Computer Science 252
Problem Solving with Java

Fall 2015, The College of Saint Rose

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Agenda

• Announcements
  • No class meeting - power outage in our lab
  • I am available by email (but not on campus) all day today, and will have my regular office hours tomorrow afternoon
  • Lab 4: Objectdraw Practice now due next Wednesday, so we have time to learn what you need to know on Tuesday
• Review labs continue
  • Lab 1: Java Review, Part 1 due tonight
  • Lab 2: Java Review, Part 2 due in a week
  • Lab 3: Java Review, Part 3 due in 2 weeks, discussion next week
• A collection of examples to look at on your own (see the list below, and topic notes for discussion of those examples)

Lecture 4 Assignment

Due at the start of class, Tuesday, September 15.

Please submit answers to these questions in Submission Box under "LA4" or in hard copy by the start of our next class. We will discuss these questions at the start of class, so no late submissions are accepted. Please be sure that your name is clearly indicated in all submissions.

1. (Hand this question in on paper next class even if you use electronic submission for the rest.) Print a copy of the code from the CrazyColorfulSpiralLines example and label an example of each of these constructs: (i) a method call, (ii) a mouse event handler method, (iii) a local variable declaration, (iv) a formal parameter, (v) a class name, (vi) a class comment, (vii) a method header, (viii) an object construction, (ix) an actual parameter, (x) an instance variable declaration. (10 points, 1 each)
2. Write a program called ElapsedTime that displays, in a Text object on the canvas, the number of seconds between the most recent two mouse clicks.

   Note that System.currentTimeMillis returns the number of milliseconds since some fixed time in the past, as a long value. In case you haven't used them, long values work just like int values but can store a much larger range of values (2⁶⁴ values rather than the 2³² that can be stored by ints).

   If you know the return value of System.currentTimeMillis at some time in the past, the number of milliseconds since that time can be computed by the difference between the current return of System.currentTimeMillis and that previous return value.

   Hint: this is a lot like the ClickCounter example, except the number you are to display is not the counter, but the result of the subtraction of the previous click time from the current click time.

   Note: this is a restatement of BDM Exercise 5.8.1, p. 149. (10 points)

3. Summarize in a sentence or two when a variable should be declared as an instance variable and when it should be declared as local to the method in which it is used. You may include your answer on your sheet of paper for the first question, or in the comment at the top of your program for the second question. (2 points)

Terminology

• conditional statement
• condition
• boolean expression
• relative location
• absolute location

Examples

• ClickCounter
• Rectangles
• ColorfulSpiralLines
• MoreColorfulSpiralLines
• CrazyColorfulSpiralLines