How to check whether a particular key is present in HashMap ?

In this article, we will discuss how to check whether a key is present in the invoking HashMap or Not

1. Searching a key from HashMap :

  • Method signature : boolean containsKey(Object key)
  • This method is used to search specified key from invoking Map object;
  • it can be HashMap or LinkedHashMap or TreeMap
  • Returns true, if key is present;
  • otherwise return false
  • Note: Same example can be used to search for any particular key in LinkedHashMap and TreeMap

SearchSpecifiedKeyFromHashMap.java

package in.bench.resources.java.map;

import java.util.HashMap;

public class SearchSpecifiedKeyFromHashMap {

	public static void main(String[] args) {

		// creating HashMap object of type <String, String>
		HashMap<String, String> hashMap = new HashMap<String, String>();


		// adding key-value pairs to HashMap object
		hashMap.put("Google", "Sundar Pichai");
		hashMap.put("Facebook", "Mark Zuckerberg");
		hashMap.put("LinkedIn", "Reid Hoffman");
		hashMap.put("Apple", "Steve Jobs");
		hashMap.put("Microsoft", "Bill Gates");


		// printing all Key-Value pairs
		System.out.println("all Key-Value pairs:\n\n" 
				+ hashMap);


		// search for key
		boolean searchKey = hashMap.containsKey("Apple");


		// print to console - searchKey value
		System.out.println("\n\nWhether key 'Apple' is present in hashMap ? " 
				+ searchKey);


		// print to console
		System.out.println("\n\nWhether key 'Facebook' is present in hashMap ? "
				+ hashMap.containsKey("Facebook"));


		// print to console
		System.out.println("\n\nWhether key 'Whatsup' is present in hashMap ? "
				+ hashMap.containsKey("Whatsup"));
	}
}

Output:

all Key-Value pairs:

{Google=Sundar Pichai, LinkedIn=Reid Hoffman, Apple=Steve Jobs, 
Microsoft=Bill Gates, Facebook=Mark Zuckerberg}


Whether key 'Apple' is present in hashMap ? true


Whether key 'Facebook' is present in hashMap ? true


Whether key 'Whatsup' is present in hashMap ? false

References:

Happy Coding !!
Happy Learning !!

How to check whether a particular value is present in HashMap ?
How to delete all entries of HashMap