 * <p>
 * https://www.apache.org/licenses/LICENSE-2.0
 * <p>
 * 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.baomidou.mybatisplus.core.toolkit;

import java.util.Collection;
import java.util.HashMap;
import java.util.Map;
import java.util.function.Function;

/**
 * Collection工具类
 *
 * @author Caratacus
 * @since 2016-09-19
 */
public class CollectionUtils {

    private static final int MAX_POWER_OF_TWO = 1 << (Integer.SIZE - 2);

    /**
     * 校验集合是否为空
     *
     * @param coll 入参
     * @return boolean
     */
    public static boolean isEmpty(Collection<?> coll) {
        return (coll == null || coll.isEmpty());
    }

    /**
     * 校验集合是否不为空
     *
     * @param coll 入参
     * @return boolean
     */
    public static boolean isNotEmpty(Collection<?> coll) {
        return !isEmpty(coll);
    }

    /**
     * 判断Map是否为空
     *
     * @param map 入参
     * @return boolean
     */
    public static boolean isEmpty(Map<?, ?> map) {
        return (map == null || map.isEmpty());
    }

    /**
     * 判断Map是否不为空
     *
     * @param map 入参
     * @return boolean
     */
    public static boolean isNotEmpty(Map<?, ?> map) {
        return !isEmpty(map);
    }

    /**
     * 创建默认HashMap
     *
     * @param <K> K
     * @param <V> V
     * @return HashMap
     * @see com.google.common.collect.Maps#newHashMap()
     */
    public static <K, V> HashMap<K, V> newHashMap() {
        return new HashMap<>();
    }

    /**
     * 根据预期大小创建HashMap.
     *
     * @param expectedSize 预期大小
     * @param <K>          K
     * @param <V>          V
     * @return HashMap
     * @see com.google.common.collect.Maps#newHashMapWithExpectedSize
     */
    public static <K, V> HashMap<K, V> newHashMapWithExpectedSize(int expectedSize) {
        return new HashMap<>(capacity(expectedSize));
    }

    /**
     * 用来过渡下Jdk1.8下ConcurrentHashMap的性能bug
     * https://bugs.openjdk.java.net/browse/JDK-8161372
     *
     * @param concurrentHashMap ConcurrentHashMap 没限制类型了，非ConcurrentHashMap就别调用这方法了
     * @param key               key
     * @param mappingFunction   function
     * @param <K>               k
     * @param <V>               v
     * @return V
     * @since 3.3.3
     */
    public static <K, V> V computeIfAbsent(Map<K, V> concurrentHashMap, K key, Function<? super K, ? extends V> mappingFunction) {
        V v = concurrentHashMap.get(key);
        if (v != null) {
            return v;
        }
        return concurrentHashMap.computeIfAbsent(key, mappingFunction);
    }

    /**
     * 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).
     *
     * @see com.google.common.collect.Maps#capacity(int)
     */
    private static int capacity(int expectedSize) {
        if (expectedSize < 3) {
            if (expectedSize < 0) {
                throw new IllegalArgumentException("expectedSize cannot be negative but was: " + expectedSize);
            }
            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
    }
}

@@ -1854,16 +1854,36 @@
 shMap()%0A
+     * @since 3.3.3%0A
      */%0A
@@ -2197,16 +2197,36 @@
 tedSize%0A
+     * @since 3.3.3%0A
      */%0A
@@ -3329,16 +3329,36 @@
 ty(int)%0A
+     * @since 3.3.3%0A
      */%0A

标记版本.