Java HashMap containsKey Method

Java HashMap containsKey() method is used to check a key exits or not in HashMap. HashMap.containsKey() Method returns true if this java map contains a mapping for the given key. More formally, returns true if and only if this java map contains a mapping for a key k such that (key==null ? k==null : key.equals(k)). (There can be at most one such mapping.)

Syntax Of HashMap containsKey() Method

This is syntax of map.containskey() method in java

public boolean containsKey(Object key) {

}

Parameters – key key whose presence in this map is to be tested
Return Value – true if this map contains a mapping for the given key
Exception – Its throws following exception
ClassCastException – if the key is of an inappropriate type for this map (optional)
NullPointerException – if the specified key is null and this map does not permit null keys (optional)

Example 1 : Java Hashmap containsKey() method -Value present

In this example we will create java HashMap with String and Integer mapping . We will add values in HashMap using put() method. We check the key “vogue” and “welcomes” are present or not using map containskey() method .Because java map contains these keys , it will returns true .

import java.util.HashMap;
import java.util.Map;

public class HashMapContainsKey {
    public static void main(String[] args) {
		
    	Map<String,Integer> hm = new HashMap<String,Integer>();

		hm.put("java",1);
		hm.put("vogue",2);
		hm.put("welcomes",3);
		hm.put("you",4);

	System.out.println("is key 'vogue' present  = "+hm.containsKey("vogue"));
	System.out.println("is key 'welcomes' present = "+hm.containsKey("welcomes"));
		
	}
}

Output:

is key 'vogue' present  = true
is key 'welcomes' present = true

Example 2 : Java Hashmap containsKey() method -Value not present

We will create java HashMap with String and Integer mapping . We will add values in HashMap using put() method. We check the key “tutorial” and “hashmap” are present or not using HashMap containskey() method . Here ,  java map does not contain these keys , it will returns false .

import java.util.HashMap;
import java.util.Map;

public class HashMapContainsKey1 {
	 public static void main(String[] args) {
			
	    	Map<String,Integer> hm = new HashMap<String,Integer>();

			hm.put("java",1);
			hm.put("vogue",2);
			hm.put("welcomes",3);
			hm.put("you",4);

	System.out.println("is key 'tutorial' present  = "+hm.containsKey("tutorial"));
	System.out.println("is key 'hashmap' present = "+hm.containsKey("hashmap"));
			
		}
}

Output:

is key 'tutorial' present  = false
is key 'hashmap' present = false

Example 3 : Hashmap containsKey() method – Mapping String to Integer keys

In this example we will create HashMap with Integer and String mapping . We add element in map using put method . We will check java map contains keys using map.containskey() method in java. Here , we check key 1 and “2” is present or not in HashMap . We use hashmap.containsKey() Method for key 1 it will returns true and for key “2” it will returns false , because key “2” is a string not a integer .

import java.util.HashMap;
import java.util.Map;

public class HashMapContainsKey2 {
	 public static void main(String[] args) {
			
			Map<Integer,String> hm = new HashMap<Integer,String>();

			hm.put(1,"java");
			hm.put(2, "vogue");
			hm.put(3,"welcomes");
			hm.put(4,"you");

			System.out.println("is key '1' present  = "+hm.containsKey(1));
			System.out.println("is key '2' present = "+hm.containsKey("2"));
			
		}
}

OutPut:

is key '1' present  = true
is key '2' present = false

In this tutorial, We have learned java hashmap containskey() method . By using map.containskey() we can check java map contains specific key or not. It is very useful when we have to check if a key exists in hashmap java or not . You can see more java HashMap program for practice .

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