Go deep into the ocean of Java Map and explore the fun of data structures

php editor Xinyi leads everyone to delve into the ocean of Java Map and explore the fun of data structures. Map is an interface for storing key-value pairs in Java. It provides a wealth of methods and functions to manage data efficiently. By having an in-depth understanding of the usage and principles of Map, we can make better use of Java's data structures and bring more fun and challenges to programming. Let's explore the world of Java Map together and discover its mysteries and fun!

There are three built-in Map implementations in Java: HashMap, TreeMap and LinkedHashMap. All three implementations offer different features and performance characteristics.

• HashMap is a Map implementation based on hash table. It uses a hash function to map keys to values. The advantage of HashMap is that it is very fast to find and insert data, with an average time complexity of O(1). However, HashMap does not guarantee the order of keys.
• TreeMap is a Map implementation based on red-black trees. It stores keys sequentially in a red-black tree. The advantage of TreeMap is that it guarantees the order of keys, and the speed of finding and inserting data is also very fast, with an average time complexity of O(log n).
• LinkedHashMap is a Map implementation based on linked list. It stores key-value pairs in a linked list. The advantage of LinkedHashMap is that it preserves the insertion order of key-value pairs.

The following is an example of using HashMap:

Map<String, Integer> map = new HashMap<>();
map.put("John", 25);
map.put("Mary", 30);
map.put("Bob", 35);

System.out.println(map.get("John")); // 25
System.out.println(map.get("Mary")); // 30
System.out.println(map.get("Bob")); // 35

This example creates a HashMap and adds three key-value pairs to it. Then, it retrieves the value from the HashMap using the get() method.

Map is a very important data structure that can be used to solve a variety of problems. If you need to store and retrieve data, Map is a great choice.

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