What is dependancy Injection?

here's interface injection:

public class Foo

{

private Bar bar;

public void setBar(Bar b) { this.bar = b; }

}

Class Foo depends on a Bar instance. Set it using the setBar method.

Here's constructor injection:

public class Foo

{

private Bar bar;

public Foo(Bar b) { this.bar = b; }

}

Class Foo depends on a Bar instance. Set it using the Foo constructor.

Dependency injection frameworks make it possible for you to do this using declarative syntax rather than hard-wiring in your source code.

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duffymoa at 2007-7-14 1:25:27 >

>It's going over my head. Can someone describe it more clearly.

If you cannot understand the Martin Fowler article, nobody can help you.

>Why it's called Injection

Injection \In*jec"tion\, n. [L. injectio : cf. F. injection.]

1. The act of injecting or throwing in; -- applied

particularly to the forcible insertion of a liquid or gas,

by means of a syringe, pump, etc.

[1913 Webster]

Ex. Rajeev.Asthana needs an injection of magic comprehension serum.

IanSchneidera at 2007-7-14 1:25:27 >

> > Sorry, should have called that "setter injection".

>

> That's the little scabby dog that Jos was talking about?

Pa, "Old Setter" is dead! He's dead! They've killed my scabby little dog!

To the OP: Gotta help yourself here. Do some reading.

"Dependency" means that class A needs an instance of class B to do its work. A depends on B.

Still with me? Too fast?

"Injection" because you have to give class A a copy of class B. You can do that by both of the means that I showed you earlier. You can understand both of those, right? That's just Java - no framework involved.

Am I writing slowly enough for you?

The new wrinkle is that frameworks such as Spring let you spell out those dependencies declaratively in configuration files and save you from having to write a lot of plumbing code to do the injection.

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duffymoa at 2007-7-14 1:25:27 >