Develop Reference

Output is "NaN"

So, I have developed a class that is suppose to be used by another class. The class I developed is as follows:
public class Car
{
private double milesPerGallon;
private double gas;
//Constructs a car with a given fuel efficiency
public Car(double milesPerGallon)
{
gas = 0.0;
}
//Increases the amount of gas in the gas tank
public void addGas(double amount)
{
gas = gas + amount;
}
//Decreases the amount of gas in the gas tank (due to driving and therefore consuming gas)
public void drive(double distance)
{
gas = gas - (distance / milesPerGallon);
}
//Calculates range, the number of miles the car can travel until the gas tank is empty
public double range()
{
double range;
range = gas * milesPerGallon;
return range;
}
}
The class that is suppose to use the class I developed is:
public class CarTester
{
/**
* main() method
*/
public static void main(String[] args)
{
Car honda = new Car(30.0); // 30 miles per gallon
honda.addGas(9.0); // add 9 more gallons
honda.drive(210.0); // drive 210 miles
// print range remaining
System.out.println("Honda range remaining: " + honda.range());
Car toyota = new Car(26.0); // 26 miles per gallon
toyota.addGas(4.5); // add 4.5 more gallons
toyota.drive(150.0); // drive 150 miles
// print range remaining
System.out.println("Toyota range remaining: " + toyota.range());
}
}
Both classes compile successfully, however when the program is run I get the output "NaN," which stands for "Not a Number." I looked this up and supposedly it occurs when there is a mathematical process that attempts to divide by zero or something similar. I am not, I repeat, not looking for the answer, but a nudge in the right direction about where I might be making my mistake would be much appreciated (I'm sure it's a very small and stupid mistake). Thanks!

save your milesPerGallon variable at constructor:
public Car(double milesPerGallon)
{
this.milesPerGallon = milesPerGallon;
gas = 0.0;
}

milesPerGallon needs to be initialized to the constructor parameter.
Constructor:
public Car(double milesPerGallon)
{
this.milesPerGallon = milesPerGallon;
gas = 0.0;
}
milesPerGallon is used later but never initialized.

It seems as though you did not initialize milesPerGallon. The variable you accept in the constructor is different than the private variable you initialized at the top of your class. Typically people like to use something like public car(aMilesPerGallon) to make sure they know the difference. Or as the answer that was posted while I was typing says, this.milesPerGallon references the variable at the top of the class.

You aren't setting milesPerGallon in your constructor, thus it is initialized to 0.0. Are you dividing something by that variable somewhere?

You are not initializing milesPerGallon in your Car constructor. So it is taking 0.0 as default value. And when a number is divided by 0.0 you're getting NaN.

How to solve this program?

I found this Java exercise :
Create a class Sales that has TotalSales (double) , Commission (double),
Commissi onRate (double), and NoOfItems (integer).
write a java application that asks the user to enter the Total Sales and the number of items then calculates the commission and prints it out.
The commission rate should be as following:
Condition :
Less than 500, commissionRate is 0
Greater than or equal 500 or Number of Items >= 5, commission rate is 5%.
Grater than or equal 1000 or Number of items >=10, commission rate is 10%
..
I wrote this code:
Main Class :
import java.util.Scanner;
public class testSales {
public static void main(String[] args) {
Sales s1 = new Sales();
Scanner get = new Scanner(System.in);
System.out.println("Enter total Sales");
s1.totalSale = get.nextDouble();
System.out.println("Enter number of Items");
s1.NoOfItems = get.nextInt();
if(s1.totalSale < 500){
s1.commission = s1.commissionRate = 0;
}
else if(s1.totalSale >= 500 && s1.totalSale <= 999 || s1.NoOfItems >= 5 && s1.NoOfItems <=9){
s1.commission = s1.commissionRate = s1.totalSale * 5 / 100;
}else if(s1.totalSale >= 1000 || s1.NoOfItems >=10) {
s1.commission = s1.commissionRate = s1.totalSale *10/100;
}
System.out.println(s1.commission);
}
}

One problem in your code is the case where NoOfItems > 5 but totalSale < 500. For this case, the commission will incorrectly be set to 0 because the first if statement eats it.
Please try to be more specific with your question. "this doesn't work and I don't know why" is not easy to help with.

