How to add key and value to hashmap in Java?

**To add a key and value to a hashmap in Java, you simply use the `put` method.**

HashMap map = new HashMap<>();
map.put(“key”, “value”);

Adding key and value pairs to a hashmap is a fundamental operation in Java programming, especially when dealing with data structures and collections. HashMaps in Java are widely used for storing key-value pairs and providing efficient retrieval and manipulation of data.

Here are some frequently asked questions related to adding key and value to a hashmap in Java:

1. Can a hashmap contain duplicate keys?

No, a hashmap in Java cannot contain duplicate keys. If you try to add a duplicate key, the existing value associated with that key will be replaced by the new value.

2. What happens if I try to add a null key to a hashmap?

In Java, a hashmap can contain one null key. If you try to add another null key, it will overwrite the existing null key.

3. Can a hashmap contain duplicate values?

Yes, a hashmap in Java can contain duplicate values. Each key in the hashmap is unique, but multiple keys can have the same value.

4. How do you check if a key exists in a hashmap?

You can use the `containsKey` method to check if a key exists in a hashmap. It returns true if the key is present in the hashmap, otherwise false.

5. Is it possible to add multiple key-value pairs to a hashmap at once?

No, you have to add key-value pairs one by one in a hashmap in Java using the `put` method.

6. How can you retrieve a value from a hashmap in Java?

You can use the `get` method to retrieve the value associated with a specific key in a hashmap. It returns null if the key is not present in the hashmap.

7. Is the order of key-value pairs maintained in a hashmap?

No, the order of key-value pairs is not guaranteed in a hashmap in Java. If you need to maintain order, you can use a `LinkedHashMap`.

8. Can you iterate over a hashmap in Java?

Yes, you can iterate over a hashmap using different methods like `keySet()`, `values()`, or `entrySet()`.

9. How do you remove a key-value pair from a hashmap?

You can use the `remove` method to remove a key-value pair from a hashmap in Java. It returns the value associated with the key that was removed.

10. Can a hashmap have different types of keys and values?

Yes, a hashmap in Java can have keys and values of different types. However, it is recommended to use the same type for keys and values for clarity and consistency.

11. How do you get the number of key-value pairs in a hashmap?

You can use the `size()` method to get the number of key-value pairs in a hashmap. It returns the size of the hashmap as an integer.

12. What is the default capacity and load factor of a hashmap in Java?

The default initial capacity of a hashmap in Java is 16, and the default load factor is 0.75. The load factor determines when the hashmap should resize itself to accommodate more key-value pairs.

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