|
need coding help
|
View this Thread in Original format
| stan229 |
any java coders? or c++ ?
this should be easy for you but im getting stumped.
(a) Create a Java class PositionPair, with instance fields private int firstOccurrence = -1 and private int secondOccurrence = -1. Use the Eclipse tool Source->Generate Getters and Setters to write the get and set methods for these fields.
(b) In your main class, write a method that contains an array PositionPair[] positions = new PositionPair[10]. Loop through all of digitArray. The first time you see the digit d in digitArray, store the index in positions[d].firstOccurrence and the second time, store the index in positions[d].secondOccurrence. When you are done, find the minimum value of all the firstOccurrences, that are positive, where the corresponding secondOccurrence is not -1. Return that minimum firstOccurrence as the return value of the method.
I cant get it working..
so far my code is
code:
package homework6;
public class PositionPair
{
private int firstOccurence = -1;
private int secondOccurence = -1;
public int getFirstOccurence()
{
return firstOccurence;
}
public void setFirstOccurence(int firstOccurence)
{
this.firstOccurence = firstOccurence;
}
public int getSecondOccurence()
{
return secondOccurence;
}
public void setSecondOccurence(int secondOccurence)
{
this.secondOccurence = secondOccurence;
}
public static int (int[] digitArray)
{
PositionPair[] positions = new PositionPair[10];
int i = 0;
int z = 0;
for (i = 0; i < digitArray.length; i++)
{
for (z = i + 1; z < digitArray.length; z++)
{
if (digitArray[z] == digitArray[i])
{
positions[i].firstOccurence = i;
positions[i].secondOccurence = z;
}
}
}
//return something
}
Thanks guys, really appreciate it |
|
|
| paranoik0 |
I found something odd:
| quote: | Originally posted by stan229
(b) In your main class, write a method that contains an array PositionPair[] positions = new PositionPair[10]. |
You were told to do this in your main class, not in the PositionPair class as it is. It seems odd to create an array of PositionPairs in a method part of a single PositionPair object. :wtf:
Also, shouldn't this part:
code:
if (digitArray[z] == digitArray[i])
actually be this:
code:
if (digitArray[z] == i)
:conf:
I think that's the problem with filling out the "positions" array, after it has been filled it should be easy to return the wanted value.
Try drawing a bunch of arrays in a sheet of paper and filling them out by yourself as you simulate the program running in your head. I ocasionally do that and it helps. Or you could just debug. |
|
|
| stan229 |
then i woudlnt be able to access firstOccurence cuz its private
unless theres another way?
also changin the thing to digitArray[z] == i doesn change anything, and im using that just to test if the value is repeated
the error i get is:
code:
Exception in thread "main" java.lang.NullPointerException
at homework6.PositionPair.(PositionPair.java:41)
at homework6.PositionPair.main(PositionPair.java:56)
|
|
|
| paranoik0 |
| quote: | Originally posted by stan229
then i woudlnt be able to access firstOccurence cuz its private
unless theres another way? |
That's why they tell you to generate the getFirstOccurence(), getSecondOccurence(), etc methods - you can use them to access the fields indirectly.
| quote: | also changin the thing to digitArray[z] == i doesn change anything, and im using that just to test if the value is repeated
the error i get is:
code:
Exception in thread "main" java.lang.NullPointerException
at homework6.PositionPair.(PositionPair.java:41)
at homework6.PositionPair.main(PositionPair.java:56)
|
NullPointerException in Java? :wtf: Maybe one of your for cicles isn't ending for some reason. |
|
|
| stan229 |
yea so i modified the code.. had to create a ne class
i used your advice on the method so i have
code:
int[] digitArray =
{ 0, 1, 1, 3, 4, 5, 5, 7, 8, 9 };
PositionPair[] positions = new PositionPair[10];
for (int i = 0; i < digitArray.length; i++)
{
for (int z = i + 1; z < digitArray.length; z++)
{
if (digitArray[z] == digitArray[i])
{
positions[i].setFirstOccurence(i);
positions[i].setSecondOccurence(z);
System.out.println(i);
System.out.println(z);
}
}
}
the prof juts sent us an email with the advice, but im ont sure if it even relates to me yet
| quote: |
To deal with the problem indicated below, we either have to initialize the array OR
check for null before accessing a particular location. I will expalin the former
solution in the assignment, right now.
