Overview

• Preliminaries.
  • Admin.
  • Upcoming Work.
  • Extra Credit.
  • Questions.
• Labs.

Preliminaries

Admin

• Continue partners.
• Two labs, but both short.
• I'll try not to talk much today (after the preliminaries).
• I sent out notes on HW 3 yesterday. Please do take the time to read them, as they apply to many of your assignments.
• I sent out some comments on HW 4 yesterday. I'll take additional questions at the end of the preliminaries.
• I sent out peer review links yesterday. It sounds like some of you didn't get them. I'll resend if you email me.
• I brought a few more copies of the HFOSS survey. I would like you to fill it out if you are willing. (No bribes for doing so, other than an expectation of cookies in a future class.)

Upcoming Work

• Daily lab writeup: http://bit.ly/207writeup
• Readings for Tuesday
  • Debugging in Eclipse
• HW 4 due tomorrow night.

Campus Events of Interest

• Become a Peer Advisor in CS (PACS?)
• Rosenfield seminar on Scotland, Tuesday noon and Thursday afternoon.
• Rosenfield internship talks, Wednesday and Thursday.
• Rebecca Hamlin book talk Wednesday at 4:15 pm.

Extra Credit Opportunities

Academic

• Convo Wednesday: President Kington
• CS resume review session, Thursday, 4:30 pm.
• CS Table, Friday: User Tracking

Peer Support

• CS Extras Thursday the 25: ZW and EF, and AHD, and others on MIST.

Miscellaneous

• Project IGNITE!

Questions

• Can we use vectors in the segmenting strings problem?
  • Sure. As long as your return an array.
• Can you go through the long string example?
  • Yes. See whiteboard.
• Do we have to support negative numbers in our calculator?
  • Yes, except for exponents. It can crash for negative exponents.
• Do we have to support fractional exponents?
  • No. (Hmmm ... okay, you don'thave to support exponentiation in your fractional calculator.)

• How does the weirdo equals method work.

  class Fraction
  {
    BigInteger num;
    BigInteger denom;
  
  
    ...
    public boolean equals(Object other)
    {
      // If the objects occupy the same area of memeory, they are
      // the same
      if (this == other)
        {
          return true;
        } // this == other
      // If the other object is a Fraction
      else if (other instanceof Fraction)
        {
          return this.equals((Fraction) other);
          // Fraction frac = (Fraction) other;
          // return this.num.equals(frac.num) && 
          //    this.denom.equals(frac.denom);
        } // other is a Fraction
      // If the other object is a BigInteger
      else if (other instanceof BigInteger)
        {
          return this.equals((BigInteger) other);
        } // other is BigInteger
      // Everything else is different.
      else
        return false;
    } // equals(Object)
  
  
    /** 
     * Determine if this fraction is the same as a BigInteger.
     * A fraction is the same as a BigInteger when the denominator
     * of the fraction is 1 and the numerator is the same as the
     * BigInteger.
     */
    public boolean equals(BigInteger other)
    {
      return this.denom.equals(BigInteger.ONE) &&
        this.num.equals(other);
    } // equals(BigInteger)
  
  
    /** 
     * Determine if this fraction is the same as another fraction.
     * Two fractions are the same if they have the same numerator
     * and denominator.
     */
    public boolean equals(Fraction other)
    {
      return this.num.equals(other.num) && 
         this.denom.equals(other.denom);
    } // equals(Fraction)
  
  
  } // class Fraction
  
  
  checkEquals(new Fraction(1,2), Calculator.eval1("1/2"));
  
  
  // How JUnit deals with this.
  //   Evaluate the first value, call it v1
  //   Evaluate the second value, call it v2
  //   Call v1.equals(v2)
  //     If true, does nothing
  //     If false, reports an error
  //   JUnit assumes v1 and v2 are objects
  //   So Java looks for a method with signature equals(Object)
  //     to do the comparison.
  
  
  checkEquals(new Fraction(1,2).toString(), Calculator.eval1("1/2").toString());
  

• When we put the simplify method (using gcd) in the constructor, does it need to be anywhere else?

  • If you only have one constructor, no.
  • If you have multiple constructors, it probably needs to happen in all of them (or all appropriate ones).

• Can we call constructors from other constructors?

  • Yes

    public Fraction(BigInteger num, BigInteger denom) { this.num = num; this.denom = denom; } // Fraction(BigInteger, BigInteger)

    public Fraction(int num, int denom) { this(new BigInteger(num), new BigInteger(denom)); } // Fraction(int, int)

Reference values vs. primitive values

Some typical misunderstandings

Primitive types and their corresponding classes

Automatic boxing and unboxing