Array and GUI

[Bryan Peach]

hey there... I am trying to test this program before i start trying to incorporate the GUI stuff. I am new to this stuff and I seem to be getting a type casting error. Can someone take a look and let me know what you think?

    
import java.util.Scanner; 
public class Apartment {
    	int aptnum; //Apartment number
    	int occ; //number of occupants in apartment
    	int people; //number of people in building
    	double avgocc; // average occupants per apartment
    	int abv; //number of apartments above average
    	int bel; // number of apartments below average
    	int index;//index counter variable
    	Scanner in;
    	int apartment[] = new int[9];
    	
    //methods
    
    public void readData()//reads and stores data into the array
    {
    	System.out.println("Please enter the number of occupants in apartment #1");
    	for(int index = 0; index<apartment.length;index++)
    		apartment[index]=in.nextInt();
    		System.out.println("Please enter the number of occupants in apartment # " + (index+1));
    }
    
    public int addNumPeople()// returns total number of people in building
    {
    	people = 0;
    	for (int aptNo = 0; aptNo < apartment.length; aptNo++)
    		people=people+apartment[aptNo];
    		return people;
    }
    
    public int getAverage()//returns average occupants per apartment
    {
    	avgocc=double(people/10);
    	return avgocc;
    }
    
    public int getAboveAverage()//returns number of apartments containing about average occupants
    {
    	abv=0;
    	for(int index = avgocc; index<9;index++)
    		abv=abv+apartment[index];
    		return abv;
    }
    
    public int getBelowAverage()// calculates number of apartments with below average occupants
    {
    	bel = 0;
    	for(int index = 0; index<avgocc;index++)
    		bel=bel+apartment[index];
    		return bel;
    }
    
    
    	
    
    public static void main(String[] args) {
    	
    	Scanner in = new Scanner(System.in);
    	
    	Apartment someApartment=new Apartment();
    	
    	someApartment.readData();
    	someApartment.addNumPeople();
    	someApartment.getAverage();
    	someApartment.getAboveAverage();
    	someApartment.getBelowAverage();
    	
    	System.out.println("The total number of people in the building is: " +people);
    	System.out.println("The Average number of people in each apartment is: " +avgocc);
    	System.out.println("The number of apartments with above average occupants is: " +abv);
    	System.out.println("The number of apartments with below average occupants is: " +bel);
    	
    	
    	
    }
}

If you have not figured it out.. the array is suposed to represent a apartment building with each element of the array representing individual apartments. We are supose to read data into the array and then perform the different operations as seen in my methods... the type cast error is get is in the getAverage method. I've tried to cast it as an int and as a double and neither way will work...

[Bryan Peach]

ok forget about the tyoe casting i got that figureed out... but now when i go to compile i get a null pointer exception in the main method somewhere... does anyone know how to remedy that?

[Mark Vedder]

Your getAverage method is declared to return an int. However, the math you perform results in a double, which is a floating point number. You want to assign that calculation to avgocc, which is a double. So that's fine. However, you cannot use avgocc as the return value since it is a double and your method is declared to return an int. So you either need to cast it to an int (option 1) and lose precision (2 vs 2.4) before you return it, or your method needs to be declared to return a double rather than an int (option 2).

 
//Option 1, in which you will lose precision
public int getAverage()//returns average occupants per apartment
{
    avgocc = people / 10;
    return (int) avgocc;
}

//Option 2, precision is maintained by having method return a double rather than an int
public double getAverage()//returns average occupants per apartment
{
    avgocc = people / 10;
    return avgocc;
}

Since your avgocc variable is a double, and since it makes more sense that an average be a floating number (unless your requirements say otherwise) I think option two is the better one.

You have some other issues looming. I'll comment on them in a another post.

[Mark Vedder]

Bryan Peach wrote:ok forget about the tyoe casting i got that figureed out... but now when i go to compile i get a null pointer exception in the main method somewhere... does anyone know how to remedy that?

Can you post the entire exception you are getting, along with your new code. I can then teach you how to read an exception stack trace so you can answer your question yourself. A much more valuable outcome.

[Bryan Peach]

i got the excepction... it was because i was declaring my Scanner in object in the main... and it was looking for it in my read data method... all i did was move the declaration into the method and it worked.... however in my loop for readData I want it to get the nextInt.. and then prompt me to eneter the value for the next apartment number... but it is not going that... my results are this..

Please enter the number of occupants in apartment #1
1
2
3
4
5
6
7
8
9
Please enter the number of occupants in apartment # 1
The total number of people in the building is: 45
The Average number of people in each apartment is: 4
The number of apartments with above average occupants is: 35
The number of apartments with below average occupants is: 10

there is also something seriously wrong with my above and below average methods that i need to figure out

[Bryan Peach]

ok so i'm trying to solve my above average method and i wrote it like this:

    
 public int getAboveAverage()//returns number of apartments containing above average occupants
    {
    	abv=0;
    	for(int i=0; i<9;index++)
    		if(apartment[index]>avgocc)
    		{
    			abv++;
    		}
    		return abv;
    }

but it is giving me this error:

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 10
at Apartment.getAboveAverage(Apartment.java:51)
at Apartment.main(Apartment.java:78)

but i don't get it because my array has 10 spots so my loop should only check up until 9 right? why is it giving me this error?

