for (rows = 0; rows < bandstand.length; rows++){
     System.out.print ("Please enter number of positions in row " + (char)(rows + (int) 'A'));
     columns = keyboard.nextInt();
     bandstand[rows] = new double [columns];
     while ( columns < 0){
         System.out.print ("ERROR: Out of range, try again:");
         columns = keyboard.nextInt();
     }

 }

for (rows = 0; rows < bandstand.length; rows++){
    do {
        System.out.print ("Please enter number of positions in row " + (char)(rows + (int) 'A'));
        columns = keyboard.nextInt();
    } while (columns < 0);
    ...

for (rows = 0; rows < bandstand.length; rows++){
    System.out.print ("Please enter number of positions in row " + (char)(rows + (int) 'A'));
    columns = keyboard.nextInt();
    while (columns < 0) {
        System.out.print ("ERROR: Out of range, try again:");
        columns = keyboard.nextInt();
    }
    ...
    // note that array is created *after* columns is validated

for (rows = 0; rows < bandstand.length; rows++){
    System.out.print ("Please enter number of positions in row " + (char)(rows + (int) 'A'));
    columns = keyboard.nextInt();
    if (columns < 0) {
        System.out.println("Columns must be >= 0!");
        continue; // starts over for this row
    }
    ...

for (rows = 0; rows < bandstand.length; rows++){
     System.out.print ("Please enter number of positions in row " + (char)(rows + (int) 'A'));
     columns = keyboard.nextInt();
     while ( columns < 0){
         System.out.print ("ERROR: Out of range, try again:");
         columns = keyboard.nextInt();
     }
     bandstand[rows] = new double [columns];

 }

for (rows = 0; rows < bandstand.length; rows++){
 System.out.print ("Please enter number of positions in row " + (char)(rows + (int) 'A'));
 columns = keyboard.nextInt();
 if(columns >= 0) {
     bandstand[rows] = new double [columns];
  }
 while ( columns < 0){
     System.out.print ("ERROR: Out of range, try again:");
     columns = keyboard.nextInt();
 }

}
}