T3

Here is a simple class implementing a sorted list of integers. The list is sorted in ascending order. It has a method to insert an element, and a method to retrieve the greatest element from the list.

package Examples; import java.util.LinkedList; // Sorted list of integers; in ascending order. public class SimpleIntSortedList { private LinkedList s; private Integer max; public SimpleIntSortedList() { s = new LinkedList(); } public void insert(Integer x) { assert x!=null : "PRE"; int i = 0; for (Integer y : s) { if (y > x) break; i++; } s.add(i, x); // bug: should be x > max if (max == null || x < max) max = x; } // Retrieve the greatest element from the list, if it is not empty. public Integer get() { assert !s.isEmpty() : "PRE"; Integer x = max; s.remove(max); if (s.isEmpty()) max = null ; else max = s.getLast() ; assert s.isEmpty() || x >= s.getLast() : "POST"; return x; } // a class invariant private boolean classinv__() { return s.isEmpty() || s.contains(max); } }