How do I implement a HashMap in Java?

How do I implement a HashMap in Java?

To implement a HashMap in Java, you can use the built-in HashMap class from the java.util package. Here's a simple example:

import java.util.HashMap;

public class Main {
    public static void main(String[] args) {
        HashMap<String, Integer> map = new HashMap<>();
        map.put("One", 1);
        map.put("Two", 2);
        map.put("Three", 3);

        System.out.println(map.get("Two")); // Output: 2
    }
}

What are the key methods of HashMap?

Some key methods of HashMap include:

• put(key, value): Adds a key-value pair to the map.
• get(key): Retrieves the value associated with the specified key.
• remove(key): Removes the key-value pair for the specified key.
• containsKey(key): Checks if the map contains the specified key.
• size(): Returns the number of key-value pairs in the map.

Can you explain how HashMap handles collisions?

HashMap handles collisions using a technique called chaining. When two keys hash to the same index, they are stored in a linked list at that index. This way, multiple key-value pairs can coexist at the same index.

What is the time complexity of HashMap operations?

The average time complexity for put, get, and remove operations in a HashMap is O(1). However, in the worst case (when many collisions occur), it can degrade to O(n).