Thread: need help with homework program...thanks

Ok, I found the problem.

Time for a quick JAVA Basic Types Review:
In Java, there a 3 primary basic types (and a bunch of other ones for other things). Basic Type 1 is int. int is short of Integer. An integer is any whole number. Basic Type 2 is a double. A double is any number with decimal places. Basic Type 3 is String. A String is a word or phrase.

(Sorry for all the bolding but I wanted to highlight the important parts)

Now, this error:

at java.util.Scanner.nextInt(Unknown Source)

Is where the problem exists. But why is that a problem? Because you are inputting a number with decimal places. The method nextInt searches for the next integer, but it doesn't find one. Instead, you should be searching for the next double.

I would usually go more in-depth, but I don't know where to go from here. Tell me how much of this you understand.

i thought I did but apparently not because heres what i tried to change and got the same thing

 
import java.util.Scanner;
 
public class Assign4_Roberts{
	public static void main(String[] args){
 
		//enter shipping prices
		double ground = 0.00;
		double express = 5.00;
		double air = 15.00;
 
		//create a scanner
		Scanner in = new Scanner(System.in);
 
		System.out.println("Enter the item you are bidding on :");
		double answer =in.nextDouble(); 
 
		System.out.println("Enter your maximum bid: ");
		double num = in.nextDouble();
 
 
		System.out.println("Enter  desired  delivery  method ( 0 for ground four day, 1 for ground express, 2 for air shipping ) :");
		double shipping = in.nextDouble();
 
		if(shipping == 0)
			System.out.println("total:" + num + ground);
 
		if(shipping == 1)
			System.out.println("total:" + num + express);
 
		if(shipping == 2)
			System.out.println("total:" + num + air);
 
		//invoice
		System.out.println("Invoice :");
		System.out.println("Item :" + answer);
		System.out.println("Your Bid Price :" + num);
		System.out.println("Total :" + num + shipping);
 
 
	}
}[B][/B]

You have to deal with each input uniquely.

When you ask:

System.out.println("Enter the item you are bidding on :");

What basic type are you expecting to receive? Since you are expecting something like:

bicycle

you should be trying to get a String, not a double or an int.

When you ask:

System.out.println("Enter your maximum bid: ");

What basic type are you expecting to receive? Since you are expecting something like:

50.00

you should be trying to get a double.

When you ask:

System.out.println("Enter  desired  delivery  method ( 0 for ground four day, 1 for ground express, 2 for air shipping ) :");

What basic type are you expecting to receive? Since you are expecting something like:

1

you should be trying to get an int.

Tell me if you understand what I am saying. If you do understand, see if you can fix your code accordingly. I can tell you understand the basics of Scanner, but here is a recap of the method options for what you are attempting:
To get a String:
Scanner.nextLine() OR Scanner.next()
To get a double:
Scanner.nextDouble();
To get an int:
Scanner.nextInt();

Originally Posted by robertsbd

ok im in an entry level class and very new to java so your help would be greatly appreciated..here is what were supposed to do...

Write a program to take bids for an auction business. The program prompts the user to enter the name of item desired, next prompts the user to enter the bid price, next prompt the user to enter the desired method of shipping. There are three shipping methods available. ( 0 means ground shipping four day delivery, 1 means ground express two day delivery, 2 means air shipping one day delivery ). No charge for ground four day delivery, there is a $5.00 charge for ground express and $15.00 charge for air shipping ). Assume that the user of the program will be perfectly alert and a perfect typist, will not make any mental or typing mistakes.

