Bubblesort

[NoviceJava]

hello,

I am having trouble with a program. It seems easy, but for some reason I am just not getting it. I need to create an array of random numbers and call a bubblesort method that I create myself. I then need to print the sorted array. I created the random array but I cant seem to figure out the sort method, which needs to follow in descending order. This is what I have:

 public static int[] sorting(int vals[])
  {
   int i,j;
   int max[] = new int [vals.length];
 
   System.arraycopy(vals,0,max,0,vals.length);
 
   for (i = 1; i < vals.length; i++)
      {
       for (j = 1; j < max.length; j++)
         {
           if (vals[j-1] > vals[j])
            {
             max[j-1] = vals[j];
             max[j] = vals[j-1];
            }
         }
      }
  return max;
 }
}

The message I am getting is the random numbers (the number of numbers is defined by the user and i printed the numbers just to see if it worked) along with the message [I@1eed786.

Please help,
Thanks

[JosAH]

You have two problems:

1) You are trying to print an array and get this: [I@1eed786; that's Java's way of
printing arrays: [ == array, I == int ,1ee786 == the hash code of the array. If you
want to print the contents of an array read the API documentation of the Arrays class.

2) Your bubble sort algorithm is like a Swedish Nilfisk vacuum cleaner: it s*cks
big times: it starts off nice by making a copy of the array but then you should
use *only* the copy for the comparisons and swaps.

kind regards,

Jos

[hsn]

i woul prefer if you post the hole code so i can test it.
i am not sure, but i think there is something with the sort algorithm (not sure). the i loop is good but with the j loop why dont you start with the last index of the array and go backward. it would be ;better.
please post the hole code so i can test it.

P.S. PLEASE USE THE CODE TAGS

hsn

[hsn]

a tip to save time. in the i loop and the j loop you are calling the length of the array in every time it loops. it is better to store the size in a variable and use the variable in the loop. you wont feel the difference. but trust me it matters.

good luck

hsn

[NoviceJava]

[HTML]
import java.io.*;

public class Bubble
{
public static void main(String[] args)
throws java.io.IOException
{
String s1, convert;
int i, num;

InputStreamReader isr = new InputStreamReader(System.in);

BufferedReader br = new BufferedReader(isr);

do
{
System.out.print("How many random numbers? ");

s1 = br.readLine();

num = Integer.parseInt(s1);

if (num > 9999 || num < 0)
System.out.println("Not valid.\n");
}
while(num > 9999 || num < 0);

System.out.println();

int mkrand[] = new int [num];

for(i = 0; i < num; i++)
{
mkrand[i] = 1 + (int)(Math.random()* 101);
System.out.print(mkrand[i] + " ");
}
System.out.print(sort(mkrand));

}
public static int[] sort(int vals[])
{
int i,j;
int max[] = new int [vals.length];

System.arraycopy(vals,0,max,0,vals.length);

for (i = 1; i < vals.length; i++)
{
for (j = 1; j < max.length; j++)
{
if (vals[j-1] > vals[j])
{
max[j-1] = vals[j];
max[j] = vals[j-1];
}
}
}
return max;
}
}[/HTML]


Here it is

[NoviceJava]

You have two problems:

1) You are trying to print an array and get this: [I@1eed786; that's Java's way of
printing arrays: [ == array, I == int ,1ee786 == the hash code of the array. If you
want to print the contents of an array read the API documentation of the Arrays class.

2) Your bubble sort algorithm is like a Swedish Nilfisk vacuum cleaner: it s*cks
big times: it starts off nice by making a copy of the array but then you should
use *only* the copy for the comparisons and swaps.

kind regards,

Jos

I am not sure what you mean by API documentation. As you may tell, I'm pretty new to this stuff.

[JosAH]

I am not sure what you mean by API documentation. As you may tell, I'm pretty new to this stuff.

API == Application Program Interface; the docs describe all the classes and their
methods that come with your Java distribution. You should use them whereever
you can and not reinvent the wheel. Here's a link.

kind regards,

Jos

[hsn]

i am shocked that you don't know about the API. it is the first thing i have learned in java. sownload it, it will help you alot..


hsn

[NoviceJava]

i am shocked that you don't know about the API. it is the first thing i have learned in java. sownload it, it will help you alot..


hsn

Ok, I'm on it. But did you see any thing else wrong with my code?

[hsn]

hello m8.
as Jos said your bubble sort algorithm ******. it is not correct for
88 23 70 6 it gave me
23 88 6 70
you should do some reading about this algorithm and understand it well. do some search and you will understand it it is one of the simplest algorithms.
and you can't say

System.out.print(sort(mkrand));

you have to go in a loop to print the array.

Good luck

hsn

[JosAH]

you have to go in a loop to print the array.

No he doesn't; that's what me fIrst remark was about (see my first reply).
He could simply do this:

System.out.println(Arrays.toString(hisArray));
 

kind regards,

Jos

[hsn]

No he doesn't; that's what me fIrst remark was about (see my first reply).
He could simply do this:

System.out.println(Arrays.toString(hisArray));
 

kind regards,

Jos

sorry m8 i didn't see that one

[NoviceJava]

sorry m8 i didn't see that one

I tried this:

System.out.println(Arrays.toString(sorting(mkrand) ))

but I got the error message saying that it cannot find symbol
symbol: variable Arrays

[NoviceJava]

I tried this:

System.out.println(Arrays.toString(sorting(mkrand) ))

but I got the error message saying that it cannot find symbol
symbol: variable Arrays

Oh, I also created a new a new selection sort method:
[HTML]
public static int[] sorting(int vals[])
{
for (int i = 0; i < vals.length; i++)
{
int index = i;
for (int j = i+1; j < vals.length; j++)
if (vals[j] > vals[index])
index = j;

int largerNumber = vals[index];
vals[index] = vals[i];
vals[i] = largerNumber;
}
return vals;
}[/HTML]

Can you tell me if this will give me the desired results? I still can't figure out how to print the array. I tried what was suggested but it still did not work.

[JosAH]

I still can't figure out how to print the array. I tried what was suggested but it still did not work.

You have to import that class, just like every class not in the package java.lang.
This is how you do that: before you define any class add the line:

java.util.Arrays;
 

How did I know what package this Arrrays class is in? By reading the API docs.

kind regards,

Jos

[NoviceJava]

You have to import that class, just like every class not in the package java.lang.
This is how you do that: before you define any class add the line:

java.util.Arrays;
 

How did I know what package this Arrrays class is in? By reading the API docs.

kind regards,

Jos

Thanks.

I did read it but I never found the part about converting to a String.

[JosAH]

Thanks.

I did read it but I never found the part about converting to a String.

But in reply #13 you wrote:

I tried this:

System.out.println(Arrays.toString(sorting(mkrand) ))

but I got the error message saying that it cannot find symbol
symbol: variable Arrays

That simply indicates that the compiler couldn't find the 'Arrays' symbol, i.e. it
couldn't check whether or not there even *was* a method named toString(). That
should've fired up your attention: when a class symbol can't be found you either
misspelt its name or you have forgotten to import it.

kind regards,

Jos