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# Uni JAVA Exam Monday HELP!!

Shannon Pink
Greenhorn
Posts: 6
hey guys, im pretty new to this forum I have only posted once, I tend to spectate more than participate. I'm a first year Computing and Multimedia student at an Australian University and on this monday I will be sitting my first java exam which is worth 60% of my grade so I want to do really well. I have studied very hard and now there are only a couple of concepts that I don't understand and I was hopeing some of you guys could help me out.
The first concept is the selection sort algorithm.
I will try and explain my understanding of it.
Selection sort scans te entire list (int array) and determines the smallest value, this value is then swapped with the value in the first value. Now it scans the list again except for the first value and swaps the next smallest value with the one in the second position. The process continues untill the list is in order.
okay here is an example:
Selection sort example / tutorial
LOL hahaha I understand it now =D don't worry about that one.
Ok now the only concept in my exam I don't understand properlly is Two - Diamentional Arrays
coult someone plz go through them with me or give me a link to some good teachings?

Shannon Pink
Greenhorn
Posts: 6
ok here is an example out of my study guide:
int [ ] [ ] a = { {0, 2, 4, 5, 8},
{10, 1, 3, 6, 9},
{1, 4, 6, 4, 3} };
/*I am really lost when it comes to this, I mean which lot of numbers are stored in the first dimention and which are stored in the second? */
final int ROWS = a.length;
final int COLUMNS = a[0].length;
/*what values are ROWS and COLUMNS assigned? */
int x;
for (int i = 0; i < ROWS; i++)
{
x = a [i] [0];
//again I don't get this

for (int j = 0; j < COLUMNS ; j++)
{
if (a [i] [j] > x)
x = a [i] [j];
}
System.out.println( i + "\t" + x);
}
Could someone please explain all this to me bcause I don't undestant it at all.
What would the output of this code be?
and what would be the value of ROWS and COLUMNS be?

Amy Phillips
Ranch Hand
Posts: 280
Dingo,
The best way to learn java is to write java, you have plenty of code examples so why not actually try running them and seeing what the results are?
I think this would help you far more than if we just told you
Good luck with the exam

David O'Meara
Rancher
Posts: 13459
"DINGO",
Howdy from Perth, but unfortunately your display name is invalid, and accounts with invalid display names get deleted.
Have a look at the naming rules then edit your profile to fix your display name.
Ta,
Dave
[ Oops, typo ]
[ June 27, 2003: Message edited by: David O'Meara ]

Shannon Pink
Greenhorn
Posts: 6
Hi Amy! I see your point and I agree when it comes to some concepts but I do not understand what is going on in this case at all so I would really appeciate if someone could explain to me what is happening in each line. Thanks for your luck though

Francis Siu
Ranch Hand
Posts: 867
Shannon Pink
Many ranchers can answer you question,after you take action.

Shannon Pink
Greenhorn
Posts: 6
what dude?! I did take action Shannon Pink is my real name! I originally had it dingo... thanks for the help people.... pfffft!

Ranch Hand
Posts: 116
Hi Shanon,
The idea of 2D Array is similar to how the normal human eye processes the text or data we see in the forms of lines. The idea is.. see when your reading this message of mine the human brain processes the text from the left to the right side and line by line... similarly we need to simulate the process to the language processor what ever language it might be.. Thus when u declare a 2D array the first dimension points at the row no(horizontal cordinate) of the data say and the second dimension points to the column no(vertical cordinate) and this is how the data found at the intersection of both these dimensions is found. Hope I made myself clear. Any further assistance would be my previlege.
All the best,
Gaya3
------------------------------------------------
Beginning is half done

Joe Brennan
Greenhorn
Posts: 9
Hi Shannon
Hope your exam went well !
Joe

Shannon Pink
Greenhorn
Posts: 6
thanks for the help Gayathri, I understand that concept now
I think I did really well in the exam there was only one question that I didn't really know how to answer.
cyas later

Thomas Thomas
Greenhorn
Posts: 28
Hi
Let me try to explain the concept of two dimensional arrays .
when u say int[][] a;
the reference variable 'a' is refering to an
int[][] array object;
Inorder to define the variable 'a' u have to say
a= new int[3][];
The point is JVM needs to know only the size of the object assigned to the variable a.
this will inturn create 3 int[] array object.
each holding there reference variable in a0],
a[1],a[2]. so from here onwards visualize it as reference variable for single dimensional arrrays.
the following code r perfectly OK.
a[0]= new int [5];
a[1]= new int [100];
as u know a[2] will be having a default null value.
so don't think that a two dimensional array will be 2*2 matrix..