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ITEC 120
2019fall
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explorers

Due Nov.08 (Fri) 23:59. (Bring hardcopy to the following class.)

This homework adds one last function to what was originally listed. Due-date moved to Friday night, and we will talk about it in lab as well.
There will also be another assignment which builds on this, to make in interactive game.

Modeling explorers

Start a new project, and copy in your class Treasure from previous homework. We will add a second class to the same project.

An Explorer has a name, a current room, and two pockets (left and right) which each contain one Treasure.

  1. Draw a picture of three objects: two Treasures (neither of which happens to have the name lint), and one Explorer who has is carrying those treasures in its pockets. (There are no variables in this picture -- only objects.) Note that the English concept an explorer carrying a treasure is represented in our program by an Explorer object has a reference to a Treasure object.
  2. Copy/paste your picture from above, and modify it to represent what things would look like if an Explorer dropped the Treasure in their right pocket (and it disappeared), and instead their right pocket now contains lint.
    More precisely: add third Treasure object to your picture (the new lint which we want to exist), and update the Explorer's fields appropriately.
    Note that there are now three Treasures, although the Explorer has no way to get (a reference to) the dropped Treasure.
  3. Create a constructor which takes just a name. It creates a new Explorer with the given name, and lint in each pocket.
  4. Write a toString method for Explorers.
  5. Write a method String inventory(), which returns a detailed listing of the Explorer's two pockets.
  6. Write String dropLeft() which replaces the contents of the left pocket with lint and returns a String saying what happened, e.g. You drop a chocolate egg.. Similarly, write String dropRight(Treasure).
  7. Write method String grab(Treasure), which takes a Treasure as a parameter.
  8. Go back and implement a weight limit for Explorers: if an Explorer tries to grab a Treasure which would bring the combined left- and right-pocket Treasures' weights above the limit (perhaps 50lbs.), then the pocket stays the same, and it instead the method returns a message along the lines of The chocolate egg is too heavy to pick up.

  9. Write a function static readTreasure(Scanner,boolean), which has the scanner read a name, description, weight, and image-URL, and returns a new Treasure with those fields. If the provided boolean is true, then this method also prompts the user (typing at the keyboard) for the info (print one line before reading each piece of information from the Scanner). If the provided boolean is false, it does not print prompts to the user (but still reads from the keyboard).

    Tips:

    1. Use java.util.Scanner#nextLine to read each piece of info. For the weight, we're reading a String but we actually want a double; we can convert it by passing that string to java.lang.Double#parseDouble2
      Unintuitive subtlety (optional):

      You might think we should call java.util.Scanner#nextDouble instead. You certainly can do that, but if so then you'll want to immediately follow it with a(nother) call to java.util.Scanner#nextLine, for a non-obvious reason: you need to consume the newline-character that sits at the end of the number, and before the next line. Calling that funciton will return an empty-string (which you can then ignore), but it does mean your next call to nextLine will be ready to read the next line rather than the remainder of the current line (which is length 0).

      This extra work is needed, in general, only when you are mixing calls to nextLine with calls to nextDouble etc.. If you only use nextDouble() and next(), you wouldn't need to worry about this.

    2. You can call this function Scanner scan = new Scanner(System.in); followed by readTreasure(scan,true).
    3. You can also call it with a Scanner that takes its characters from a string, rather than the keyboard! readTreasure( new Scanner("a small nugget\nIt glints of gold.\n0.05\nhttps://collections.nmnh.si.edu/media/?irn=10246678"), false ) This is particularly helpful, because it lets us write some unit-tests! (Be sure to write at least two, now that you know this. You might even make one scanner that reads from a string-with-eight-lines, and make two calls to readTreasure passing it that same scanner.
    4. We'll even use it in a future assignment, to read from a file.

modeling Rooms

  1. Make a class to represent a Room: A room has 1 treasure and a description. Later, we'll add more fields: other rooms to the north, south, east, and west!

  2. Modify Explorer so that it has a current-Room.

Turn in documentation, code, and unit-tests for Explorer. (Note that Treasure wasn't actually modified for this homework, so you don't need to turn in any printouts of that class.)

As usual, follow The Design Recipe. PIs have been instructed to not help you on a method, if you don't have its comments and test-cases already written. As we've mentioned, remember to declare every field and method either public or private.

1 If you prefer, you can have grabbing a third item summarily drop one of the the two existing items: You pick up the chocolate egg, dropping a multi-colored pen.      ↩
2 Or, Object120.toDouble(String), which is actually just a non-standard name for Double.parseDouble(String).      ↩

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