A linked list is made up of a sequence of connected (linked) nodes. A hashtable is usually backed by an array, and is an association of keys and values. When an object is added to the array it becomes a value; the object is hashed to get a key (an index into the array).
While these two data structures are nearly identical in Java, there are a few distinguishing features. The main two are that a HashMap is not synchronized (Hashtable is thread-safe) and that HashMap allows keys and values to be null (Hashtable will throw an Exception if you attempt to add a null key or value).
See the related link below for the Java API documentation for the Hashtable class and its methods.
Dictionary, Hashtable ,Properties ,Stack and vector are the legacy classes in java
Inner classes are very useful for classes that are written specifically to be used with the encompassing class. A good example of this would be a LinkedListNode class being part of a LinkedList class: public class LinkedList { private LinkedListNode root; private class LinkedListNode { private Object data; private LinkedListNode nextNode; } } No class except your LinkedList class needs to know anything about the LinkedListNode class. So we hide it so no one else needs to worry about what it does.
No. While there are quite a few which use arrays to store their data (ArrayList, HashMap, Vector, etc.) the typical counter example is a LinkedList. Java's implementation of the LinkedList class uses the standard Entry-Entry.next method of connecting elements in the list. You can even consider a collection as something that is similar to an array but with enhanced features. Collections have a lot of features that arrays do not have.
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1) hashtable is synchronized , hashmap is not 2) hashtable is slow , hashmap is fast 3) hashtable is old and hashmap is new
HashTableLike Vector, Hashtable has existed from prehistoric Java times. For fun, don't forget to note the naming inconsistency: HashMap vs. Hashtable. Where's the capitalization of t? Oh well, you won't be expected to spell it. Anyway, just as Vector is a synchronized counterpart to the sleeker, more modern ArrayList, Hashtable is the synchronized counterpart to HashMap. Remember that you don't synchronize a class, so when we say that Vector and Hashtable are synchronized, we just mean that the key methods of the class are synchronized. Another difference, though, is that while HashMap lets you have null values as well as one null key, a Hashtable doesn't let you have anything that's null.
Dictionary is typed (sо valuetypes dоn't need bоxing), a Hashtable isn't (sо valuetypes need bоxing). Hashtable has a nicer way оf оbtaining a value than dictionary IMHО, because it always knоws the value is an оbject. Thоugh if yоu're using .NET 3.5, it's easy tо write an extensiоn methоd fоr dictionary tо get similar behaviоr.The Hashtable class is a specific type оf dictionary class that uses an integer value (called a hash) tо aid in the stоrage оf its keys. The Hashtable class uses the hash tо speed up the searching fоr a specific key in the cоllectiоn. Every оbject in .NET derives frоm the Оbject class. This class suppоrts the GetHash methоd, which returns an integer that uniquely identifies the оbject. The Hashtable class is a very efficient cоllectiоn in general. The оnly issue with the Hashtable class is that it requires a bit оf оverhead, and fоr small cоllectiоns (fewer than ten elements) the оverhead can impede perfоrmance.There is оne mоre impоrtant difference between a HashTable and Dictionary. If yоu use indexers tо get a value оut оf a HashTable, the HashTable will successfully return null fоr a nоn-existent item, whereas the Dictionary will thrоw an errоr if yоu try accessing a item using a indexer which dоes nоt exist in the Dictionary.The HashTable is the base class that is weakly typed; the DictionaryBase abstract class is strоnly typed and uses internally a HashTable.A strange thing noticed abоut Dictionary is, when we add the multiple entries in Dictionary, the оrder in which the entries are added is maintained. Thus if you apply a fоreach оn the Dictionary, you will get the recоrds in the same оrder you have inserted them. Whereas, this is nоt true with nоrmal HashTable, when you add same recоrds in Hashtable the оrder is nоt maintained. If 'Dictionary is based оn Hashtable' is true, why Dictionary maintains the оrder but HashTable dоes nоt?As tо why they behave differently, it's because Generic Dictionary implements a hashtable, but is nоt based оn System.Cоllectiоns.Hashtable. The Generic Dictionary implementatiоn is based оn allоcating key-value-pairs frоm a list. These are then indexed with the hashtable buckets fоr randоm access, but when it returns an enumeratоr, it just walks the list in sequential оrder - which will be the оrder оf insertiоn as lоng as entries are nоt re-used.
A pointer is a memory reference to a data structure. So when you allocate memory for your list elements, they will be stored at some address X in your system memory. A pointer is simply a variable that contains that address X. You can access the memory that a pointer points to by dereferrencing it with the * operator.Ex:int main(){LinkedList *x; /* Declare a pointer to a linked list (a type which you would have to define using "struct" or "class") */x = new LinkedList(); /* Here we create (aka "instantiate") a LinkedList object and allocate memory for it, x now contains (points to) the memory address of our LinkedList object */// You can now access any LinkedList members through x, for example x->next might point you to the next element of your LinkedList
Assuming you're using the Hashtable.toString() method, output order depends on the order of the backend storage. The array of Entry objects (the "table" array) seems to actually be read backwards by the Hashtable iterator. The order of elements in the table array, of course, depends on how the hash function for the keys of the Hashtable works.
ArrayListLinkedList1. ArrayList uses a dynamic array.1..Linked List uses doubly linked list.2. ArrayList is not efficient for manipulation because a lot of shifting is required.2.. LinkedList is efficient for manipulation
Dictionary, Hashtable ,Properties ,Stack and vector are the legacy classes in java
See the related link below for the Java API documentation for the Hashtable class and its methods.
A primitive data structure is generally a basic structure that is usually built into the language, such as an integer, an array or a linked-list.A non-primitive data structure is built out of primitive data structures linked together in meaningful ways, such as a binary search tree, AVL Tree, Hashtable, etc.
HashMapThe HashMap gives you an unsorted, unordered Map. When you need a Map and you don't care about the order (when you iterate through it), then HashMap is the way to go; the other maps add a little more overhead. Where the keys land in the Map is based on the key's hashcode, so, like HashSet, the more efficient your hashCode() implementation, the better access performance you'll get. HashMap allows one null key and multiple null values in a collection.HashTableLike Vector, Hashtable has existed from prehistoric Java times. For fun, don't forget to note the naming inconsistency: HashMap vs. Hashtable. Where's the capitalization of t? Oh well, you won't be expected to spell it. Anyway, just as Vector is a synchronized counterpart to the sleeker, more modern ArrayList, Hashtable is the synchronized counterpart to HashMap. Remember that you don't synchronize a class, so when we say that Vector and Hashtable are synchronized, we just mean that the key methods of the class are synchronized. Another difference, though, is that while HashMap lets you have null values as well as one null key, a Hashtable doesn't let you have anything that's null.
public class ArrayList public class LinkedList extends AbstractList extends AbstractSequentialList implements List, RandomAccess, Cloneable, Serializableimplements List, Cloneable, Serializable Resizable-array implementation of the List interface.Linked list implementation of the List interface Implements all optional list operations, and permits all elements, including null. Implements all optional list operations, and permits all elements (including null).
Inner classes are very useful for classes that are written specifically to be used with the encompassing class. A good example of this would be a LinkedListNode class being part of a LinkedList class: public class LinkedList { private LinkedListNode root; private class LinkedListNode { private Object data; private LinkedListNode nextNode; } } No class except your LinkedList class needs to know anything about the LinkedListNode class. So we hide it so no one else needs to worry about what it does.