Write a class that maintains the top ten scores for a game application, implemen

Question

Write a class that maintains the top ten scores for a game application, implementing the add and remove methods of Section 3.1.1, but using a singly linked list instead of an array.

public void add(GameEntry e) { 11 int newScore = e.getScore( ); 12 // is the new entry e really a high score? 13 if (numEntries < board.length || newScore > board[numEntries1].getScore( )) { 14 if (numEntries < board.length) // no score drops from the board 15 numEntries++; // so overall number increases 16 // shift any lower scores rightward to make room for the new entry 17 int j = numEntries 1; 18 while (j > 0 && board[j1].getScore( ) < newScore) { 19 board[j] = board[j1]; // shift entry from j-1 to j 20 j; // and decrement j 21 } 22 board[j] = e; // when done, add new entry 23 } 24 }

public GameEntry remove(int i) throws IndexOutOfBoundsException { 27 if (i < 0 || i >= numEntries) 28 throw new IndexOutOfBoundsException("Invalid index: " + i); 29 GameEntry temp = board[i]; // save the object to be removed 30 for (int j = i; j < numEntries 1; j++) // count up from i (not down) 31 board[j] = board[j+1]; // move one cell to the left 32 board[numEntries 1 ] = null; // null out the old last score 33 numEntries; 34 return temp; // return the removed object 35 }

Explanation / Answer

add and remove methods using a singly linked list:

public SLinkedList<GameEntry> add(GameEntry rank, SLinkedList<GameEntry> scores)
     {
         Node<GameEntry> currentNode = scores.getFirst();
         Node<GameEntry> nextNode = null;
         Node<GameEntry> previousNode = null;
         Node<GameEntry> newNode = new Node<GameEntry>();
         newNode.setElement(rank);

         if(scores.getSize() == 0)
         {
             scores.addFirst(newNode);
         }
         else
         {
             while(currentNode != null)
             {              
                 nextNode = currentNode.getNext();
                 if(nextNode == null)
                 {
                     scores.addLast(newNode);
                 }
                 else
                 {
                     scores.addAfter(currentNode, newNode);
                     break;
                 }              
             previousNode = currentNode;
             currentNode = currentNode.getNext();
             }
         }
         return scores;
     }

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