Non-static cannot be referenced from a static context - ?

Question

Hi, i understand (kinda) what the error means
i think its saying that i cannot call a non-static method "bubbleSort"
from the static method main (correct?)
but i dont know how to fix it...
do i make bubbleSort
public static void bubbleSort???
C:\jLotto\dataFile\SortNumbers.java:80: non-static method bubbleSort(int[]) cannot be referenced from a static context
          bubbleSort( a ); //sort the array into ascending numbers
my code:
import java.io.*;
import java.util.*;
public class SortNumbers
     public static void main( String args[]) throws IOException
      int num;
          int a[] = new int[7]; //an array for sorting numbers
          File inputFile = new File("C:\\jLotto\\dataFile\\outagain.txt");
          File outputFile = new File("C:\\jLotto\\dataFile\\sortedNum.txt");
        BufferedReader br = new BufferedReader( new FileReader( inputFile ));
      PrintWriter pw = new PrintWriter( new FileWriter( outputFile ));
      String line = br.readLine();
      while( line != null ){//reads a single line from the file
         StringBuffer buffer = new StringBuffer(31);          //create a buffer
         StringTokenizer st = new StringTokenizer( line," "); //create a tokenizer
         while (st.hasMoreTokens()){
                    // the first 4 tokens are id,month,day,ccyy, no sorting needed
                    // so they are simply moved into the buffer
                    for (int i =1; i<5; i++){
                         num = Integer.parseInt(st.nextToken());
                         buffer.append( num );
                         buffer.append( "|");
                    //tokens 5 to 11 need to be sorted into acending order
                    //so read tokens 5 to 11 into an array for sorting
                    for (int i =0; i<7; i++){
                         a[i] = Integer.parseInt(st.nextToken());
                 bubbleSort( a ); //sort the array into ascending numbers
                  //the array is sorted so read array back into the buffer
                  for ( int i = 0; i < a.length; i++ ){
                       buffer.append( a[ i ] );
                       buffer.append(  "|" ) ;
               }//end of while st.hasMoreTokens
         //then write out the record from the stringBuffer
         pw.println( buffer );
         line = br.readLine();
      }//end of while != null
          br.close();
          pw.close();
     }//end of static main
   // sort the elements of an array with bubble sort
   public void bubbleSort( int b[] )
      int swapMade = 0; //if after one pass, no swaps were made - exit
      for ( int pass = 1; pass < ( b.length - pass) ; pass++ ) // passes reduced for speed
          for ( int i = 0; i < b.length - 1; i++ ) // one pass
              if ( b[ i ] > b[ i + 1 ] )            // one comparison
                  swap( b, i, i + 1 );              // one swap
                  swapMade = 1;
              }  // end of if
           } //end of one pass
         if (swapMade == 0) pass = 7; //no swaps, so break out of outter for loop
      }//end of passes, end of outter for loop
   }//end of bubblesort method
   // swap two elements of an array
   public void swap( int c[], int first, int second )
      int hold;  // temporary holding area for swap
      hold = c[ first ];
      c[ first ] = c[ second ];
      c[ second ] = hold;
   }   //end of swap
}//end of class SortNumbers

Answer 1

Static means
when u run the program (a class), there is only one variabel / type in memory.
ex static int a; //assume it's inside the aStaticClass
mean no wonder how many u create object from this class, variabel a only have 1 in memory. so if u change a (ex a=1;) all instance of this aStaticClass will effected (because they share the same variabel).
Try to read more at :
http://java.sun.com/docs/books/tutorial/java/javaOO/classvars.html
I hope this will help you....happy new year
yonscun