(Homework) Arrary Confusion

[Newjavabug]

I am supposed to be writing an array that shifts numbers to the right in BlueJ. For example 1, 2, 3, 4, 5 would be printed as 5, 1, 2, 3, 4. I have searched the Internet and cannot figure out how to begin with this. I did see one post on this site, but the conversation did not make sense to me.

Does anyone know where I can find information about starting to do this? How do you learn what code to use??? So far, below is my pathetic attempt to start:

public class Array_Shift
{
public static void main(String arg[])
{
int num[] = {1, 2, 3, 4, 5};
}
}

[JosAH]

I am supposed to be writing an array that shifts numbers to the right in BlueJ. For example 1, 2, 3, 4, 5 would be printed as 5, 1, 2, 3, 4. I have searched the Internet and cannot figure out how to begin with this. I did see one post on this site, but the conversation did not make sense to me.

Does anyone know where I can find information about starting to do this? How do you learn what code to use??? So far, below is my pathetic attempt to start:

[code=java]
public class Array_Shift
{
public static void main(String arg[])
{
int num[] = {1, 2, 3, 4, 5};
}
}[/code]

Because arrays are very static data structures you can't structurally manipulate
them, i.e you have to move the content of the elements around. You start with
this:
[code=java]
{ 1, 2, 3, 4, 5 }
[/code]
and you want the end result to be this:
[code=java]
{ 5, 1, 2, 3, 4 }
[/code]
If you look closely, you see that you have to move a[i] to a[i+1] for all applicable
values of i. the rightmost element must end up as the first element. Moving all
elements one position to the right can be done using a bit of loop trickery-dickery:
[code=java]
for (int i= array.length; --i > 0; array[i]= array[i-1]);
[/code]
This is a complete giveaway so figure it out yourself; all elements are moved to the
right starting on the right side of the array. This loop results in the following
content of the array:
[code=java]
{ 1, 1, 2, 3, 4 }
[/code]
So the rightmost element has to be saved temporarily before the loop statrts and
put back at the beginning of the array after the loop ends; I leave that to you.

kind regards,

Jos

[r035198x]

...
[code=java]
for (int i= array.length; --i > 0; array[i]= array[i-1]);
[/code]
....

That old bag again ...

[JosAH]

That old bag again ...

What you're staring at Sir, is a carefully handcrafted for loop with an empty body.
Nuffin' wrong with it.

kind regards,

Jos ;-)

[Newjavabug]

Thank you! I'm not entirely sure I understand what to do, but I'll work on it and let you know if my solution works later tonight.

[JosAH]

Thank you! I'm not entirely sure I understand what to do, but I'll work on it and let you know if my solution works later tonight.

Study that funny for-loop and write a few small test programs and see what it
does; r035198x doesn't like those terse tricky loops but don't pay any attention
to him ;-)

Basically all you have to do is this:

[code=java]
int temp= array[array.length-1]; // save the last element
... // that funny loop of mine here
array[0]= temp; // put last element in the first place
[/code]

Now that isn't rocket science is it?

kind regards,

Jos

[Newjavabug]

Agh, I'm sorry... I feel like this is rocket science. I've only done one java assignment, and it was in a lab, so I am still shakey on even starting the "public" stuff.

I tried a few more pathetic attempts, but the array variable isn't even recognized.

Could you give me full example? I need to learn how to construct this type of thing for the test, so I am by no means asking for an answer to my assignment. I think you've given me the answer already, but your responses are not registering with me for some reason (probably my ignorance on this topic). Perhaps, give me an example of a left rotate, and I can try to figure out the right one? I have no idea...


public class input_text
{
public static void main(String arg[])
{
int num[] = {1, 2, 3, 4, 5};
{
int temp= array[array.length-1];
for (int i= array.length; --i > 0; array[i]= array[i-1]);
array[0]= temp; // put last element in the first place
}
}
}

[JosAH]

The clue is that I'm using the generic name 'array' for the array. You named it 'num'
and declared it that way. Simply change my name to your name.

kind regards,

Jos

[Newjavabug]

Ahhh, thank you! ^_^