custom hashmap in java

This is a classic problem in Java and is often asked in interviews. In fact, a lot of books or articles have mentioned to Overload hashcode () and Equals () two methods to implement a custom key in the HashMap search, but why and if not to do this will have the consequences, as if very little an article, so write an article to explain. First of all, if we direct

); System.out.println (P.equals (q)); System.out.println (P.hashcode ()+ " " +Q.hashcode ()); MapNewHashMap (); Map.put (P,1); System.out.println (Map.containskey (q)); Map.put (q,2); for(pairKey:map.keySet ()) {System.out.println (Map.get (key)); } }}Then the result of removing the note is:True195 195True2Although there is no reason to say that the hashcode overload here, but at least the same value of two objects their hashcode is the same, so that in

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 *

different sets of elements of the operation of the same type, increase, delete, check ...In this example, there are two ways to take an element, either keyset, or .... Show keyset first.The set set contains the key type,In fact, the way of writing here is very strange, from the distance, lisi,38 and Beijing three attributes in the collection, the writing method is rather strange, did not read.The hash is unordered and the output is unordered.Now modify the program, for Zhaoliu This object, modi

The HashMap class in the Java set and the HashMap class in the Java set Jdk1.8.0 _ 144 As one of the most common collections, HashMap inherits from AbstractMap. The HashMap Implementation of JDK 8 is different from that of JDK 7.

Java Collection --- HashMap source code analysis, java --- hashmap source code 1. HashMap Overview HashMap is implemented based on the Map interface of the hash table. This implementation provides all optional ing operations and a

Java Collection series [3] ---- HashMap source code analysis, java ---- hashmap We have analyzed the ArrayList and ArrayList sets. We know that ArrayList is implemented based on arrays, and ArrayList is implemented based on linked lists. They each have their own advantages and disadvantages. For example, ArrayList is s

HashMapis a very powerful data structure in Java. We use it everyday and almost in all applications. There is quite a few examples which I had written before on what to Implement Threadsafe cache, how to convert Hashmap to Arraylist?We used Hashmap in both above examples but those is pretty simple use cases of Hashmap.

Java. util. HashMap, java. util. hashmap HashMap is one of the most commonly used classes. It implements the hash algorithm. Although it is easy to use, there are many points worth studying. HashMap stores key-value pairs in the f

Java Collection: HashMap source code analysis, hashmap source code1. HashMap Overview HashMap is implemented based on the Map interface of the hash table. This implementation provides all optional ing operations and allows the use of null values and null keys. (Except for no

() because if key object return different hashcode during insertion and RetrievalThan it won't be possible to get object from hashmap. immutability is best as it offers other advantages as well likethread-safety, if you can keep your hashcodeSame by only making certain fieldsfinal, then you go for that as well. Since equals () and hashcode () method is used during reterival of value object from hashmap,Its

The comparison between HashMap and Hashtable is a common problem in the Java interview to test whether the programmer can use the collection class correctly and whether it can be used in a variety of ways to solve problems. The work of HashMap, the comparison of ArrayList with vectors, and the problem are the most classic questions about the

In the JDK1.5 there is a for loop of the traversal of the wording, now should no one use JDK1.4 it? I see those 2005 Java Books, rectification series of Java books are used JDK1.5, of course JDK1.7 has been used, it is said that JDK1.7 is compatible jdk1.2~jdk1.7, now Java programming is based on JDK1.5. However, because the exam is not required or any other reas

Java -- HashMap implementation principle, self-implemented simple HashMap, javahashmap There are arrays and linked lists in the data structure to store data. However, the array storage range is continuous, addressing is easy, and insertion and deletion are difficult. The linked list space is discrete, therefore, addressing is difficult, and insertion and deletio

There are arrays and linked lists in the data structure to achieve the storage, but the array storage interval is continuous, easy to address, insert and delete difficult, and the list of the space is discrete, so addressing difficulties, insert and delete easy.Therefore, combining the advantages of both, we can design a data structure-a hash table (hash table), it is easy to address, insert and delete. In Java, the implementation of the hash table is

student:" +scores.size ()); -SYSTEM.OUT.PRINTLN ("scores is" + (Scores.isempty ()? " Empty ":" Not Empty ")); - in //Traverse and delete target, cost less -iteratorScores.entryset (). iterator (); to for(; Begit.hasnext ();) { +map.entryBegit.next (); - the if(Item.getvalue () = = 100.0) { * Begit.remove (); $ }Panax Notoginseng } - the System.out.println (scores); + A scores.clear (); theSYSTEM.OUT.PRINTLN (scores);The output is as follows:{

1. Case of HashMap Collection (hashmapHashmapKey: StudentRequirement: If the member variable values for two objects are the same, then the same object.Value: StringHashMap is the most commonly used map collection, and its key-value pairs are stored with the hash code of the key to determine where the value is placed.An object that is a key in HashMap must override the Hashcode () method of object and the Eq

//add basic classes to a large collection -Czbkmap.put ("JY", jymap); the + //iterating through the collection ASetCzbkmap.keyset (); the for(String czbkmapkey:czbkmapset) { + System.out.println (czbkmapkey); -hashmapCzbkmap.get (czbkmapkey); $SetCzbkmapvalue.keyset (); $ for(String czbkmapvaluekey:czbkmapvalueset) { -Integer Czbkmapvaluevalue =Czbkmapvalue.get (czbkmapvaluekey); -System.out.println ("\ T" +czbkmapvaluekey+ "---" +czbkmapvaluevalue

I. Overview of HashMap HashMap is an asynchronous implementation based on the map interface of a hash table. This implementation provides all the optional mapping operations and allows NULL values and NULL keys to be used. This class does not guarantee the order of mappings, especially if it does not guarantee that the order is immutable. II. data structure of HashMapIn the

The working principle of hashmap is a common Java face test in recent years. Almost every Java programmer knows HashMap, knows where to use HashMap, knows the difference between Hashtable and HashMap, so why is this question so sp