A sample run would look like this :

Enter Item you are bidding on : bicycle
Enter your bid price : 50.00
Enter desired delivery method ( 0 for ground four day, 1 for ground express, 2 for air shipping ) : 1

Invoice :
Item : Bicycle
Your bid price : 50.00
shipping : 5.00
total : 55.00

here is my program so far...

import java.util.Scanner;
 
public class Assign4_Roberts{
	public static void main(String[] args){
 
		//enter shipping prices
		double ground = 0;
		double express = 5;
		double air = 15;
 
		//create a scanner
		Scanner input = new Scanner(System.in);
 
		System.out.println("Enter the item you are bidding on :");
		int answer =input.nextInt(); 
 
		System.out.println("Enter your maximum bid: ");
		int num = input.nextInt();
 
 
		System.out.println("Enter  desired  delivery  method ( 0 for ground four day, 1 for ground express, 2 for air shipping ) :");
		int shipping = input.nextInt();
 
		if(shipping == 0)
			System.out.println("total:" + num + ground);
 
		if(shipping == 1)
			System.out.println("total:" + num + express);
 
		if(shipping == 2)
			System.out.println("total:" + num + air);
 
		//invoice
		System.out.println("Invoice :");
		System.out.println("Item :" + answer);
		System.out.println("Your Bid Price :" + num);
		System.out.println("Total :" + num + shipping);
 
 
	}
}[B][/B]

and here is what happens when i try to run the program...im using eclipse btw

Enter the item you are bidding on :
bicycle
Exception in thread "main" java.util.InputMismatchException
at java.util.Scanner.throwFor(Unknown Source)
at java.util.Scanner.next(Unknown Source)
at java.util.Scanner.nextInt(Unknown Source)
at java.util.Scanner.nextInt(Unknown Source)
at Assign4_Roberts.main(Assign4_Roberts.java:20)


anybody know what im doing wrong

Input Mismatch Exception means you're entering the wrong type. It could be the user's fault, but in this case, it's not. You're want them to enter a String but the Scanner is scanning for an integer.

wouldn't bicycle be a String

as in

String answer = input.next();

I found another Input Mismatch Exception with num.

Also, shouldn't it be like this:

System.out.println("Enter your maximum bid: ");
		double num = input.nextDouble();

price has decimal points. An int doesn't.

Also, I've noticed another potential problem.

System.out.println("Enter your maximum bid: ");
		double num = input.nextDouble();

user enters -1000.00 since they want you to give them $1000.00.

That would make their total cost negative, and you end up giving out cash instead of receiving it.

Also, is shipping a constant, and if so, is it the same value no matter what the value of shipping is?

Oh, I see now, shipping is entered, but your println doesn't have:

System.out.println("Shipping:  $" + shipping);

Well, actually, you should have your if statements set shipping to the value of whatever shipping method the user chose.

Also, though you may not need to, should you have something in case they enter an int value outside the range?

Also, it could look better this way:

// near beginning of program, or wherever it won't throw a Null Pointer Exception, put this:
 
double total = 0.00; // creates a double and initializes it to 0.00.  
double shipping = 0.00; // this creates shipping, and initializes it to 0.00.  Creating it inside the while loop will cause the value in it to be lost after the loop ends, and causing your Invoice to throw a Null Pointer Exception.  
 
and then later 
boolean isValidShippingMethod = false; // creates a boolean that checks to see if the int value that the user enter is a match.  If not, it will ask them till they enter a valid one.  (Note, does not stop it if the user causes an Input Mismatch Exception.  
 
while (isAValidShippingMethod == false)
{
	System.out.println("Enter  desired  delivery  method ( 0 for ground four day, 1 for ground express, 2 for air shipping ) :");
		shipping = input.nextInt();
if (shipping == 0)
			{
shipping = ground;
total = num + ground;
System.out.println("total:" + total);
isAValidShippingMethod = true;  // this will stop the loop and not ask for a value again.  
		}
		else if (shipping == 1)
{
shipping = express;  
total = num + express;
			System.out.println("total:" + total);
isAValidShippingMethod = true;  // this will stop the loop and not ask for a value again.  
 
