DI using var's and partial functions

gistfile1.java

object HttpBuilder {
 var buildHttp: () => HttpThingIntf = new NormalHttpThing
}

// I want to change what is built by the HttpBuilder:

HttpBuilder.buildHttp = () => new MockHttpThing

// And to build a new HttpThing:

val myHttpThing = HttpBuilder.buildHttp()

// You can extend the paradigm with PartialFunctions:

object HttpBuilder {
 var buildHttp: PartialFunction[Unit, HttpThingIntf] = {
   case _ => new NormalHttpThing
 }
}

// And you can modify the functionality with a conditional:

HttpBuilder.buildHttp = {
 case _ if someCondition => new Condition1HttpMock
 case _ if someOtherCondition => new Condition2HttpMock
} orElse HttpBuilder.buildHttp