Java HashMap.isEmpty()

In this tutorial, we will learn about the Java HashMap.isEmpty() function, and learn how to use this function to check if this HashMap is empty or not, with the help of examples.

isEmpty()

HashMap.isEmpty() returns true if this map contains no key-value mappings, or false if this map contains one or more key-value mappings.

The syntax of isEmpty() function is 

isEmpty()

Returns

The function returns boolean value.

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Examples

1. HashMap isEmpty() for an empty HashMap

In this example, we will initialize a HashMap hashMap with no mappings in it. To check if this hashMap is emtpy, call isEmpty() method on this HashMap. Since the haspMap is empty, isEmpty() should return true.

Java Program

import java.util.HashMap;

public class Example{ 
	public static void main(String[] args) {
		HashMap<Integer, String> hashMap = new HashMap<>();
		
		boolean result = hashMap.isEmpty();
		System.out.println("Is the HashMap empty? " + result);
	}
}

Output

Is the HashMap empty? true

2. HashMap isEmpty() for an non-empty HashMap

In this example, we will initialize a HashMap hashMap with four mappings in it. To check if this hashMap is emtpy, call isEmpty() method on this HashMap. Since the haspMap is not empty, isEmpty() should return false.

Java Program

import java.util.HashMap;

public class Example{ 
	public static void main(String[] args) {
		HashMap<Integer, String> hashMap = new HashMap<>();
		hashMap.put(1, "A");
		hashMap.put(2, "B");
		hashMap.put(3, "C");
		hashMap.put(4, "D");
		
		boolean result = hashMap.isEmpty();
		System.out.println("Is the HashMap empty? " + result);
	}
}

Output

Is the HashMap empty? false

3. isEmpty() – When HashMap is null

In this example, we will initialize a HashMap hashMap with null value. To check if this hashMap is emtpy, call isEmpty() method on this HashMap. Since the haspMap is null, isEmpty() should throw java.lang.NullPointerException.

Java Program

import java.util.HashMap;

public class Example{ 
	public static void main(String[] args) {
		HashMap<Integer, String> hashMap = null;
		
		boolean result = hashMap.isEmpty();
		System.out.println("Is the HashMap empty? " + result);
	}
}

Output

Exception in thread "main" java.lang.NullPointerException
	at Example.main(Example.java:7)

Conclusion

In this Java Tutorial, we have learnt the syntax of Java HashMap.isEmpty() function, and also learnt how to use this function with the help of examples.