}
 
		else if (shipping == 2)
{
shipping = air;
total = num + air;
			System.out.println("total:" + total);
isAValidShippingMethod = true;  // this will stop the loop and not ask for a value again.  
}
 
else
{
System.out.println("Enter a valid shipping method.");
isAValidShippingMethod = false; // this will keep the while loop going till they enter a valid value
}
 
}  // end while

Originally Posted by aussiemcgr

You have to deal with each input uniquely.

When you ask:

System.out.println("Enter the item you are bidding on :");

What basic type are you expecting to receive? Since you are expecting something like:

you should be trying to get a String, not a double or an int.

When you ask:

System.out.println("Enter your maximum bid: ");

What basic type are you expecting to receive? Since you are expecting something like:

you should be trying to get a double.

When you ask:

System.out.println("Enter  desired  delivery  method ( 0 for ground four day, 1 for ground express, 2 for air shipping ) :");

What basic type are you expecting to receive? Since you are expecting something like:

you should be trying to get an int.

Tell me if you understand what I am saying. If you do understand, see if you can fix your code accordingly. I can tell you understand the basics of Scanner, but here is a recap of the method options for what you are attempting:
To get a String:
Scanner.nextLine() OR Scanner.next()
To get a double:
Scanner.nextDouble();
To get an int:
Scanner.nextInt();

Actually, it's the scanner reference variable I think he's using, not the class.

Also, something has been confusing me for a long time:

Is it valid to have

Scanner console = new Scanner(System.in);

in the main method, or does it have to be:

static Scanner console = new Scanner(System.in);

?

Won't it say:

non-static variable/method cannot be referenced from a static context if you do the first one, as the main method is static, and I thought a static method could only call other static methods. Maybe that's only the case for it's own static methods, not the static or non-static methods that you use another class to call.

Also, why does main have to be like this:

public static void main(String[] args)

?

Why an array of Strings? Why not a Vector or an ArrayList of Strings?

Also, what's to stop the programmer from creating two main methods?

Please don't hijack someone else's post...I will answer these questions here, but for future reference please start a new thread with questions beyond the scope of the original topic.

Originally Posted by javapenguin

Is it valid to have

Scanner console = new Scanner(System.in);

in the main method,

Yes it is valid. Having it outside allows access to the class from other methods - like any other variable it has a scope.

Originally Posted by javapenguin

Also, why does main have to be like this:

public static void main(String[] args)

?

Why an array of Strings? Why not a Vector or an ArrayList of Strings?

1) Vector or ArrayList requires an import, an array does not 2) these two objects didn't exist when java was being created and formed. 3) Maintains convention with other languages

Originally Posted by javapenguin

Also, what's to stop the programmer from creating two main methods?

In the same class you will receive a compile time error. You can have multiple mains in different classes of the same project, just need to specify which one to use to the JVM.

Originally Posted by copeg

Please don't hijack someone else's post...I will answer these questions here, but for future reference please start a new thread with questions beyond the scope of the original topic.



Yes it is valid. Having it outside allows access to the class from other methods - like any other variable it has a scope.



1) Vector or ArrayList requires an import, an array does not 2) these two objects didn't exist when java was being created and formed. 3) Maintains convention with other languages


In the same class you will receive a compile time error. You can have multiple mains in different classes of the same project, just need to specify which one to use to the JVM.

Ah, I found a moderator. I was trying to find the FAQ that told me what the titles with each user are and how many posts you need to get them:

How many do you need to get Java Kindergarten?

How many do you need to get Junior Member?

How many do you need to get Member?

How many do you need to get Senior Member?

How many do you need to get Elite Member?

How many do you need to get Senile Half Wit?

How many do you need to get Moderator?

How many do you need to get Super Moderator?

How many do you need to get Administrator?

Are there any other levels I'm not aware of?

Oh, and i think I answered the question of the creator of this thread anyway.

Originally Posted by javapenguin

Oh, and i think I answered the question of the creator of this thread anyway.

It doesn't matter, you are still hijacking his post. The question in your last post should be made into another thread. Try posting it in The Cafe since it is not program related.