What are collaborators in java?

Question

hey, i was reading an article about dependency injection and it says:
"Dependency Injection has several important benefits: For example
-Because components don't need to look up collaborators at runtime, they're much simpler to write and maintain.....
- A good IoC implementation preserves strong typing, If you need to use a generic factory to look up collaborators, you have to cast the results to the desired type....
Could someone please explain what collaborators are, or give me some good references to read regarding them? Haven't really found any good explanation through google.
Thanks

Answer 1

So does that mean, in this example, the collaborators of the object Rocket are the Engine object eng and the Fuel object fuel?
public class rocket {
     private Engine eng;
     private Fuel fuel;
public rocket(Engine eng, Fuel fuel) {
     this.eng = eng;
     this.fuel = fuel;
}