hash table example in java

This is a relatively expensive operation. Please let me know if you liked the Java Hashtable tutorial with examples in the comments section below. There are few more differences between HashMap and Hashtable class, you can read them in detail at: Difference between HashMap and Hashtable. Your email address will not be published. 11) boolean containsKey(Object key): Tests if the specified object is a key in this hashtable. The returned Collection is a view that is backed by the original Hashtable object. Hashtable implements Serializable, Cloneable, Map interfaces and extends Dictionary.The direct subclasses are Properties, UIDefaults.. Constructors: In order to create a Hashtable, we need to import it from java.util.Hashtable.There are various ways in which we can create a Hashtable. *; public class HashTableDemo { public static void main(String args[]) { // … The below given are some of the important methods of the Hashtable class in Java. Any non-null object can be used as a key or as a value. Hashtable hashtable = new Hashtable(); 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. If you want to create a new mapping if the key does not exist, but do not want to replace the value if the key already exists then use the putIfAbsent method. Java Hashtable tutorial with examples will help you understand how to use Java Hashtable in an easy way. In Java version 2, the Hashtable class was rewritten to implement the Map interface and that made it a member of the Java Collection Framework. I tried Hashtable – it allows to put null keys as well as null values ?? The shallow copy means that only key and value object references are copied, not the actual objects. Note that this method is identical in functionality to containsValue, (which is part of the Map interface in the collections framework). To successfully store and retrieve objects from a hashtable, the objects used as keys must implement the hashCode … Returns false if the value isn’t found. 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. The Hashtable class provides several constructors using which we can create new objects of the hashtable. The clone method of the Hashtable class returns a shallow copy of this hashtable object. HashMap, the Hashtable is synchronized. All the structure of the hashtable itself is copied, but the keys and values are not cloned. Sitemap. Java Hashtable Examples. 7) void rehash(): Increases the size of the hash table and rehashes all of its keys. As we can see from the output, the value for key “1” in hashtable was replaced by the value for key “1” in the hashmap object. This operation is more expensive than the containsKey method. hashtable.put(“”, “ram”); The Hashtable class is contained in the java.util package. The Hashtable class is contained in the java.util package. Clears this hashtable so that it contains no keys.. 2) Object clone(): Creates a shallow copy of this hashtable. Over the years I have worked with many fortune 500 companies as an eCommerce Architect. hashtable.put(“S”, “”); Once we get the hashtable values enumeration, we can iterate through it using the hasMoreElements and nextElement methods. Required fields are marked *, Copyright © 2012 – 2020 BeginnersBook . The Hashtable class also provides an overloaded constructor that accepts a map object. The Hashtable containsKey method returns true if the specified key is mapped to any value in the hashtable object. That means that the elements may not be returned in the same order in which they were inserted into the hashtable. If the key is not mapped to the specified old value, or if the key does not exist, it returns false. The Hashtable putIfAbsent method maps a given key with the given value and returns null if the key does not exist. The default Hashtable constructor creates a new and empty hashtable object. The put method returns null if the specified key was not mapped to any value previously. 8) Object remove(Object key): Removes the key (and its corresponding value) from this hashtable. If the Hashtable value is an object of a custom class, then the custom class needs to override the equals and hashCode methods for the contains and containsValue methods to work properly. The Hashtable replace method replaces the value mapped to the given key in the hashtable object.

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