What is the difference between the depencylookup and dependency injection

[sameerkumar]

Hi ,
what is the difference between dependencylookup and dependency injection.please give me an example also.
Regards,
Sameer.

[jamestastic]

In a nutshell, dependency lookup is when an object finds a way to create/instantiate/lookup its own dependencies (such as a private property).

Dependency injection is when the same object is provided the dependency by some DI framework.

Dependency lookup:

private String greeting;

public void printGreeting() {
    greeting = GreetingManager.getEnglishGreeting();
    System.out.println(greeting);
}

Dependency injection:

Imagine that there is a DI framework, such as Spring, which defines the greeting bean and injects it by calling a setGreeting(String greeting) method.

private String greeting;

public void printGreeting() {
    System.out.println(greeting);
}

The big difference is the dependency injected object doesn't worry about how to get a greeting. It leaves that up to the DI framework. The DI framework is then free to swap out different versions of the greeting for different enviroments, or testing, etc.