Introduction to Programming: Answers to Exercises for week 6

In the directory /import/teaching/BSc/1st/ItP/grommets you found two .class files: Grommet.class and Machine.class.

A Machine object had five public methods:

int getSpeed()
int getTemp()
void addFuel(double)
void addCoolant(double)
Grommet pushButton()

A Grommet object had two public methods:

int getQuality()
double getWidth()

A Machine object could be constructed with a zero argument constructor.

This represented a situation in which machines produce grommets. Any machine at any particular time had a temperature and a speed which may be changed by adding fuel to it or adding coolant to it. You could assume adding fuel will always cause the speed to increase and adding coolant will always cause the temperature to decrease. The methods getSpeed and getTemp returned the speed and temperature of a machine, while addFuel and addCoolant represented adding amounts of fuel and coolant (assume the amounts are in grammes) to a machine.

The machine method pushButton represented pushing a button that made the machine produce a grommet. The grommet was represented by a Grommet object. A machine's temperature and speed was slowed down when it produces a grommet. In this simulation, there were only two aspects of a grommet we were interested in: its quality which is given as an integer value, and its width which is a floating point value. These value could be obtained in the simulation by calling the getQuality and getWidth methods. A Grommet object was immutable, so the result of these methods when applied to a particular Grommet object never varied.

Machines were independent of each other, so calling any method on one Machine object wouldn't affect any other machine object (note, the ability to have class variables which in Java are defined as static variables means this can't be assumed).

The example below was given, of a program that represents starting a new machine, adding 10g of fuel then 5g of coolant, and making it produce a grommet. The quality of the grommet was then printed.

class UseMachine0
{
 public static void main(String[] args)
 {
  Machine m1 = new Machine();
  m1.addFuel(10);
  m1.addCoolant(5);
  Grommet g1 = m1.pushButton();
  System.out.println("Grommet quality is: "+g1.getQuality());
 }
}

In this exercise you should have written programs that represented the scenarios given. The answers which should be produced if the .class files from /import/teaching/BSc/1st/ItP/grommets were used were also given. You were not expected to write your own Machine.java and Grommet.java files.

1) Write a program that starts a machine, adds 15g of fuel then 12g of coolant, and then prints the resulting temperature of the machine.

Expected answer: Temperature is: 47

Code:

class UseMachine1
{
 public static void main(String[] args)
 {
  Machine m1 = new Machine();
  m1.addFuel(15);
  m1.addCoolant(12);
  System.out.println("Temperature is: "+m1.getTemp());
 }
}

2) Write a program that starts a machine, keeps adding fuel to it in 5g amounts until its temperature is over 60, then prints the resulting speed of the machine.

Expected answer: Speed is: 828

Code:

class UseMachine2
{
 public static void main(String[] args)
 {
  Machine m1 = new Machine();
  while(m1.getTemp()<=60)
     m1.addFuel(5);
  System.out.println("Speed is: "+m1.getSpeed());
 }
}

3) Write a program that starts a machine, keeps adding fuel to it in 5g amounts until its speed is over 1000, and then keeps adding coolant to it in 3g amounts until its temperature is under 55. Then it prints the speed of the machine.

Expected answer: Speed is: 804

Code:

class UseMachine3
{
 public static void main(String[] args)
 {
  Machine m1 = new Machine();
  while(m1.getSpeed()<=1000)
     m1.addFuel(5);
  while(m1.getTemp()>=55)
     m1.addCoolant(3);
  System.out.println("Speed is: "+m1.getSpeed());
 }
}

4) Write a program that starts a machine, makes it produce two grommets and prints the quality of whichever of the grommets has the greatest width.

Expected answer: The quality of the widest grommet is: 15

Code:

class UseMachine4
{
 public static void main(String[] args)
 {
  Machine m1 = new Machine();
  Grommet g1,g2;
  int quality;
  g1=m1.pushButton();
  g2=m1.pushButton();
  quality=g1.getWidth()>g2.getWidth()?g1.getQuality():g2.getQuality();
  System.out.println("The quality of the widest grommet is: "+quality);
 }
}

5) Write a program that starts a machine, makes it produce 100 grommets, and prints the average width of the grommets.

Expected answer:Average width is: 1.5074199999999993
(there are ways to get floating point numbers formatted in Java so they don't print out a silly number of decimal places, but you needn't use them here).

Code:

class UseMachine5
{
 public static void main(String[] args)
 {
  Machine m1 = new Machine();
  int i=0;
  double sum=0;
  while(i<100)
     {
      sum+=m1.pushButton().getWidth();
      i++;
     }
  System.out.println("Average width is: "+sum/100);
 }
}

6) Write a program that starts a machine, makes it produce 100 grommets, and prints the average width of all the grommets whose quality is over 17.

