java using hashmap

certainly! in java, a `hashmap` is part of the java collections framework and is used to store key-value pairs. it allows fast retrieval of values based on their associated keys. this tutorial will cover the basics of using a `hashmap`, including how to create one, add items, retrieve values, and iterate over the entries.

### what is a hashmap?

### key features of hashmap

1. **fast access**: average time complexity for get and put operations is o(1).
2. **non-synchronized**: it is not thread-safe; use `concurrenthashmap` if you need thread safety.
3. **order of elements**: it does not maintain any order of its elements (use `linkedhashmap` if order is important).
4. **allows null values**: can have one null key and multiple null values.

### basic operations with hashmap

1. **creating a hashmap**
2. **adding elements**
3. **retrieving elements**
4. **removing elements**
5. **iterating over hashmap**
6. **checking for existence**

### code example

here’s a complete example to illustrate these operations.

### explanation of the code

1. **creating a hashmap**: we create a `hashmap` that maps `string` keys to `integer` values.

2. **adding elements**: we use the `put()` method to add key-value pairs.

3. **retrieving elements**: we use the `get()` method to fetch the value associated with a specific key.

4. **removing an element**: the `remove()` method is used to delete a key-value pair from the map.

6. **checking for existence**: the `containskey()` method checks if a specific key exists in the map.

7. **size of hashmap**: the `size()` method returns the number of key-value pairs in the map.

### conclusion

the `hashma ...

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