CS141: Topics for Week 9: Oct 23, 25, 27, 2017

Computer Science Headlines: ACM Tech News

Mon & Wed: Continue from Last Week

• Finish discussion of Arrays

Reading:

• Chp 11: Input/Output and Exception Handling

Lab and Other Activities

• Continue: Lab 7: Arrays

• Practice with 2D arrays. Given the following code:

  Line 1:  Card[][] cards;
  Line 2:  cards = new Card[3][];
  Line 3:  System.out.println("cards.length = " + cards.length);
  
  Line 4:  cards[0] = new Card[2];
  Line 5:  cards[1] = new Card[4];
  Line 6:  cards[2] = new Card[3];
  
  Line 7:  for (int i=0; i < cards.length;i++) {
  Line 8:      System.out.println("i="+i+":   cards[i].length = " + cards[i].length);
  Line 9:      for (int j=0; j < cards[i].length; j++) {
  Line 10:         cards[i][j] = new Card(i*j); 
  Line 11:         System.out.println("  j="+j+":  cards[i][j] = " + cards[i][j]);
  Line 12:     }
  Line 13: }
  

  Do the following:
  • Show the picture in memory after executing lines 1,2,4,5,6,10.
  • What is the output printed (i.e. at lines 3, 8, and 10)
  • What type of variables are cards, cards[i] and cards[i][j]?
  • If the line
    System.out.println(cards[0][0]);
    were inserted between Lines 6 and 7, what output would be generated and why?
  • If the line
    System.out.println(cards[0][0].toString());
    were inserted between Lines 6 and 7, what output would be generated and why?

• ArrayLists:

  • Declaring, adding/removing elements, look at method list, copying, wrappers for primitive types.
  • Diamond <> syntax
  • Comparison with Arrays:
    • Main advantages: Can change size. Easy to remove or add items at any location in list.
    • Main disadvantages: Take up more memory. Slower. Can't contain primitives directly (must rely on "wrappers").

• Reading and Writing Files - Sample Netbeans projects:

  • Download and unzip: Files (zip file).
  • After you unzip, you should see 2 Netbeans project folders:
    • AphorismsProject: Reads a list of aphorisms into array.
    • ArrayFileExample: Shows how to read and write numbers to a file.
  • Open Netbeans and then open both of these projects.

Lecture Discussion Topics:

Concepts and Vocabulary

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