Besides using Spring, what are alternative methods of dependency injection in applications?

Besides Spring, inversion of control (IoC) can be implemented in the following ways:

• Using other frameworks, such as Google Guice — a lightweight DI container for Java.
• Manual dependency injection through constructors or setters without a framework.
• Using CDI (Contexts and Dependency Injection) — a Java EE standard for IoC.
• Applying factory methods and the Service Locator pattern for dependency management.

For example, with manual dependency injection, objects are created and passed explicitly:

class Service {
    private final Repository repo;
    public Service(Repository repo) {
        this.repo = repo;
    }
}
// In main or configuration
Repository repo = new Repository();
Service service = new Service(repo);

This is a simple way to achieve IoC without using Spring.