java hashmap example

First, HashMap1. Format:hashmapExample: hashmap2. Methods(1) Put (key, value); When key repeats, only the last value assigned to key is obtainedExample: Map.put ("Key1", "Hello");(2) get ();Example: Map.get ("Key1");(3) Putall ();(4) remove ();3. Traverse(1) Iterative traversalExample: SetInteratorwhile (Iter.hasnext ()) {String kv = Iter.next ();String v = map.get ();System.out.println (v);}(2) for each () traversalExample: for (String Kv:keyset) {SY

;threshold) - resize (); Wu afternodeinsertion (evict); - return NULL; About}1.3.2 Pop Returns null if there is a current key in the HashMap and returns its corresponding value JDK1.8 version source code is as follows:1 /**2 * Returns the value to which the specified key is mapped,3 * or {@codeNULL} If this maps contains no mapping for the key.4 *5 * 6 * {@codek} to a value {@codeV} such that {@code(key==null? K==nu

Time Angle: Hashtable * @since JDK1.0 ; HashMap * @since 1.2base class and interface angle:public class HashtableExtends dictionaryImplements Mappublic class HashmapExtends abstractmapImplements MapImplements the same interface, inheriting from different base classes (dictionaries) dictionaryThread-Safe angle:Hashmap.java:* * If Multiple threads access a hash map concurrently, and at least one of* The threads modifies the map structurally, it * Sy

prefix, int phoneNumber) { this.prefix = prefix; this.phoneNumber = phoneNumber; } @Override public boolean equals(Object o) { if(this == o) { return true; } if(!(o instanceof PhoneNumber)) { return false; } PhoneNumber pn = (PhoneNumber)o; return pn.prefix == prefix pn.phoneNumber == phoneNumber; } @Override public int hashCode() { int result = 17; result = 31 *

HashMap and Linkedhashmap are two implementation classes of the map interface, the biggest difference is that hashmap elements are stored in order, and the elements of Linkedhashmap are stored in an orderly manner, example:mapOutput Result:Hashmap3:32:21:10:07:76:65:54:49:98:8linkedhashmap0:01:12:23:34:45:56:67:78:89:9Previously also published a book to achieve the order of the map elements "

The value of HashMap is not sequential, it is implemented according to the hashcode of key. How are we going to achieve this sort of unordered hashmap? (TreeMap similar)Import Java.util.arraylist;import java.util.arrays;import Java.util.collections;import Java.util.Comparator;import Java.util.hashmap;import Java.util.list;import Java.util.map;import java.util.Map.Entry; mapOperation Result:e:55555d:44444c:3

1. In the array we index the content by the array subscript, and in the map we index the object by object, the object to index is called key, and its corresponding object is called value. Two methods of 2.HASHMAP traversal, either through the Set1. Traversing through the keyset collection set hashmap.keyset (); Iterator ketset.iterator (); while (Keyiterator.hasnext ()) { object = keyiterator.next ();

Class:public class HashMap Inherited from Abstractmap implements the Map,cloneable,serializable interface Can be serialized Can be clone //默认初始容量为16static final int DEFAULT_INITIAL_CAPACITY = 1 InitializationMap New Hashmap Initialcapacity to 0xB Loadfactor defaults to 0.75 The first step is to determine if the value of initialcapacity is less than 0 or greater tha

relationships, it returnsNULL. (ReturnNULLIt may also indicate that the mapping was preceded by aNULLwith theKeyAssociation. )7.putAllpublic void Putall (mapSpecifies that all mappings of mappings are copied to this map8.removePublic V Remove (Object key);removes the mapping of the specified key (if any) from this map. The return value iswith theKeythe old value of the association;Keydoes not have any mapping relationships, it returnsNULL. (ReturnNULLIt may also indicate that the mapping was pr

Array Array (array) and vector are very similar Java artifacts (constructs), which are completely different and should be determined according to their functions when choosing to use them. 1, array: Java arrays elements can not be subscript out of bounds, to a large extent, to ensure the security of Java programs, and other languages appear this problem often lea

Package com.hephec.Map;Import Java.util.HashMap;Import java.util.Hashtable;Import Java.util.Iterator;Import Java.util.Map;Import Java.util.TreeMap;Class Hahsmaps{public static void Main (string[] args){MapMap.put ("A", "AAA");Map.put ("B", "BBB");Map.put ("C", "CCC");Map.put ("D", "ddd");Iteratorwhile (Iterator.hasnext ()) {Object Key=iterator.next ();System.out.println ("Map.get (Key) is:" +map.get (key));}Define Hashtable, which is used to testHashtableTab.put ("A", "AAA");Tab.put ("B", "BBB")

= = Hash ((k= e.key) = = Key | | (Key! =NULLKey.equals (k)))) returne; } while((E = e.next)! =NULL); } } return NULL; }1. First determine if table[] is empty, determine whether the table[index is empty by hashing the index, or null if any of the entries is empty.2. Determine table[index] hash and key are all the same as the lookup, if the hash and key are the same, then directly return to the table[index].if // Always Check first node null key.equals (k

HashMap>>>: Move right^: Bitwise XOR OR: Logic andFinal V putval (int hash, K key, V value, Boolean onlyifabsent, nbsp; Boolean evict) { nodeeach time you put an element into HashMap, a node object is new, and the position is determined by calculating the hashcode value of the key. If two elements have the same hashcode, they will be placed on the same index. The problem arises, how do you put it? Originall

This is a creation in Article, where the information may have evolved or changed. Performance comparison Insert 10 million records to compare memory usage size and insertion time. Test machine configuration Intel (R) Core (TM) i3-4000m CPU @2.40ghz 2.40GHz 12.0GB Memory Front-facing conditions Go, avoid the memory copy when expanding capacity, the size of the initialization volume is 13333333. Make (map[int]int,13333333) Java, avoid memory copy when e

　1. Introduction through an essay above we know that the bottom of hashset is implemented by map, so what is map? How is the bottom layer implemented? Here we analyze the source code, to see the specific structure and implementation. The Map collection class is used to store element pairs (called "Keys" and "values"), where each key is mapped to a value. Map.entry is its inner class, which describes the key/value pairs in the map. It should be noted that the map, which allows NULL for a key, als

longer executed.(2) But in the case of a hash collision, the first two conditions are established, and then the last equals must be used to determine the equality of the objects.A 3.hash collision scene?(1) Generally appears in large data situations(2) The generation method of Hashcode is weak (such as the artificial production hashcode above)Summary: This chapter mainly through the introduction of hash collision once again in-depth understanding of hashmap