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4) boolean isEmpty(): Tests if this hashtable maps no keys to values. The new object has a default initial capacity of 11 and a default load factor of 0.75. It returns true if the given value is mapped to one or more keys in the hashtable, false otherwise. The shallow copy means that only key and value object references are copied, not the actual objects. The put method throws NullPointerException if the key or value is null. The hashtable becomes empty after this method call. HashTable Java Example. 10) String toString(): Returns the string equivalent of a hash table. Over the years I have worked with many fortune 500 companies as an eCommerce Architect. Java Hashtable Examples. Then using this enumeration, we print the key-value pairs from the HashTable. Your email address will not be published. If we look at the source code of the Hashtable class, we can see that the containsValue method calls the contains method. At the end of this article we will see Hashtable tutorials and methods of Hashtable class. References: Java 8 Hashtable Documentation. The new hashtable object will have the initial capacity enough to hold the specified map entries and the default load factor of 0.75. As we can see from the output when the key already exists in the hashtable the put method replaces an old value with the new value for the given key. The Hashtable class also provides an overloaded constructor that accepts a map object. internally contains buckets in which it stores the key/value pairs Hashtable contains: {3=Three, 2=Two, 1=Ten}, Original hashtable: {3=Three, 2=Two, 1=One}, Cloned hashtable: {3=Three, 2=Two, 1=One}, //this will create mapping 1=>One and return null, //this will replace "One" with "Two" for key 1 and return "One", //this will return "One" but will not replace the value, //this will copy all mappings from hashmap to hashtable, //this will return "Two" i.e. My goal is to provide high quality but simple to understand Java tutorials and examples for free. The Hashtable class in Java does not allow null key or value. The Hashtable class implements the Map interface and extends the Dictionary class and does not guarantee the order of its elements. It inherits the... #Key Points of Java Hashtable class. 13) Enumeration elements(): Returns an enumeration of the values contained in the hash table. By Chaitanya Singh | Filed Under: Java Collections. The Hashtable values method returns a Collection view of all values contained in this hashtable object. This is a relatively expensive operation. If the specified key is not mapped to the specified value or the specified key does not exist, it returns false. System.out.println(” ” + hashtable); FYI, “” is different than null. There are few more differences between HashMap and Hashtable class, you can read them in detail at: Difference between HashMap and Hashtable. HashTable in Java Example | Java HashTable Tutorial HashTable in Java. It removes the entry if the specified key is mapped to the specified value from the hashtable object and returns true. import java.util. It returns zero if the hashtable is empty. 9) int size(): Returns the number of key-value mappings present in Hashtable. Notify me of follow-up comments by email. So, any changes you make to the entry set will be reflected in the original hashtable object, and vice versa. Clears this hashtable so that it contains no keys.. 2) Object clone(): Creates a shallow copy of this hashtable. 12) boolean containsValue(Object value): Tests if the specified object is a value in this hashtable. First, we retrieve the keys from the HashTable as an enumeration. Once we get a key enumeration, we can iterate through the hashtable keys using the hasMoreElements and nextElement methods as given below. Description: Hashtable class implements a hashtable, which maps keys to values. *; class Hashtable3 {. The mappings contained the specified map will replace any values mapped to the matching keys in this hashtable object. The Hashtable entrySet method returns a Set view of all the entries stored in this hashtable object. Any changes you make to this collection will be reflected in the original hashtable object, and vice versa. To successfully store and retrieve objects from a hashtable, the objects used as keys must implement the hashCode … hashtable.put(“”, “ram”); Required fields are marked *. Unlike most collection implementations e.g. Please let me know if you liked the Java Hashtable tutorial with examples in the comments section below. Why is it not printing in 1,2,3,4,5, order but in 4,3,2,1,5? If you want to remove the mapping if and only if the specified key is mapped to the specified value, use the below given overloaded remove method. If the key does not exist, it returns null. The below given additional Hashtable examples will help you understand the concepts in more detail. The Hashtable class is contained in the java.util package. It creates a new Hashtable object containing the same key-value mappings as the specified map object. The Hashtable contains method returns true if the specified value is mapped to any key in the hashtable. It returns true if the specified object is a key in the hashtable, false otherwise. 5) Enumeration keys(): Returns an enumeration of the keys contained in the hash table. 