How to Convert a HashTable to Other Collections Types in Java?
Last Updated :
12 Feb, 2024
In Java, a Hashtable is a data structure that stores the data in the form of key and value pairs. And each key is mapped to a specific value. It implements the Map interface. HashTable provides a simple way to access the data using the unique keys.
In this article, we will learn how to convert a HashTable to other Collection types in Java.
Note: HashTable does not allow NULL keys or NULL values.
Conversion of HashTable to other Collections:
There are several types of converting the HashTable to other collections, here are some conversions:
- HashTable to ArrayList: It allows the retrieval of keys and values in sequential order.
- HashTable to HashSet: It will remove duplicate values and help us to maintain a unique set of data.
- HashTable to TreeMap: It sorts the entries based on the custom comparator or natural order.
- HashTable to LinkedHashMap: This will preserve the insertion order and maintain the data in the order in which elements were added.
Program to Convert a HashTable to Other Collections Types in Java
Below is the implementation of Convert a HashTable to Other Collections Types:
Java
import java.util.*;
public class ExampleConversion
{
public static void main(String[] args)
{
Hashtable<Integer, String> hashTable = new Hashtable<>();
hashTable.put( 1 , "One" );
hashTable.put( 2 , "Two" );
hashTable.put( 3 , "Three" );
List<Integer> arrayList = new ArrayList<>(hashTable.keySet());
System.out.println( "Converted ArrayList Output: " + arrayList);
Set<String> hashSet = new HashSet<>(hashTable.values());
System.out.println( "Converted HashSet output : " + hashSet);
Map<Integer, String> treeMap = new TreeMap<>(hashTable);
System.out.println( "Converted TreeMap output : " + treeMap);
Map<Integer, String> linkedHashMap = new LinkedHashMap<>(hashTable);
System.out.println( "Converted LinkedHashMap output : " + linkedHashMap);
}
}
|
Output
Converted ArrayList Output: [3, 2, 1]
Converted HashSet output : [One, Two, Three]
Converted TreeMap output : {1=One, 2=Two, 3=Three}
Converted LinkedHashMap output : {3=Three, 2=Two, 1=One}
Explanation of the above Program:
In the above example,
- We have created a Hashtable named
hashTable
and add some key-value pairs to it.
- We have converted the Hashtable to different collection types.
- For ArrayList we have used the
keySet()
method to get a Set of keys from the Hashtable and then create an ArrayList from this set.
- For HashSet we have used the
values()
method to get a Collection of values from the Hashtable and then create a HashSet from this collection.
- For TreeMap we directly create a TreeMap from the Hashtable.
- For LinkedHashMap we directly create a LinkedHashMap from the Hashtable.
- At last, it prints out the converted collection types.
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