What is Inversion of Control (IoC) and Dependency Injection (DI)?

Inversion of Control (IoC) is a design paradigm where the control flow of the program is delegated to an external component or framework, rather than being explicitly defined within the object. The object delegates the responsibility for creating, configuring, and managing its dependencies to this external element.

Dependency Injection (DI) is a specific pattern of implementing IoC. The essence of DI is that the dependencies of an object are provided from outside, rather than created by the object itself. This is achieved by passing dependencies through constructors, setter methods, or fields.

Key differences:

Characteristic	Inversion of Control (IoC)	Dependency Injection (DI)
Scope of definition	Broader concept	Specific IoC pattern
Mechanism	Delegation of control	Passing dependencies from outside
Goal	Reduce coupling, increase flexibility	Simplify testing, support reuse

Example of DI via constructor:

class Service {
    private Dependency dependency;

    // Dependency is injected via constructor
    public Service(Dependency dependency) {
        this.dependency = dependency;
    }

    public void doSomething() {
        dependency.performAction();
    }
}

class Dependency {
    public void performAction() {
        // Dependency logic
    }
}

// External code creates and links objects
Dependency dependency = new Dependency();
Service service = new Service(dependency);
service.doSomething();

Advantages of IoC/DI:

• Reduced coupling: Components depend less on each other, making them easier to change and replace.
• Increased flexibility: Easier to change dependency implementations without modifying the code that uses them.
• Simplified testing: Dependencies can be easily replaced with "mock objects" for isolated testing of components.
• Improved maintainability: Code becomes more modular and understandable.
• Support for reuse: Components become more versatile.