Aside from the point brought up by HedonicHedgehog, there are a few other things to consider:
The sales class only has two global variables, which corresponds to the information entered by the user. The other two fields, commission and commissionRate, are calculated values. Therefore, there is no need to create variables for them. Just add to the sales class accessor methods (getters) that return these values. For example, below is my getCommission() method:
public double getCommission()
{
return totalSales * getCommissionRate();
}
Of course, you can see this method is dependent upon the getCommissionRate() method. Because there is a gap on your requirements with total items, I am ignoring it for now:
public double getCommissionRate()
{
if (totalSales < 500)
return 0;
if(totalSales < 1000)
return .05;
else
return 0.1;
}
Alternatively, you could create a LOCAL commission variable, and set the value before returning it. It is a good programming practice to limit the scope of your variables. In this case, there is not a good reason to have a global commission or commissionRate variables.
Lastly, your test class is simplified because all you need to do is to prompt the user for the two needed fields, and it simply spits out the output because the Sales class provides the calculation needed to figure out the rest:
public static void main(String[] args)
{
Sales s1 = new Sales();
Scanner input = new Scanner(System.in);
System.out.print("Enter total Sales");
s1.setTotalSales(input.nextDouble());
System.out.print("Enter number of Items: ");
s1.setNumOfItems(input.nextInt());
System.out.printf("$%.2f", s1.getCommission());
input.close();
}
I used the printf() method to format the output string. The following is a sample run:
Enter total Sales: 503.45
Enter number of Items: 5
$25.17
Enter total Sales: 1003.67
Enter number of Items: 19
$100.37
Enter total Sales: 45.00
Enter number of Items: 19
$0.00
Remember that this example ignores the number of items because of the reasons already mentioned. Once you figure out what needs to be done to cover of the gap in the requirements, you can modify this code to do the rest. Also remember that your Sales class only requires two fields: totalSales and numOfItems. The other to components (commission, and commissionRate) are calculated; therefore, no global variable or setter methods needed. Just the two getter methods I provided.

Scanner and String Comparison

I have the following text in a file :
3
apple 4 1.00
chicken 1 3.25
cookie 38 0.25
avocado 1 4.00
blueberries 1 5.00
chicken 2 3.25
milk 9 4.50
tomato 27 0.50
chicken 2 3.25
I want to list each item and its number and its price but I want that if I encounter the same item again to add its number to the existing number I have
I figured out the first part but I can't get the second any one has any ideas ?
public static void main(String[] args) throws FileNotFoundException{
Scanner sc = new Scanner(new File("Groceries.txt"));
while(sc.hasNext()) {
String line=sc.nextLine();
Scanner ss = new Scanner(line);
if(ss.hasNextInt()) {
ss.next();
}
while(ss.hasNext()) {
String name=ss.next();
int number = readInt(ss);
double price = ss.nextDouble();
System.out.printf("The item is %s its number is %d and its price is %.1f\n",name,number,price);
}
}
}
public static int readInt(Scanner sc) {
while(!sc.hasNextInt()) {
sc.hasNext();
}
return sc.nextInt();
}

Create a container object like so:
public class Container
{
private String item;
private double cost;
...
}
Use a HashMap<Container, Double> as your data structure. Every time you come across a duplicate, update its value.
If there is a possibility for an arbitrary amount of repeats, you can use do the following:
public class ValueContainer
{
private int count;
private double value;
}
and have a HashMap<Container, ValueContainer>, and update accordingly. There seems to be some confusion between what you say in the question and in a comment. Regardless, with simple substitutions, this construct will get you to where you want to go.