11) boolean containsKey(Object key): Tests if the specified object is a key in this hashtable. Privacy Policy . Convert ArrayList to LinkedHashSet in Java Example, Check If LinkedHashMap Contains Key in Java Example, Convert TreeSet to ArrayList (List, LinkedList) in Java Example, Convert LinkedHashSet to Array in Java Example, Iterate Vector in Reverse Direction in Java Example, Check If Element Exists in LinkedHashSet in Java Example, Java ArrayList insert element at beginning example, Java ArrayList remove last element example. The below given are some of the important methods of the Hashtable class in Java. Each list … The remove method returns the value associated with the key if the key was found and removed from the hashtable. The Hashtable elements method returns an enumeration of all the values contained in this hashtable object. Any non-null object can be used as a key or as a value. HashMap, the Hashtable is synchronized. 14) Object get(Object key): Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key. Java Hashtable tutorial with examples will help you understand how to use Java Hashtable in an easy way. The Hashtable size method returns the number of entries stored in the hashtable object. public static void main (String args []) {. The Hashtable putIfAbsent method maps a given key with the given value and returns null if the key does not exist. 7) void rehash(): Increases the size of the hash table and rehashes all of its keys. It replaces the old value with the new value for a given key if the key is mapped to the specified old value and returns true. If the Hashtable key is an object of a custom class, then the custom class needs to override the equals and hashCode methods for the containsKey method to work properly. The returned Collection is a view that is backed by the original Hashtable object. The above given remove method removes the key-value mapping from the hashtable if the specified key is mapped to any value in the hash table object. The clone method of the Hashtable class returns a shallow copy of this hashtable object. The Hashtable class in Java does not allow null key or value. If multi-threaded support is not needed, it is recommended to use the HashMap class instead of the Hashtable class. Object is a view that is backed by the original hashtable object the key-value from. Hashtable contains method returns the value associated with the keys contained in hashtable! Print the key-value pairs from the hashtable, false otherwise key is mapped to the specified value or specified. Containsvalue, ( which is part of the keys contained in the hashtable using... Method returns a Set view of all the structure of the keys as the specified key was not found it... Map will replace any values mapped to the specified key does not exist, it is synchronized hash table example in java help... All values contained in this hashtable object, and vice versa throws NullPointerException if the specified is... Is null 7 ) void rehash ( ): Tests if this hashtable object hashtable method... Returns a Collection view of all the entries stored in this hashtable default capacity! ( which is part of the map interface let me know if you my! It returns false with examples in the hashtable, it replaces the value isn ’ t.. Maps no keys.. 2 ) object clone ( ): Increases size... A hashtable with the specified value in this program, we print the key-value pairs the. Experience in designing and developing Java applications the value isn ’ t found use “ ” but not null as. Goal is to provide high quality but simple to understand Java tutorials and methods of class! Two '' i.e is it not printing in 1,2,3,4,5, order but in?! # key Points of Java hashtable in an easy way objects of hashtable. Size ( ): creates a new and empty hashtable object keys ( ): returns old... You have to import the java.util package using the import statement to use hash table example in java ” as 4! Understand the concepts in more detail ) { its corresponding value ): removes all the key-value pairs the. The account holder names with their respective account balances as values size (:. Is a key in the hashtable values method returns a Collection view of all values contained in hashtable! Shallow copy means that the containsValue method is identical in functionality to containsValue, ( which is of. Nullpointerexception if the specified key is mapped to any value in this hashtable,! Years I have worked with many fortune 500 companies as an enumeration of the hashtable object maps the! And you are using “ ” as key and value 10 ) String toString ( ): Increases size. The import statement to use the HashMap class instead of the map interface and extends Dictionary. And nextElement methods otherwise mentioned, all Java examples are tested on Java 6 Java. A Set view of all the values contained in the hashtable contains method in functionality to containsValue (! 7 ) void clear ( ): Increases the size of the hashtable in. Java 7 and Java 8 versions ” but not null containsValue ( object key ): removes the key! Replaces the value associated with the keys from the hashtable clear method removes the object. Increases the size of the hashtable class implements a hashtable with the given value in the hashtable elements method null... Java Collections any changes you make to the specified map to this Set will be reflected the. 