lecture 8/checking arguments

check.java

 /*
+----------------------+       ||                   +--------------+
| Client Module        | --- program to  ------>    | ITemperature |
+----------------------+       ||                   +--------------+
                               ||                           ^
                               ||                           | implements 
                               ||                           |
                               ||          +----------------+-------------+
                               ||          |                |             |
                               ||     +------------+    +---------+     +--------+
                               ||     | Fahrenheit |    | Celsius |     | Kelvin |
                               ||     +------------+    +---------+     +--------+
 */

class Client {
  public static void main(String argv[]) {
    ITemperature k = ITemperature.checked_builder(1,"K"); 
    ITemperature f = ITemperature.checked_builder(1,"C"); 

    System.out.println(k.less_than(f) + " should be true (K less F)"); 
    System.out.println(f.less_than(f) + " should be false (F less F)"); 
  }
}

// =============================================================================
// =============================================================================

interface ITemperature {
  // is `this` temperature less than `t`
  boolean less_than(ITemperature t);

  static ITemperature checked_builder(double t, String s) {
    if ( (s.equals("K")) && (t < 0))
      throw new RuntimeException("t K does not exist");

    if ( (s.equals("F")) && ((t - 32) / 1.79999999 + 273.15 < 0) )
      throw new RuntimeException("t F does not exist");
    
    return ATemperature.builder(t,s);
  }
}

// -----------------------------------------------------------------------------
abstract class ATemperature implements ITemperature {

  // ---------------------------------------------------------------------------
  // check assumptions first, then call workhorse 
  
  // ---------------------------------------------------------------------------

  public static ITemperature builder(double t, String s) {
    if (s.equals("K"))
      return new Kelvin(t);
    else if (s.equals("F"))
      return new Fahrenheit(t); 
    else
      throw new RuntimeException("bad temp. kind"); 
  }

  public boolean less_than(ITemperature t) {
    Kelvin this_normal = this.normalize();
    Kelvin t_normal    = ((ATemperature)t).normalize();
    return this_normal.less_than_normal(t_normal); 
  }
  
  protected abstract Kelvin normalize(); 

  protected boolean less_than_normal(Kelvin t) {
        throw new RuntimeException("n/a");
  }
}

// -----------------------------------------------------------------------------
class Fahrenheit extends ATemperature {
  double f;

  Fahrenheit(double f) {
    this.f = f;
  }
  
  protected Kelvin normalize() {
    double g = (this.f - 32) / 1.79999999 + 273.15;
    return new Kelvin(g); 
  }
}

// -----------------------------------------------------------------------------
class Kelvin extends ATemperature {
  double k;
  
  Kelvin(double k) {
    this.k = k;
  }

  protected boolean less_than_normal(Kelvin t) {
    return this.k < t.k; 
  }
  
  protected Kelvin normalize() {
    return this; 
  }
}