com.alibaba.excel.util.MapUtils Maven / Gradle / Ivy
package com.alibaba.excel.util;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.TreeMap;
/**
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.
*
* @author Apache Software Foundation (ASF)
*/
public class MapUtils {
private MapUtils() {}
/**
* Creates a mutable, empty {@code HashMap} instance.
*
* Note: if mutability is not required, use ImmutableMap.of() instead.
*
*
Note: if {@code K} is an {@code enum} type, use newEnumMap instead.
*
*
Note for Java 7 and later: this method is now unnecessary and should be treated as
* deprecated. Instead, use the {@code HashMap} constructor directly, taking advantage of the new
* "diamond" syntax.
*
* @return a new, empty {@code HashMap}
*/
public static HashMap newHashMap() {
return new HashMap<>(16);
}
/**
* Creates a mutable, empty {@code TreeMap} instance using the natural ordering of its
* elements.
*
* Note: if mutability is not required, use ImmutableSortedMap.of() instead.
*
*
Note for Java 7 and later: this method is now unnecessary and should be treated as
* deprecated. Instead, use the {@code TreeMap} constructor directly, taking advantage of the new
* "diamond" syntax.
*
* @return a new, empty {@code TreeMap}
*/
public static TreeMap newTreeMap() {
return new TreeMap<>();
}
/**
* Creates a {@code HashMap} instance, with a high enough "initial capacity" that it should
* hold {@code expectedSize} elements without growth. This behavior cannot be broadly guaranteed,
* but it is observed to be true for OpenJDK 1.7. It also can't be guaranteed that the method
* isn't inadvertently oversizing the returned map.
*
* @param expectedSize the number of entries you expect to add to the returned map
* @return a new, empty {@code HashMap} with enough capacity to hold {@code expectedSize} entries
* without resizing
* @throws IllegalArgumentException if {@code expectedSize} is negative
*/
public static HashMap newHashMapWithExpectedSize(int expectedSize) {
return new HashMap<>(capacity(expectedSize));
}
/**
* Creates a mutable, empty, insertion-ordered {@code LinkedHashMap} instance.
*
* Note: if mutability is not required, use ImmutableMap.of() instead.
*
*
Note for Java 7 and later: this method is now unnecessary and should be treated as
* deprecated. Instead, use the {@code LinkedHashMap} constructor directly, taking advantage of
* the new "diamond" syntax.
*
* @return a new, empty {@code LinkedHashMap}
*/
public static LinkedHashMap newLinkedHashMap() {
return new LinkedHashMap<>();
}
/**
* Creates a {@code LinkedHashMap} instance, with a high enough "initial capacity" that it
* should hold {@code expectedSize} elements without growth. This behavior cannot be
* broadly guaranteed, but it is observed to be true for OpenJDK 1.7. It also can't be guaranteed
* that the method isn't inadvertently oversizing the returned map.
*
* @param expectedSize the number of entries you expect to add to the returned map
* @return a new, empty {@code LinkedHashMap} with enough capacity to hold {@code expectedSize}
* entries without resizing
* @throws IllegalArgumentException if {@code expectedSize} is negative
* @since 19.0
*/
public static LinkedHashMap newLinkedHashMapWithExpectedSize(int expectedSize) {
return new LinkedHashMap<>(capacity(expectedSize));
}
/**
* 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).
*/
static int capacity(int expectedSize) {
if (expectedSize < 3) {
return expectedSize + 1;
}
if (expectedSize < IntUtils.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;
}
}