Java HashMap is a data structure that allows you to store key-value pairs. It is useful for mapping one value to another and retrieving values based on a key. In this blog, we will explore Java HashMap in detail, including how to declare and use it, and provide example code snippets to illustrate each concept.
Declaring a Java HashMap:
To declare a Java HashMap, you need to import the java.util.HashMap class and create an instance of it. Here is an example:
import java.util.HashMap; HashMap<String, Integer> map = new HashMap<String, Integer>();
In the above example, we declare a HashMap called map that maps strings to integers.
Adding Elements to a Java HashMap:
To add elements to a Java HashMap, you can use the put() method. Here is an example:
map.put("John", 25);
map.put("Mary", 30);
map.put("Tom", 35);
In the above example, we add three key-value pairs to the map.
Accessing Elements in a Java HashMap:
To access elements in a Java HashMap, you can use the get() method. Here is an example:
int age = map.get("John");
In the above example, we retrieve the value associated with the key “John”.
Removing Elements from a Java HashMap:
To remove elements from a Java HashMap, you can use the remove() method. Here is an example:
map.remove("Mary");
In the above example, we remove the key-value pair associated with the key “Mary”.
Iterating over a Java HashMap:
To iterate over a Java HashMap, you can use a for-each loop. Here is an example:
for (String name : map.keySet()) {
int age = map.get(name);
System.out.println(name + " is " + age + " years old.");
}
In the above example, we iterate over the keys in the map and retrieve the associated values.
HashMap vs HashTable:
HashMap and HashTable are both data structures used to store key-value pairs. HashMap is not synchronized, which makes it faster than HashTable. HashTable is synchronized, which makes it thread-safe.
Conclusion:
Java HashMap is a useful data structure that allows you to store key-value pairs and retrieve values based on a key. In this blog, we explored how to declare and use a Java HashMap, including how to add, access, and remove elements, as well as how to iterate over the map. We also compared HashMap with HashTable. If you need a data structure that is fast and not thread-safe, consider using a Java HashMap.
