[jcelerier]

> No, the main reason we want DI is to change the behaviors based on what's passed.

but which behaviours are passed depend on something external to the system - config files, etc. - so you need something that gets the information from somewhere and instantiates the correct class - and trust me, you don't want to write

    Protocol proto = null;
    if(config == "protocolA")
      proto = new ProtocolA;
    else if(config == "protocolB")
      proto = new ProtocolB;
    else if(config == "protocolC")
      proto = new ProtocolC;
    else if(config == "protocolD")
      proto = new ProtocolD;
    else
      throw whatever;

    return new MyObjectWithDependencies(proto);

especially when your system supports >50 protocols, and your object also needs a logger which can itself be of 12 different kinds, a file accessor which can mmap or not according to configuration & os, etc etc