Assignment 4

pop 25 ;
infected 3 ;
house 3 , 1 ;

house 4 , 3 ;
infected 2 ;
pop 12 ;

house 4 , 3 ; // this is a range from 1 to 7

~dwjones/submit SECTION Epidemic.java

~dwjones/format Epidemic.java

public enum boolean { false, true }

Note that the infeciton declaration could look just like the above, but with a longer list of possible values.

Reading the assignment closely, each person has an infection state, so for the requirement to print out the population, it makes sense to print out for each person, not only their home but their infection state. Nothing in the assignment asks you to print out a list of all the people in each infection state. Infection states aren't places.

Ultimately, in the simulation, we will need to count the number of people in each place who are contageous or bedridden, because that count is part of determining the likelihood that an uninfected person will be infected when they enter that place.

Note that the only two relevant infection states for the purpose of initializing the populatio are are uninfected and latent. The latter is the initial state of an infected person. As the infection progresses, it will go through other states. Later, when we start simulation, we will need the other states.

This is the kind of question that is very typical of the early stage of the development process. The folks who wrote the specification never imagined issues of what was algorithmically easy, so it never occurred to the to specify something like this. Now that you notice this, note:

• If you place people in families sequentially, as in the distributed solution to MP1, then infecting people sequentially always lumps the first infections into the same family or families. This might have an impact on the outcome.
• If, on the other hand, you place people into random families as they are created, then infecting the first n people distributes the infection randomly over the community.

Which is right? It is unlikely that the folks who wrote the spec (me) were asking for initial infections to be lumped in just a few families. For an infectious disease, infecting one person in a family frequently infects the whole family a short time later, so this is an unlikely interpretation of the specification. So, it is better to spread the initial infections more or less at random over the population.

Bare minimum requirement: The program header must credit both of us. If you take my solution to MP1 and add your code to make it solve MP2, then credit me first, you second.

In more detail, as the blending of code gets more complex, it becomes appropriate to add @author tags to the Javascript comments on individual classes or even on individual methods. Any class that's 100% your code should have just your tag, while classes of mine that you modified can have both tags, and classes you didn't change just have my tag.

If someone writes 25 pop instead of pop 25 don't try to make sense of it, it's just completely wrong. On the other hand, it must not throw an exception. It might say something like unknown command: 25 and then go on from there. Don't write massive code trying to make sense of wrong input.

Neither! There is no obvious default value. Your program must output an appropriate error message and terminate gracefully indicating that it is a failure. You can only do this with a call to System.exit(1) (actually, any nonzero value will suffice, and the value 2 is historically associated with the "no such file" message). You may throw an exception internally to handle this, but you must catch it. The default behavior of Java for unhandled exceptions is unacceptable.

I talked about this in lecture. We have two error handlers in the code I included in the lecture and posted on line last week. Error.fatal() outputs a message and kills the program on the spot. Error.warn() allows the program to stumble onward.

We will talk later about killing the simulation if there were warnings. For now, syntax errors in the input file should be handled with warnings. You might look at the bug messages in my code though for a suggestion that if there are too many warnings, perhaps the code should give up instead of outputting a cascade of messages.

You need to recall the purpose of the output. Until we build a working simulation, the only purpose of the output we are creating is to debug the model. How can you know how well you have assgined the initial infection state if you do not include this in your dump of the population? So, when you print out the collection of people, of course you need to include not only where each person lives but their infection state.

As discussed in class, it would be nice to get rid of this space, but to do that nicely, we need to explore deep things inside class Scanner. Until we do so, it is not worth the effort.

Error messages should be brief but helpful. I recall one piece of software I I used where the only error message was "?". This was not very helpful. I recall other software that had the anoying tendency to produce miniature essays on the nature of each error. That was annoying because it tended to belabor the obvious.