Expected answer: Average width is: 1.5109166666666676

Code:

class UseMachine6
{
 public static void main(String[] args)
 {
  Machine m1 = new Machine();
  int i=0,count=0;
  double sum=0;
  while(i<100)
     {
      Grommet g1 = m1.pushButton();
      if(g1.getQuality()>17)
         {
          sum+=g1.getWidth();
          count++;
         }
      i++;
     }
  System.out.println("Average width is: "+sum/count);
 }
}

7) Write a program that starts two machines. To one it adds 50g of fuel followed by 16g of coolant, to the other it adds 50g of fuel followed by 13g of coolant. It produced 100 grommets from each, and says which produces the higher quality grommets on average.

Expected answer: The machine which starts with 50g of fuel and 16g of coolant produces the better grommets

Code:

class UseMachine7
{
 public static void main(String[] args)
 {
  Machine m1 = new Machine(), m2 = new Machine();
  int i=0,sum1=0,sum2=0;
  m1.addFuel(50);
  m1.addCoolant(16);
  m2.addFuel(40);
  m2.addCoolant(13);
  while(i<100)
     {
      sum1+=m1.pushButton().getQuality();
      sum2+=m2.pushButton().getQuality();
      i++;
     }
  System.out.print("The machine which starts with ");
  if(sum1>sum2)
     System.out.print("50g of fuel and 16g of coolant ");
  else
     System.out.print("40g of fuel and 13g of cooleant ");
  System.out.println("\nproduces the better grommets");
 }
}

8) Write a program that starts a machine and produces 200 grommets. If at any time after producing a grommet the speed of the machine is below 300, it keeps adding 3g of fuel followed by 1g of coolant until the speed is above 700 before producing the next grommet. At the end, it prints how much fuel in total has been aded.

Expected answer: Total fuel added: 189g

Code:

class UseMachine8
{
 public static void main(String[] args)
 {
  Machine m1 = new Machine();
  int count=0,totalFuel=0;
  while(count<200)
     {
      Grommet g1 = m1.pushButton();
      if(m1.getSpeed()<300)
         while(m1.getSpeed()<=700)
            {
             m1.addFuel(3);
             m1.addCoolant(1);
             totalFuel+=3;
            }
      count++;
     }
  System.out.println("Total fuel added: "+totalFuel);
 }
}

9) Write a program that starts two machines. To one it adds 60g of fuel followed by 35g of coolant, to the other it adds 50g of fuel followed by 25g of coolant. It then produces 100 grommets from each. After this, it adds 30g of fuel followed by 10g of coolant to whichever machine produced the higher quality grommets on average. Then it produces 100 more grommets from that machine and prints the average width of this further 100.

Expected answer: Average width is 1.50715

Code:

class UseMachine9
{
 public static void main(String[] args)
 {
  Machine m1 = new Machine(), m2 = new Machine(), m3;
  int i=0,sum1=0,sum2=0;
  double sum3=0;
  m1.addFuel(60);
  m1.addCoolant(35);
  m2.addFuel(50);
  m2.addCoolant(25);
  while(i<100)
     {
      sum1+=m1.pushButton().getQuality();
      sum2+=m2.pushButton().getQuality();
      i++;
     }
  m3=sum1>sum2?m1:m2;
  m3.addFuel(30);
  m3.addCoolant(10);
  i=0;
  while(i<100)
     {
      sum3+=m3.pushButton().getWidth();
      i++;
     }
  System.out.println("Average width is "+sum3/100);
 }
}

10) Write a program that starts two machines. To one it adds 70g of fuel followed by 50g of coolant, to the other it adds 65g of fuel followed by 30g of coolant. It then produes 100 grommets in total. Each grommet is produced from whichever machine has the highest speed at the time the grommet is to be produced, with a new test of speeds for the next grommet. It then prints how many grommets each machine has produced.

Expected answer:

The machine that started with 70g of fuel and 50g of coolant produced 42 grommets.
The machine that started with 65g of fuel and 30g of coolant produced 58 grommets.

Code:

class UseMachine10
{
 public static void main(String[] args)
 {
  Machine m1 = new Machine(), m2 = new Machine();
  int count1=0,count2=0;
  double sum3=0;
  m1.addFuel(70);
  m1.addCoolant(50);
  m2.addFuel(65);
  m2.addCoolant(30);
  while(count1+count2<100)
     if(m1.getSpeed()>m2.getSpeed())
        {
         m1.pushButton();
         count1++;
        }
     else
        {
         m2.pushButton();
         count2++;
        }
  System.out.print("The machine that started with 70g of fuel ");
  System.out.println("and 50g of coolant ");
  System.out.println("produced "+count1+" grommets");
  System.out.print("The machine that started with 65g of fuel ");
  System.out.println("and 30g of coolant ");
  System.out.println("produced "+count2+" grommets");
 }
}

Matthew Huntbach

14th December 2000