🔍 When Do You Have Many Instances of a Class in Java?

A class can have many instances when you create multiple objects from it. This happens often in Spring services, repositories, controllers, or any object-oriented Java application.

🟢 Example: Multiple Instances of a Class

Imagine a User class that represents users in an application.

❌ Bad: Non-Static Logger (Every Object Has Its Own Logger)

java
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public class User {
    private final Logger LOGGER = LoggerFactory.getLogger(User.class); // ❌ Each User object gets its own Logger
    private String name;

    public User(String name) {
        this.name = name;
        LOGGER.info("User {} has been created", name);
    }
}

📌 Problem:

• Every time you create a User object, a new Logger object is also created.
• This wastes memory and is unnecessary since all User objects log the same way.

🚀 Scenario: Creating Many Instances

java
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public class UserApp {
    public static void main(String[] args) {
        User user1 = new User("Alice");
        User user2 = new User("Bob");
        User user3 = new User("Charlie");
    }
}

📌 Output (3 separate Logger objects, unnecessary overhead):

pgsql
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INFO: User Alice has been created
INFO: User Bob has been created
INFO: User Charlie has been created

🔴 Each User instance has its own Logger, which is inefficient.

✅ Correct: Static Logger (Only One Logger Shared)

java
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public class User {
    private static final Logger LOGGER = LoggerFactory.getLogger(User.class); // ✅ Shared across all User objects
    private String name;

    public User(String name) {
        this.name = name;
        LOGGER.info("User {} has been created", name);
    }
}

🚀 Now, no matter how many User instances you create, only one Logger is used!