Problem:
When checking to see if firstOccurrence equals -1 i
write "if(positions[num].getFirstOccurrence()==-1)" and when i run the
program it gives me a null pointer exception.
|
im confused lol
still getting a null pointer exception on the line that uses the setFirstOccurence method |
|
|
| stan229 |
tried a simple test and still got a nullPointerException..hmm
code:
positions[0].setFirstOccurence(5);
System.out.println(positions[0].getFirstOccurence());
the first line caused the exception.. wtf is going on lol |
|
|
| Omega_M |
| we don't do other people's homeworks. |
|
|
| ô§§|E |
Firstly, where's your default constructor for the PositionPair Class? cause at the moment you cant even create one of these objects right? So make one of those.
code:
public PostionPair()
{
firstOccurence = -1;
secondOccurence = -1;
}
Ur missing one lil concept here i think, the line ....
code:
PositionPair[] positions = new PositionPair[10];
Doesn't magically give you instantiations of 10 PositionPair objects, you still need to do this via ...
code:
for(int a = 0; a < 10; a++)
{
positions[a] = new PositionPair(); //You'll need a default constructor for this!
}
so now ur code looks like ....
code:
int[] digitArray = { 0, 1, 1, 3, 4, 5, 5, 7, 8, 9 };
PositionPair[] positions = new PositionPair[10];
//ADDED CODE
for(int a = 0; a < 10; a++)
{
positions[a] = new PositionPair(); //You'll need a default constructor for this!
}
for (int i = 0; i < digitArray.length; i++)
{
for (int z = i + 1; z < digitArray.length; z++)
{
if (digitArray[z] == digitArray[i])
{
positions[i].setFirstOccurence(i);
positions[i].setSecondOccurence(z);
System.out.println(i);
System.out.println(z);
}
}
}
Should do the trick by initialising the objects in the array first, let me know how that works for you |
|
|
| ô§§|E |
| wow u must of needed that badly :rolleyes: |
|
|
| stan229 |
thanks for everyones help i appreciate it.. lol i did
heres the final working code: :)
code:
// Sorry that I put everything in the test class.
//I realized to change it in the last minute and don't have time to, code will still work though.
package homework6;
public class PositionTest
{
/**
* Find the minimum index for firstOccurence
*
* @param positions
* @return index
*/
public static int findMinimum(PositionPair[] positions)
{
if (positions.length == 0)
return -1;
int smallestVal = -1;
for (int i = 0; i < positions.length; i++)
{
if (positions[i].getSecondOccurence() != -1
&& (positions[i].getFirstOccurence() < smallestVal || smallestVal == -1))
smallestVal = positions[i].getFirstOccurence();
}
return smallestVal;
}
public static void main(String[] args)
{
int[] digitArray =
{ 0, 1, 2, 1, 2, 5, 5, 7, 8, 9 };
PositionPair[] positions = new PositionPair[10];
for (int i = 0; i < positions.length; i++)
positions[i] = new PositionPair();
// Loop to test for firstOccurence and secondOccurence
for (int i = 0; i < digitArray.length; i++)
{
if (positions[digitArray[i]].getFirstOccurence() == -1)
{
positions[digitArray[i]].setFirstOccurence(i);
} else if (positions[digitArray[i]].getSecondOccurence() == -1)
{
positions[digitArray[i]].setSecondOccurence(i);
}
}
// Prints out array
for (int i = 0; i < positions.length; i++)
{
System.out.println(positions[i].getFirstOccurence() + " "
+ positions[i].getSecondOccurence());
}
int n = findMinimum(positions);
System.out.println(n);
}
}
code:
package homework6;
public class PositionPair
{
private int firstOccurence = -1;
private int secondOccurence = -1;
public int getFirstOccurence()
{
return firstOccurence;
}
public void setFirstOccurence(int firstOccurence)
{
this.firstOccurence = firstOccurence;
}
public int getSecondOccurence()
{
return secondOccurence;
}
public void setSecondOccurence(int secondOccurence)
{
this.secondOccurence = secondOccurence;
}
}
Once again, thank you guys. I was up till very late in the morning working on this that day. |
|
|
|
|
