What does key mean in java

Key in Java is a data structure stored in a collection, used to identify the storage location of a specific value in the collection. Uses for these keys include finding, retrieving, updating, and removing values ​​from the collection. They implement the equality and hash code methods in the Key interface and are often overridden by the actual type implementation (e.g., String, Integer) to provide type-specific comparison and hashing functionality.

Key in Java

In Java, Key is stored in a collection (such as HashMap, TreeMap) A part of a data structure that uniquely identifies where a specific value in a collection is stored.

Purpose:

• Find and retrieve values ​​in a collection.
• Remove values ​​from the collection.
• Update the values ​​in the collection.

Implementation:

The Key interface in Java defines basic methods, including:

• equals(): Compare two Keys for equality.
• hashCode(): Returns the hash code of Key.

Typically, the actual Key implementation (e.g., String, Integer) overrides these methods to provide type-specific comparison and hashing functionality.

For example:

HashMap<String, Integer> map = new HashMap<>();
map.put("Alice", 25);
map.put("Bob", 30);
map.put("Carol", 35);

String key = "Bob";
Integer value = map.get(key); // 获取与 key 关联的值

Other usage:

• Enum Key: Enumeration Classes can act as keys, they provide a fixed and meaningful set of keys.
• Composite Key: Some collections (such as ConcurrentHashMap) allow the use of composite Keys, where multiple values ​​together uniquely identify a key.
• Custom Key: Custom Key classes can be created to implement specific comparison and hashing behavior.

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