what is the difference between a map and a hashmap?
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The basic difference is : Map is an interface, i.e. an abstract "thing" that defines how something can be used. HashMap is an implementation of that interface.
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HashMap in Java works on hashing principle. It is a data structure which allows us to store object and retrieve it in constant time O(1) provided we know the key. In hashing, hash functions are used to link key and value in HashMap.
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HashSet is an unordered collection and doesn't maintain any order. ArrayList allows duplicate values in its collection. On other hand duplicate elements are not allowed in Hashset. ... On other hand Hashset allows only one null value in its collection,after which no null value is allowed to be added.
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['You can use ${map["key_name"]} where key_name is the string key i.e. map.put("key_name", value) and you can access the key simply as ${map.key} . – ... ', "i tried doing this one but i throws me an error heres the stacktrace: Property 'bool' not found on type java.util.HashMap$Entry – newbie Sep 12 '13 at 7:01."]
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Dictionary is an abstract class in Java whereas Map is an interface. Since, Java does not support multiple inheritances, if a class extends Dictionary, it cannot extend any other class. Therefore, the Map interface was introduced. Dictionary class is obsolete and use of Map is preferred.
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Map can provide the better searching time in the range of O(log n), whilw list can have the searching time of O(n). std::pair is just for grouping together exactly 2 objects (say, "coordinates on a page" is comprized of X and Y). ... However, you CAN use std::pair as a map value if that's what you want.
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The difference between them is that a List is ordered and a Bag is unordered. So, if you map your to-many association to a java. ... List without specifying the order of your association elements, you're using a Bag and not a List.
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The null key is handled specially in HashMap using 2 separate methods putForNullKey(V value) and getForNullKey(). Null key is mapped always to 0th Index. This null key scenario is treated in isolated methods to eliminate null key code check and improve performance of get and put methods.
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mapValues takes a function B => C , where C is the new type for the values. transform takes a function (A, B) => C , where this C is also the type for the values. So both will result in a Map[A,C] . However with the transform function you can influence the result of the new values by the value of their keys.
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Map is a data structure which helps in storing the data in the form of pairs. The pair consists of a unique key and a value mapped to the key. It helps prevent duplicity. Object follows the same concept as that of map i.e. using key-value pair for storing data.
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Hashtable is a loosely typed (non-generic) collection, this means it stores key-value pairs of any data types. ... Dictionary is a generic collection. So it can store key-value pairs of specific data types.
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A vector stores the data in an internal array that it resizes and you add more elements. An unordered_map uses a hash table internally. ... Nope, indexes in a vector are continuous, in a map they don't have to be. Also, values in a vector are guaranteed to be in continuous memory, not in a map .
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Differences: The difference is set is used to store only keys while map is used to store key value pairs. For example consider in the problem of printing sorted distinct elements, we use set as there is value needed for a key.
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Map- A map cannot contain duplicate keys. Each key can map to at most one value. Collection and Map both are interfaces in java. util package but Collection is used to store objects and Map is used to store the objects for (key,value) based manner.
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5) Nulls: ArrayList can have any number of null elements. HashMap allows one null key and any number of null values.
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HashMap does not allow duplicate keys however it allows to have duplicate values. HashSet permits to have a single null value. HashMap permits single null key and any number of null values.
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Maps and atlases are two things that help us to know information about the location, position or geographical features of a place. ... The key difference between map and atlas is that a map is a representation of an area of land whereas an atlas is a collection of maps. An atlas can contain different types of maps.