Exercises

"Predicate" methods
(Methods/services/commands that have a return value)

Note: Please keep the programs that you create today, in case you have a dispute about your grades for the ICEs at the end of the quarter. When you're working with a partner, each person should save their own, individual copy

Part 1: Predicate Methods

For each of the following examples, write out exactly what is printed when the program is run.

You must do this for each program, even if it does not compile - in that case, make sure to explain what the program WOULD do, if it was run (despite the compile errors)

class PrintHelper extends Object
{
    public int firstService()
    {
       return 1;
    }
}

public class FileName extends Object
{
public static void main(String[] args)
{
    PrintHelper ph = new PrintHelper();
    int num;
    num = ph.firstService();
    System.out.println( num );
}
}

class PrintHelper extends Object
{
   public double service2()
   {
    return 3.14 + 1;
   }
}

public class FileName extends Object
{
public static void main(String[] args)
{
    PrintHelper ph = new PrintHelper();
    double num;
    num = ph.service2();
   System.out.println(num);
}

}

class PrintHelper extends Object
{
   public double methodThree()
   {
      double temp = 3.14 + 1;
      return 1;
      System.out.println("Hi");
   }
}

public class FileName extends Object
{
public static void main(String[] args)
{
   PrintHelper ph = new PrintHelper();
   System.out.println(ph.methodThree());
}
}

class PrintHelper extends Object
{
   public double svc4( double num)
   {
      while(num < 3)
    {
                  num = num * 2;
                }
      return num;
   }
}

public class FileName extends Object
{
public static void main(String[] args)
{
   PrintHelper ph = new PrintHelper();
   System.out.println( ph.svc4(2) + ph.svc4(3));
}

}

class PrintHelper extends Object
{
   public double method5(double num)
   {
    System.out.println( "Will this Print?");
    System.out.println( "What about this?");
      return num;
   }
}

public class FileName extends Object
{
public static void main(String[] args)
{
    PrintHelper ph = new PrintHelper();
    System.out.println(ph.method5(2));
}

}

class PrintHelper extends Object
{
   public double svc6(double num)
   {
      double temp = num + 2;
      if( temp > 0)
        return temp;
    System.out.println( "Will this Print?");
    System.out.println( "What about this?");
    return 1.0;
   }
}

public class FileName extends Object
{
public static void main(String[] args)
{
      PrintHelper ph = new PrintHelper();
     System.out.println(ph.svc6(2));
}

}

class PrintHelper extends Object
{
   public boolean svc7(double num)
   {
      if( num >= 0 )
    {
            return true;
    }
    else
    {
            return false;
    }
   }
}

public class FileName extends Object
{
public static void main(String[] args)
{
    PrintHelper ph = new PrintHelper();
    boolean b;
    b = ph.svc7(-7.76);
    if( !b )
    {
     System.out.println( "Number is valid");
    }
    else
    {
        System.out.println( "Number is so negative, it's not funny");
    }
}

}

class PrintHelper extends Object
{
public boolean methodEight(double num)
{
    if( num >= 0 )
    {
        return true;
    }
    else
    {
        return false;
    }
    System.out.println( "Will this Print?");
}
}

public class FileName extends Object
{
public static void main(String[] args)
{
    PrintHelper ph = new PrintHelper();
  if(ph.methodEight(7.76) )
    {        System.out.println( "Number is valid");
    }
    else
    {
        System.out.println( "Number is so negative, it's not funny");
    }
}

}

Part 2: Tracing a Predicate Method

After watching the instructor's demo, download the Java program named FileName.java, and trace through it, paying special attention to the return statement.

Part 3: Creating Predicate Services

Download the file ICE_14_Part_1_Test.java, and write the predicate service called isNorthOfStreet(int st) This tests whether a robot is north of the street indicated by the parameter st. The method should return true if the robot is north of the street, and false if it isn't.

You should make sure to test your new command by creating the robot on, say, street 2, facing north. You should then ask if the robot is north of street 1(it isn't), if it's north of street 3 (it should be), and if it's north of street 2 (it isn't).

Once you've done that, create a second, similar service to tell you if the robot is south of a given street:

isSouthOfStreet(int st);

Make sure to test your new robot out by trying it out in various ways. For example, you might put it on street 5, and try calling isNorthOfStreet(10), isNorthOfStreet(0), and isNorthOfStreet(5).