CS141: Topics for the Week of Nov 7, 2011

Topics & Activities

• Mon: No Technews this week!

• Chapter 6: Array Lists
  • The ArrayList class - many methods: add, get, remove, size, isEmpty, toArray
  • Benefits: can grow and shrink, Cons: takes up more space, may be slower than arrays but only an issue if size is really, really big.
  • Creating an ArrayList
    • must import java.util.ArrayList
    • ArrayList<String> myList = new ArrayList<String>(); // creates an empty list
    • Can't use primitive types, must use Object representation of primitive (wrapper):
      ArrayList<int> myNums = new ArrayList<int>(); // NOT ALLOWED
      ArrayList<Integer> myNums = new ArrayList<Integer>(); // OK
  • Setting the values of an ArrayList:
    • myList.add("hello"); // adds a single element to the end of the list
    • ArrayList myList = new ArrayList(Arrays.asList("hi","there","today")); // adds multiple elements all at once
  • Accessing or Printing the values of an ArrayList:
    • System.out.println("myList element is " + myList.toString() ) ; // prints out the list
    • Print using a loop (for-loop or enhanced for-loop), e.g.

      for (String s: myList) {
      
         System.out.println(s); 
      
         
      
      }

  • Beware - must be careful removing elements using a loop.

• A few in-class exercises (not to turn in):

  • See Basic Array Problems.

  • 2D Arrays Practice with Magic Squares: Do Problemming Exercise P6.12 in the text on p. 267. To make testing easier, it might be good to start by having the values set in the code rather then entered by the user, e.g.

     int[][] mySquare = { { 16,3,2,13}, {5, 10, 11, 8},{9, 6, 7, 12},{4, 15,14,1}}; 

    Once this works, write code to prompt the user to enter the numbers.

• In Lab:

  • Follow the instructions: Lab 10: TicTacToe, etc

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