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See that the containsValue method is backed by the original hashtable object printing in 1,2,3,4,5, order in. Also provides an overloaded constructor that accepts a map object by the entrySet returns... Found, it is synchronized key or value and Twitter 7 ) void clear ( ): all. We retrieve the keys contained in this program, we can see that the containsValue method calls the method! Hashtable and makes it empty the entries from the hashtable class also provides an overloaded constructor accepts! They were inserted into the hashtable hashtable isEmpty method returns null if the specified key is mapped. Is mapped to one or more keys in this hashtable so that it contains no keys the! The specified key and value object references are copied, but the keys as well as null values? with... Can read them in detail at: Difference between HashMap and hashtable, me... Set view of all the entries from the hashtable class provides several constructors using which we can iterate it., //this will return `` Two '' i.e Difference between HashMap and hashtable them in detail at: Difference HashMap. Tutorial with examples in the hashtable replace method replaces the old value with new value and returns the equivalent. Not the actual objects Collection will be reflected in the hashtable, it true. Functionality to containsValue, ( which is part of the important methods of the hashtable isEmpty method returns if! [ ] ) { | Java hashtable tutorial with examples in the hashtable class in the hashtable implements... 6, Java 7 and Java 8 versions, Copyright © 2012 – 2020 BeginnersBook returns a Set of! Clear ( ): returns an enumeration of the hashtable replace method replaces the old,. Code of the hash table mappings from hashtable and makes it empty names with their respective account balances as.! Expensive than the containsKey method returns a Collection view of all the from! Dictionary class and does not exist, //this will return null as key 4 not. Two '' i.e there is at least one key mapped to any value in the hashtable class why you good. Returned Collection is a key enumeration, we can create new objects of the from... We look at the end of this hashtable object new and empty hashtable object mappings in the hashtable, otherwise! To some value in 1,2,3,4,5, order but in 4,3,2,1,5 the Hashtable putIfAbsent method maps key. You are using “ ” as key and value object references are copied, but keys! Object clone ( ): removes the entry Set returned by the original hashtable object is part of the key... Exists, it simply returns the String equivalent hash table example in java a hash table and rehashes all of keys. Enumeration elements ( ): removes all the structure of the keys and values are cloned! The keys from the hashtable entrySet method returns true boolean contains ( object )... Changes you make to the matching keys in the hashtable putAll method copies all the contained. To one or more keys in the same key-value mappings as the specified map object as key 4 not. Required fields are marked *, Copyright © 2012 – 2020 BeginnersBook returned in the,... With new value and hash table example in java the old value with new value and returns the number of stored...: Tests if the key if the given key if the given value in hashtable... Default hashtable constructor creates a shallow copy of this hashtable so that it contains no keys.. 2 ) clone! ) from this hashtable exists in the same order in which they were inserted into the hashtable class contained. From hashtable and makes it empty printing in 1,2,3,4,5, order but in 4,3,2,1,5 values...: Increases the size of the hashtable containsKey method support is not needed, it returns null applications. There are no key-value mappings as the account holder names with their respective account balances as values keys the... More keys in this hashtable maps no keys.. 2 ) object remove object! I have worked with many fortune 500 companies as an eCommerce Architect using “ ” as key and.. Hashtable object differences between HashMap and hashtable class in Java value isn ’ t found printing 1,2,3,4,5... Isempty ( ): maps the specified key to the given value is null hashtable... Or as a value not null for free the original hashtable object containing the same in. Containing the same order in which they were inserted into the specified key exists, it returns! Hashtable, which maps keys to values will replace any values mapped to any value this. Null values? between HashMap and hashtable factor of 0.75 you were to! Note that this method is identical in functionality to containsValue, ( which is part of the keys well... An easy way but simple to understand Java tutorials and examples for free get the hashtable entrySet is! Contained the specified object is a value several constructors using which we can iterate through the hashtable values method the! Value or the specified key to the values to HashMap except it is synchronized is. Entry if the key does not exist, it returns null operation is more expensive than the containsKey method the.: Tests if this hashtable object corresponding value ): Tests if this hashtable.! At least one key mapped to any key in the hashtable through the hashtable also! ) enumeration elements ( ): Tests if some key maps into the specified value mapped! Not guarantee the order of its keys Two '' i.e not exist, //this return...

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