Create a class describing the attributes of your item (name, price, quantity , count etc).
Create a list of items (Yes, use generics..) // u can also use a map instead of a list..
Now, with each line you read from the text file, first get the item name using split().
Check if the item is already present. If yes, take it out, increment its count and put it back. if No, then add a new item to the list.
Happy Coding...

Cannot use arrays or foreach loops to iterate over list of data and print out only certain values

The Prompt:
A program that accepts a candy name (for example, “chocolate-covered blueberries”), price per pound, and number of pounds sold in the average month, and displays the item’s data only if it is a best-selling item. Best-selling items are those that sell more than 2000 pounds per month.
b. A program that accepts candy data continuously until a sentinel value is entered and displays a list of high- priced, best-selling items. Best-selling items are defined in Exercise 2a. High-priced items are those that sell for $10 per pound or more.
Here is an example of a good design in operation:
High-priced, Best-selling Candy
Fudge $12.50 4500 lbs
Vanilla Creme $13.75 2200 lbs.
Fudge, 12.50, 4500 Jawbreakers, 6.50, 5500 Chocolate, 14.00, 790 Butterscotch, 9.50, 4500 Vanilla Creme, 13.75, 2200
Item that sold most pounds: Jawbreakers
but the problem I am having is that my teacher is not letting me use for loops, or arrays. And I do not want to define multiple instances of the same variable because it is finite to a certain amount.... What would be the most efficient way of doing this?
start
// Declarations
num QUIT = "Y";
final String HEADING = "High Priced, Best Selling Candy" + "\n" + "\n";
final String HSPS = candyName + " " + candyPrice + " " + candySold + " ";
final String MOSTSOLD = "Item that sold the most pounds is "
while <> QUIT;
enterCandy();
printHighPriceBestSelling();
printSoldMostPounds();
endwhile;
stop
entercandy()
String candyName = "poop";
double candyPrice = 0.0;
double candyWeight = 0.0;
int candySold = 0;
output "Please enter name of candy.";
input candyName;
output "Please enter candy price.";
input candyPrice;
output "Please enter pounds sold.";
input candySold;
printHighPriceBestSelling()
if(candySold > 2000 && candyPrice > 10)
{
output HEADING;
output HSPS;
}
else
{
output "There were/are no best selling, high priced candy!"
}
printSoldMostPounds();
//There is no basis for comparison.
There are only two ways of doing this. Create lots of different, artbitrary, and predefined variables to be filled by the loop until they are overwritten. Lets say 10. Or create an array. I am sure there is an overly complex way of doing it with nested if/switch/while loops, but why teach us/force us to use the ugly inefficient way?
output "MOSTSOLD ";

I'm assuming that, besides arrays, you're teacher isn't allowing you to use any standard Collection objects.
You could always just build your own LinkedList of entered candy orders--it's ugly, but it would work. A single "link" in the chain would look like this
public class CandyOrderLink {
private String candyName;
private Double candyPrice;
private Double orderAmount;
private CandyOrderLink nextOrderLink;
public CandyOrderLink(String candyName, Double candyPrice, Double orderAmount) {
this.candyName = candyName;
this.candyPrice = candyPrice;
this.orderAmount = orderAmount;
}
public CandyOrderLink getNextLink() {
return nextOrder;
}
public void setNextLink(CandyOrderLink nextOrderLink) {
this.nextOrderLink= nextOrderLink;
}
public String getCandyName() {
return candyName;
}
public Double getCandyPrice() {
return candyPrice;
}
public Double getOrderAmount() {
return orderAmount;
}
}
Not sure if I'm quite grasping the point of the assignment, but using a list data-structure to keep track of all orders will work. Just build a link for each entry (candyName, price, amount) and set that link as the next link of the previous one. At the end of input, iterate through the list by repeatedly calling getNextLink() on each link and printing information (if appropriate). Here is Wikipedia's article on linked lists: http://en.wikipedia.org/wiki/Linked_list

From the problem's description, I see no need to store the data entered so that it can be sorted. Both a and b state simple conditions for displaying a candy: greater than 2,000 pounds and at least $10/lb. You can print each entry immediately after it is entered.
However, your example output implies that you must pick the single best-selling candy which contradicts the description. Which is correct?

