Asteroids Advice!

Design and Implementation Suggestions

Working with Random Numbers

• The class java.util.Random should be used to generate pseudo-random numbers for this application. The nextDouble method returns a double selected uniformly from the interval [0, 1). This method can be used to generate initial poses by multiplying the generated values by the desired upper bound for each component of the pose.

• In order to create a block that occurs with a particular probability, you can compare the output of nextDouble to the desired probability. For example:

  if (generator.nextDouble() < .75)
  { 
      // This block will execute with probability .75. 
  }
  

Screen Coordinates

By default, StdDraw places (0,0) at the lower-left corner of the screen. The basic units established in GameDriver are pixels, so that (10, 30) would represent a position near the lower-left corner of the screen, 10 pixels from the left and 30 pixels from the bottom.

Miscellaneous Advice

• Make sure you understand the provided code. Take some time to look over the StdDraw library documentation as well as the other provided classes.
• Test your code incrementally. Make sure that each new game element is working correctly before you start coding the next one.
• Look for opportunities to use polymorphism and dynamic binding to avoid code duplication. As always, if you find yourself copying and pasting code there is a good chance you are doing something wrong.
• Don't wait until after the UML deadline to start working on your code. You can experiment with developing and testing classes even if you haven't completely solidified your design. It will probably be easier to refactor functional code to match an improved design than it would be to start coding from scratch.

• You may find it convenient to store your game elements in one or more ArrayLists. When the elements are destroyed, you will then want to remove them. Unfortunately, modifying Java collections during iteration can lead to problems. For example, the following code will will result in a ConcurrentModificationException:

  ArrayList<String> words = new ArrayList<>();
  
  words.add("tree");
  words.add("car");
  words.add("house");
  
  // Attempt to remove "tree" from the list.
  for (String word : words)
  {
      if (word.equals("tree"))
      {
          words.remove(word); // Throws exception!
      }
  }

  Iterators may be used to safely remove objects. The following code works correctly.

  ArrayList<String> words = new ArrayList<>();
  
  words.add("tree");
  words.add("car");
  words.add("house");
  
  Iterator<String> it = words.iterator();
  
  // Remove "tree" from the list.
  while (it.hasNext())
  {
      String current = it.next();
      if (current.equals("tree"))
      {
          it.remove(); // Safely removes the most recent item.
      }
  }
  

  Another possiblity is to use an indexed for loop that indexes backwards through the collection:

  ArrayList<String> words = new ArrayList<>();
  
  words.add("tree");
  words.add("car");
  words.add("house");
  
  // Remove "tree" from the list.
  for (int i = words.size() - 1; i >= 0; i--)
  {
      if (words.get(i).equals("tree"))
      {
          words.remove(i);
      }
  }

  It is necessary to work backwards because removing an element from an arraylist changes the index of all subsequent elements: they end up being shifted down by one position. A loop that works forward through the list will end up skipping elements after a removal.