CSC152 2005FS, Class 13: Conditionals

Overview:
* Happy Valentine's Day!
* Reading may be available for tomorrow

Admin:
* Questions on classes?
* Basics of Booleans
* If statements
* Lab

/Types in Java/
* Primitive types: int, float, long, double, ...
* Predefined classes (including some that correspond to primitive types)
* Your own classes
* One more primitive type: boolean
  * Truth values: true, false
  * Named after George Boole: Developed "calculus" of truth values
* Interesting operations:
  Numbers n and m:
    n < m
    n > m
    n <= m
    n >= m
    n == m  ; Equal to, two signs to distinguish from assignment
    n != m  ; Not equal to
  Boolean expressions b and c
    (b && c) ; AND
    (b || c) ; OR
    !b ; NOT
  In Scheme, you have "false" and "everything else"
  In Java, a variable of type boolean can only be true or false
  In Java, when you need a boolean expression, that expression can only evaluate to true or false

* Why use booleans?
  if (boolean-expression) {
    stuff-to-do-if-the-expression-evaluates-to-true
  }
  else {
    stuff-to-do-if-the-expression-evaluates-to-false
  }
* Meaning:
  * Evaluate the boolean-expression
  * If it evaluates to true, do "stuff...true"
  * If it evaluates to false, do "stuff...false"
  * Java won't have compiled the program if it can evaluate to soemthing else

* The else part is optional, in which case you "do nothing" if the boolean expression evaluates to false
* When you want to test a sequence of expressions
  if (boolean-expression) {
    stuff-to-do-if-the-expression-evaluates-to-true
  }
  else if (another-boolean-expression) {
    stuff-to-do-if-the-first-evaluates-to-false-and-the-second-to-true
  }
  else if (yet-another-boolean-expression) {
    stuff-yadda
  }
  else {
    stuff-to-do-if-nothing-evaluates-to-true
  }
  public String method grade()
  {
    if ((!this.name.equals("ROLF") && (this.numeric > 93)) || (this.numeric >= 94)) {
      return "A";
    }
    else if (this.numeric >= 90) {
      return "A-";
    }
    else {
      return "B-";
    }
  }

DO the lab!

Be prepared to reflect

* How do you call a method within a constructor?
	this.method(params);
  For example
  	this.cleanup();

How far did you get?
* Currently working on problem 1 (no negative denominator)
* Currently working on problem 2 (simplify)
* Currently working on problem 3 (comparison)
* Currently working on problem 4 (comparison, revisited)