Java method passing/ordered logic inquiry

Let me first make it clear that this is for an assignment. I'm very new to programming so all guidance is greatly appreciated. The program I have to calculate is a parking fee charge for a $2.00 minimum for 3 hrs or less, .50 cents per additional hr, and charge is capped at $10/ per 24 hr period. Program must display most recent customer charge as well as running total. Constants must be initialized, Math.ceil must be used, and method calculateCharges must be used to solve each cust's charge. I get uber errors when I attempt to run this program, and you'll probably laugh when you see it, but where have I erred? I'm not looking for the answer to be handed to me, just looking for the logic behind how to get to the correctly written program. Please help!
package Parking;
import java.util.Scanner;
public class parking
{
private static final double THREE_HOURS = 2.00;
private static final double PER_HOUR_COST = .50;
private static final double WHOLE_DAY_COST = 10.00;
public static void main (String [] args)
{
double hoursParked = 0;
double cumulativeCharges = 0;
double storage1 = 0;
double storage2 = 0;
Scanner input = new Scanner(System.in);
System.out.print("\nThis program displays the charge for the most recent customer");
System.out.print(" as well as the running total of yesterday's receipts\n");
do
{ System.out.printf("Enter an number between 1-24 for hours parked in garage or -1 to quit:");
hoursParked = input.nextDouble ();
}
while((hoursParked > 0)&&(hoursParked <= 24)&&(hoursParked != -1));
if( hoursParked <= 3)
System.out.printf("Most recent customer's charge was: %.2f\n" , THREE_HOURS);
storage1 += THREE_HOURS;
if(hoursParked >= 18.01)
System.out.printf("Most recent customer's charge was:%.2f\n" , WHOLE_DAY_COST);
storage2 += WHOLE_DAY_COST;
double result = calculateCharges(hoursParked * PER_HOUR_COST);
System.out.printf("Most recent customer charge was:%.2f\n" , result);
cumulativeCharges = storage1 + storage2;
System.out.printf("Running total of yesterday's receipts is:%.2f\n" , cumulativeCharges);
} // end main
public static double calculateCharges (double hoursParked)
{
Math.ceil(hoursParked);
double total = hoursParked * PER_HOUR_COST;
return total;
} // end method calculateCharges
} // end class parking

In your while condition, the third condition is useless because if the value is positive, that necessarily means it is different than -1.
In your function you want to calculate the cost of parking time but you give as parameter a cost instead of a number of hours when you call your function. Is that normal? With that you will calculate the cost of the cost instead of the cost corresponding to a number of hours.
public static double calculateCharges (double hoursParked)
and
double result = calculateCharges(hoursParked * PER_HOUR_COST);

There's a couple things here.
Your while condition is checked at the end of the do loop, it is what allows you to break after reading hoursParked. Thus, the only way you are going to reach the code outside of the do loop (after the while), is if hoursParked is -1.
Secondly, when you do not have braces for your if conditions, you are only executing the first line after it, aka. the System.out.print's. Therefore, your first if condition will execute (printing the string), then storing 2.00 in storage1. Similarly, the second if condition will execute (printing the string), then storing 10.00 in storage2.
Because hoursParked is always -1, you are passing in (-1 * .5) to calculateCharges. You are not storing the result of Math.ceil() so it effectively does nothing. You are then returning (-.5 * .5) = -.25.
cumulativeCharges is just adding 2 + 10 in every case.
Suggestions - make sure you are encapsulating the code you want to execute inside the do loop, and only break after you have done your calculations on hoursParked.