How to check if a key exists in a HashMap in Java

Given a HashMap and a key in Java, the task is to check if this key exists in the HashMap or not. Examples:

Input: HashMap: {1=Geeks, 2=ForGeeks, 3=GeeksForGeeks}, key = 2
Output: true

Input: HashMap: {1=G, 2=e, 3=e, 4=k, 5=s}, key = 10
Output: false

1. Using Iterator (Not Efficient):
   1. Get the HashMap and the Key
   2. Create an iterator to iterate over the HashMap using HashMap.iterate() method.
   3. Iterate over the HashMap using the Iterator.hasNext() method.
   4. While iterating, check for the key at that iteration to be equal to the key specified. The entry key of the Map can be obtained with the help of entry.getKey() method.
   5. If the key matches, set the flag as true.
   6. The flag value after iterating, contains the result.
   Below is the implementation of the above approach: Program 1:
   Output:

   HashMap: {1=Geeks, 2=ForGeeks, 3=GeeksForGeeks}
   Does key 2 exists: true
   

   Program 2: To show why this method is not suggested. If the HashMap contains null values, then this method will throw NullPointerException. This makes this method a non suggestable method to use.
   Output:

   HashMap: {null=GeeksForGeeks, 1=Geeks, 2=ForGeeks}
   java.lang.NullPointerException
   

2. Using HashMap.containsKey method(Efficient):
   1. Get the HashMap and the Key
   2. Check if the key exists in the HashMap or not using HashMap.containsKey() method. If the key exists, set the flag as true.
   3. The flag value, contains the result.
   Below is the implementation of the above approach: Program 1: