Topic: Here's how we program in Java. Actually, this is just the C-ish subset of Java; it is not much object-oriented. We will look into the object-oriented features in Chapters 1–3.

Examples Developed in Class

August 27, 2012

• Hello.java
• Loops.java
• Interact.java

These examples are also available on merlin.iue.edu in the directory /home/info/share/c243/java-review-2012-08-27

Discussion Notes

Appendix A: Java Review

A1 First Program

• Figure A.1: A1Hello.java (restricted access) — restricted to IU East students in CSCI-C243; see Oncourse Modules (the module for the first week) for details.

A2 Variables and Types

• (p. 522) Fig A.2: A2Hello.java (restricted access)
  • What are the variables and their types?
  • What does + do?
  • How to change name to an array of strings?

A3 Loops

• (p. 524) Fig. A5: A5While.java (restricted access)
  • How do we run this to greet three persons?
• Figures A6–A9: How is each different?
  • A6: A6DoWhile.java (restricted access)
  • A7: A7For.java (restricted access)
  • A8: A8For.java (restricted access)
  • A9: A9For.java (restricted access)
• How many would prefer having only one type of iteration control statement? Which one would that be?

A4 User Interaction

p. 526 Creating a Scanner (java.util.Scanner)

• Using it to read a line (a String), an int, a double, etc.

  nextLine()
  nextInt()
  nextDouble()

• Use nextLine() to clear the rest of a partially read line.
• Do exercise A.11, p. 526
  • ExA11HelloInput.java (restricted access)

A5 Branching

• Ask?
• p. 528 multiway if statement
  • If.java (restricted access)
• p. 529 switch statement
  • Switch.java (restricted access)
  • Is it any better or worse?
  • When would you recommend if, when switch?
  • Give an example of an if statement that can't be rewritten as a switch, or where using if is better than switch
    • Hint: switch (expr) case k: ... requires k to be a constant; the same expr is compared to a constant in each case; and the expr is evaluated only once.

Recursion

We can use the if statement to define recursive functions. - Explain recursion, base case, recursive step. - Example, to be developed in class: computing 2ⁿ. - Solution: PowerOf2.java (restricted access)

A6 Methods

• p. 530 Fig. A14: A14Guess.java (restricted access)
  • In detail, what happens when execution reaches line 16?
• p. 531 Exercises A14–15 (skip)

A7 Constants

(Ask)

• p. 533 fig. A17:
  • Where's the constant?
  • Explain everything on the line that declares the constant.
  • Where is the constant used?
  • Why is it sometimes a good idea to create a constant naming an instance of Scanner?
  • Exercise A16

A8 Operators

p. 536: Exercises A17–A20

A9 Debugging

• p. 537 How do we go to a specific line in our text editor?
  • Well, it depends on the text editor!
  • In Emacs, 3 ways:
    • Arrow down, watching line number on status bar
    • M-g g〈line_number〉RET
    • After compiling with M-x compile RET, use C-x ` (backquote) to go to next error message.
• Have we ever used println statements or equivalent (see bottom of page) for debugging or testing?
• We can change System.out to System.err ...
• p. 538 Have we ever used assertions?
  • What does the assertion do?
  • Why are assertions better than if/print?
  • How do we enable assertions?
  • Exercise A22
• Have we ever used an interactive debugger?

A10 Coding Conventions

(Have a look at our coding standards.)

• Rules for identifiers:
  • constants
  • class names ["CamelCase"]
  • variable and method names
  • "Standard identifiers": i, j, k, result, etc.
  • Otherwise variable names should be meaningful.
• Blocks
  • No, you do not always have to use {} for one-liners.
  • Indent correctly!
• Comments

  • Notation:

    // Comment
    /* Comment */
    /** Javadoc comment */

  • Where should we use javadoc comments?
  • How do we generate HTML documentation files from the javadoc comments?
  • See p. 541 for an example of the HTML javadoc output
• Access levels
  • Defer to chapter 3
• Arrangement of class members
  • These are some good rules; follow them!
• Exercises A23-24.

Revision log

• 2010 Sep 1B. Added link to solution of recursion problem.
• 2010 Sep 1A. Added link to coding standards, and a small section on recursion.
• 2010 Aug 30. Reformatted, with markdown.
• 2008 Aug 25. Minor edit.
• 2007 Sept 5. Initial version?