HashMap Class: a basic key-value map where the elements are unordered : 哈希映射 « 集合 « Java 教程

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Java 教程 » 集合 » 哈希映射

9. 25. 1. HashMap Class: a basic key-value map where the elements are unordered

A Map is a storage that hold key to value mappings. There cannot be duplicate keys in a Map and each key maps to at most one value. HashMap is unsynchronized and Hashtable is synchronized. HashMap is the faster one between the two. If you need to maintain map keys in an ordered fashion, you can use TreeMap.

Creating a HashMap


public HashMap()

public HashMap(int initialCapacity)

public HashMap(int initialCapacity, float loadFactor)

The fourth constructor is the standard copy constructor, which creates a new HashMap from another map:


public HashMap(Map map)

9. 25. 哈希映射
	9. 25. 1.	HashMap Class: a basic key-value map where the elements are unordered
	9. 25. 2.	遍历HashMap的值
	9. 25. 3.	得到同步映射从HashMap
	9. 25. 4.	检查在HashMap是否存在特定的键
	9. 25. 5.	在HashMap中检查特定的值
	9. 25. 6.	映射的键值
	9. 25. 7.	映射的值
	9. 25. 8.	映射的值和映射
	9. 25. 9.	存储原始类型的集合
	9. 25. 10.	获取HashMap的键值
	9. 25. 11.	获取HashMap的尺寸
	9. 25. 12.	Adding Key-Value Pairs: public Object put(Object key, Object value)
	9. 25. 13.	如果键值不存在，添加
	9. 25. 14.	Unlike a Hashtable, both the key and the value for a HashMap can be null
	9. 25. 15.	To copy all the key-value pairs from one Map into another: public void putAll(Map map)
	9. 25. 16.	展示内容
	9. 25. 17.	删除值从HashMap
	9. 25. 18.	删除键和值的配对
	9. 25. 19.	清除所有的内容从映射
	9. 25. 20.	Sizing Hash Maps: find out the number of key-value pairs within the HashMap
	9. 25. 21.	Fetching Keys and Values: find a value based upon a specific key with: public Object get(Object key)
	9. 25. 22.	Getting the set of all keys with the keySet() method: public Set keySet()
	9. 25. 23.	To get the set of all the values in the hash map: public Collection values()
	9. 25. 24.	To get a set of Map.Entry elements back from a HashMap: public Set entrySet()
	9. 25. 25.	查找元素
	9. 25. 26.	克隆散列映射
	9. 25. 27.	Creating a Copy of a Collection: the objects are not cloned.
	9. 25. 28.	Checking Hash Maps for Equality: public boolean equals(Object o)
	9. 25. 29.	排序HashMap依据键值
	9. 25. 30.	序列化哈希集
	9. 25. 31.	使用迭代循环
	9. 25. 32.	从HashMap创建的Java哈希表
	9. 25. 33.	How do I...Store simple pairs of data for quick lookup?

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