A HashMap in Java is a class that allows you to store key-value pairs, where keys should be unique. It is a part of Javas collection since Java 1.2 and is found in the java.util package. HashMaps use a hash function to map keys to indices in an array, which allows for a quick lookup of values based on keys.
Some key features of HashMap in Java include:
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Keys: Keys are unique identifiers used to associate each value on a map. A key can be any object.
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Values: Values are stored in key-value pairs. One key or multiple values could be null in the entire HashMap.
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Capacity: The initial capacity of a HashMap is 16, and it increases as more elements are added to it. When the number of elements exceeds the load factor (default 0.75), the capacity is doubled.
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Methods: HashMap class has many useful methods, such as put(), get(), remove(), size(), and clear() .
To create a HashMap in Java, you must first import the java.util.HashMap package. Here is an example of how to create a HashMap:
HashMap<K, V> numbers = new HashMap<>();
In the above code, K represents the key type, and V represents the type of values. To add elements to the HashMap, you can use the put() method. To access a value, you can use the get() method and refer to its key. To remove an item, you can use the remove() method and refer to the key.
Overall, HashMaps are useful for storing and retrieving data quickly based on keys.
