ITEC 120 2012fall dbraffitt ibarland

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lab13a
Objects containing Objects

Self-Test:

class Blarg {
  private int zzmph;
  // &vdots;
  // Other fields/methods omitted
  // &vdots;
  }

Also, we'll see motivation today for the following rule-of-thumb, about access modifiers (public and private):
Fields should be declared                 ; almost all methods should be declared                 .

We will develop a class to represent the Hideouts that Robots use while they try to hide their presence on Earth.
Initial source files: lect13a-hideout.jar; see how-to-get-jar-files-into-BlueJ—Downloading .jar files into BlueJ.
We won't turn in today's work, though it will practice the concepts that will be needed for the last hw.

• We'll say that a Hideout contains:
  • a String address,
  • a Robot pres,
  • a Robot vp,
  • and a Robot[] crew

• Lesson: A method should process one type of data -- process nested data with helper functions.

  The reason for this is that in real programs, the data gets more complicated: It's not at all far-fetched to want to have an array of Hideouts, each containing an array of Robots, each of which contains in turn an Address object, which hold several Strings. It rapidly becomes too hard to have one method that deals with all the layers.
  So: Hideout methods should only work with the direct Hideout fields/info -- if there is code about Robots, make it a method inside class Robot!
• Write a method arrayToString which takes in an array of Robots, and returns a String: one Robot per line, with the lines numbered (starting from 1).

  Should this method be static, or not? Well, ideally, it would be a non-static method inside some class "array-of-Robot" (and we'd walk up to the array-object, and ask it to toString itself). However, there isn't really such a class in Java (!?), so we'll fake it: we'll make this a static method, which is explicitly passed in an array.

• Now, write the function Hideout#toString().
  (Note that Robot#toString() and Song#toString() are already written.)
• Complete Hideout#deepEquals(Hideout), which just compares two Hideouts, comparing field-by-field for equality¹
  (Note that Robot#deepEquals(Robot) has already been written, and that Song#equals(Song) already checks for "deep" equality.)
• In a moment, you'll write a function which swaps the president with a crew-member. On the board, together: What does the 'before' picture look like? What will the 'after' picture look like? What code is required to get from 'before' to 'after'?
• Why doesn't the following two lines of code work?:

  int a = 93 int b = 17; // Now, we try to swap the contents of these two local variables: a = b; b = a; // What do things look like?

  How can we fix this?
• A method to modify the array:

  /** Swap this Hideout's president and a crewmember. * @param crewIndex The index of which crewmember to make president. * It must be an integer in [0,this.crew.length). */ void elect( /* Hideout this, */ int crewIndex ) { /* stub */ }

  A 'Before' picture is drawn for you on the board. Draw the picture after calling elect(1).
• Complete the function coolestRobot (barely started in lecture), which returns the coolest Robot in this entire Hideout.
(You should complete the lab at least this far.)

---

• /** Swap this Hideout's president and the most popular crewmember. */ void holdElection() { ... }

  We'd like to be able to re-use coolestRobot without change, but we can't quite do that -- we need to know not just the coolest crewbot, but its index. (This will at least allow us to directly re-use elect.)
  However, we can retroactively re-factor our code to minimize work.
• Write boolean isInRevolt(), which determines whether any crew-*members* of this Hideout would attack any other crew-member.

  Hint: A handy helper method would take any Robot r and any Robot[] crowd, and determine whether r would pick a fight with any member of crowd.
  Once this is written, how can you use it to determine whether each crewmember might combat any other member of the crew?

Hideout.java (and one helper function (willBattleAnyOf) added to Robot.java)
Files/solution as completed in lecture: lect13a-sect04-hideout/.

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©2012, Ian Barland, Radford University Last modified 2012.Dec.04 (Tue)

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