[Bryan Peach]

I'll post my code again since there have been some changes since i orginally did so

    
import java.util.Scanner; 
public class Apartment {
    	int aptnum; //Apartment number
    	int occ; //number of occupants in apartment
    	static int people; //number of people in building
    	static int avgocc; // average occupants per apartment
    	static int abv; //number of apartments above average
    	static int bel; // number of apartments below average
    	int index;//index counter variable
    	Scanner in;
    	int apartment[] = new int[10];
    	
    //methods
    
    public void readData()//reads and stores data into the array
    {
    	Scanner in = new Scanner(System.in);
    	System.out.println("Please enter the number of occupants in apartment #1");
    	for(int index = 0; index<apartment.length;index++)
    		apartment[index]=in.nextInt();
    		System.out.println("Please enter the number of occupants in apartment #" + index+1);
    }
    
    public int addNumPeople()// returns total number of people in building
    {
    	people = 0;
    	for (int aptNo = 0; aptNo < apartment.length; aptNo++)
    		people=people+apartment[aptNo];
    		return people;
    }
    
    public int getAverage()//returns average occupants per apartment
    {
    	avgocc=(people/10);
    	return avgocc;
    }
    
    public int getAboveAverage()//returns number of apartments containing above average occupants
    {
    	abv=0;
    	for(int i=0; i<=9;index++)
    		if(apartment[index]>avgocc)
    		{
    			abv++;
    		}
    		return abv;
    }
    
    public int getBelowAverage()// calculates number of apartments with below average occupants
    {
    	bel = 0;
    	for(int index = 0; index<avgocc;index++)
    		bel=bel+apartment[index];
    		return bel;
    }
    
    
    	
    
    public static void main(String[] args) {
    	
    	
    	
    	Apartment someApartment=new Apartment();
    	
    	someApartment.readData();
    	someApartment.addNumPeople();
    	someApartment.getAverage();
    	someApartment.getAboveAverage();
    	someApartment.getBelowAverage();
    	
    	System.out.println("The total number of people in the building is: " +people);
    	System.out.println("The Average number of people in each apartment is: " +avgocc);
    	System.out.println("The number of apartments with above average occupants is: " +abv);
    	System.out.println("The number of apartments with below average occupants is: " +bel);
    	
    	
    	
    }
}

[Sean Clark]

Well in the code you posted...

for(int i=0; i<=9;index++)   

you declare i in your for loop but then you are incrementing index...?
Change index and the line below to i instead.

Also although not important I would write the for loop as, more readable:

for(int i=0; i<10;i++) 

Sean

[pete stein]

Here's a classic "gotcha" that has gotten all of us at least once in our coding career:

    public void readData() {
    	Scanner in = new Scanner(System.in);
    	System.out.println("Please enter the number of occupants in apartment #1");
    	for(int index = 0; index<apartment.length;index++)
    		apartment[index]=in.nextInt();
    		System.out.println("Please enter the number of occupants in apartment #" + index+1);
    }

Your for loop here is not doing what you think it's doing, and this is partly due to indentation that is leading you astray. Because the for loop block is not enclosed in curly braces, it is only looping on the first line, on this statement:

apartment[index]=in.nextInt();

and the loop does not contain this statement:

System.out.println("Please enter the number of occupants in apartment #" + index+1);

The solution: always place all loops and if blocks within curly braces. For example:

   public void readData() {
      Scanner in = new Scanner(System.in);
      
      // note the curly braces!
      for (int index = 0; index < apartment.length; index++) {
         // better to call println within the loop and before reading in the number
         System.out.println("Please enter the number of occupants in apartment #" + (index + 1));
         apartment[index] = in.nextInt();
      }
   }

[Bryan Peach]

thanks for the pointers guys.. it seems like even pretty simple programming tasks get me very confused... the readData loop kind of works how i want it now but instead of geting 1,2,3,4 etc... it is giving me

Please enter the number of occupants in apartment #1
1
Please enter the number of occupants in apartment #0
2
Please enter the number of occupants in apartment #2
3
Please enter the number of occupants in apartment #4

4
Please enter the number of occupants in apartment #6
5

And I cannot for the life of me figure out this aboveaverage or below average thing.

    
 public int getAboveAverage()//returns number of apartments containing above average occupants
    {
    	abv=0;
    	for(int i=0; i<=9; i++)
    		if(apartment[index]>avgocc)
    		{
    			abv++;
    		}
    		return abv;
    }

i don't know what that gives me but its not the number of apartments with above average occupants... please help...

[Bryan Peach]

I figured the readData thing figured out but i could use some help on the above and below average methods