What are ways to create a HashTable in Java?

In this shot, we will discuss the different ways to create a HashTable in Java.

The HashTable class implements a hashtable, which maps keys to values. A Hashtable is an array of a list.

A Hashtable contains values based on the key.
Hashtable contains unique elements.
Hashtable doesn’t allow null keys or values.
The initial default capacity of Hashtable is 11, whereas the loadFactor is 0.75.

Constructors

The four constructors of the HashTable class are listed below:

HashTable()

This constructs a new, empty hashtable with a default load factor of 0.75 and initial capacity of 11.

HashTable(int capacity)

This constructs a new, empty hashtable with the defined initial capacity and default load factor of 0.75.

HashTable(int capacity, float loadFactor)

This constructs a new, empty hashtable with the defined initial capacity and load factor.

HashTable(Map<? extends K,? extends V> m)

This constructs a new hashtable with the same mappings as the defined in the HashMap.

Code

Let’s look at the code snippet.

import java.util.*;
class Main
{
public static void main(String[] args) 
{
    Hashtable<Integer, String> h1 = new Hashtable<Integer, String>();
    h1.put(1, "Let's");
    h1.put(5, "see");
    h1.put(2, "Hashtable");
    h1.put(9, "in java.");
    System.out.println("The Hashtable h1 is: "+h1);
    Hashtable<Integer, String> h2 = new Hashtable<Integer, String>(3);
    h2.put(1, "Let's");
    h2.put(55, "see");
    h2.put(20, "Hashtable");
    System.out.println("The Hashtable h2 is: "+h2);
    Hashtable<Integer, String> h3 = new Hashtable<Integer, String>(3,0.5f);
    h3.put(11, "Let's");
    h3.put(15, "see");
    h3.put(14, "Hashtable");
    System.out.println("The Hashtable h3 is: "+h3);
    Map<Integer, String> map = new HashMap<>();
    map.put(17, "Let's");
    map.put(62, "see");
    map.put(33, "Hashtable");
    Hashtable<Integer, String> h4 = new Hashtable<Integer, String>(map);
    System.out.println("The Hashtable h4 is: "+h4);
}
}

Explanation

In line 1, we imported the required package.
In line 2, we made a Main class.
In line 4, we made a main function.
In line 6, we constructed a HashTable using the first constructor that created a HashTable with a default initial capacity (11) and load factor (0.75) consisting of Integer type keys and String type values.
In lines 7 to 10, we inserted key-value pairs in the Hashtable by using the Hashtable.put() method.
In line 11, we displayed the HashTable h1.
In line 13, we constructed a HashTable using the second constructor that created a HashTable with a user defined initial capacity, i.e., 3 here, and default load factor (0.75) consisting of Integer type keys and String type values.
In lines 14 to 16, we inserted key-value pairs in the Hashtable by using the Hashtable.put() method.
In line 17, we displayed the HashTable h2.
In line 19, we constructed a HashTable using the third constructor that created a HashTable with a user defined initial capacity, i.e., 3 and load factor, i.e., 0.5 here, consisting of Integer type keys and String type values.
In lines 20 to 22, we inserted key-value pairs in the HashTable by using the Hashtable.put() method.
In line 23, we displayed the HashTable h3.
In line 25, we declared a Hashmap with Integer type keys and String type values.
In lines 26 to 28, we inserted key-value pairs in the HashMap by using the HashMap.put() method.
In line 29, we constructed a HashTable using the fourth constructor that created a HashTable with the mapping of the created HashMap that is being passed.
In line 30, we displayed the HashTable h4.

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