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copied!<p>I think the problem is the swap itself: you forgot to set the tail.</p> <p>Here is a small test for exactly that problem:</p> <pre><code>@Test public void test() { SwapListImpl<String> list = new SwapListImpl<String>(); list.add("A"); list.add("B"); list.add("C"); list.swap("A", "C"); assertEquals("C", list.get(0)); assertEquals("C", list.getHead().val); assertEquals("B", list.get(1)); assertEquals("A", list.get(2)); assertEquals("A", list.getTail().val); list.add("D"); assertEquals("C", list.get(0)); assertEquals("C", list.getHead().val); assertEquals("B", list.get(1)); assertEquals("A", list.get(2)); assertEquals("D", list.get(3)); assertEquals("D", list.getTail().val); list.swap("A", "C"); assertEquals("A", list.get(0)); assertEquals("A", list.getHead().val); assertEquals("B", list.get(1)); assertEquals("C", list.get(2)); assertEquals("D", list.get(3)); assertEquals("D", list.getTail().val); list.swap("C", "B"); assertEquals("A", list.get(0)); assertEquals("A", list.getHead().val); assertEquals("C", list.get(1)); assertEquals("B", list.get(2)); assertEquals("D", list.get(3)); assertEquals("D", list.getTail().val); } </code></pre> <p>You see I added two methods to the list, for getting the head and tail, but that's not important - the test would even fail without the explicit test for head and tail. The extra methods for the list are really simple:</p> <pre><code> public Node<T> getTail() { return this.tail; } public Node<T> getHead() { return this.head; } </code></pre> <p>The problem of not setting tail occurs when swapping the last element of the list and then adding another element.</p> <p>Here is a fixed version of the actual swap:</p> <pre><code> if (foundFirst && foundSecond) { if (second == this.tail) { this.tail = first; } else if (first == this.tail) { this.tail = second; } if (first == this.head) { this.head = second; } else if (second == this.head) { this.head = first; } if (firstPrev == second) { first.next = second; } else { if (firstPrev != null) { firstPrev.next = second; } first.next = secondNext; } if (secondPrev == first) { second.next = first; } else { if (secondPrev != first && secondPrev != null) { secondPrev.next = first; } second.next = firstNext; } break; } </code></pre> <p>You see I didn't add lines to your code - instead I wrote the code in another way. I think it's more readable, but you also can try just to set the tail in the correct way. But it was too complex for me, so I reduced the complexity of that code - that's the reason why I rewrote it.</p> <p>I would suggest, that you use first and second for the first/second occurence and not for the first/second argument. I think that would improve the readability of the method. But that's another point ;-)</p> <p>Hope that helps - so the order IMHO is not the problem, but the tail.</p>

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