java - while循环中的条件不起作用？

private void Scan(DoublyLinkedList dList) { // T(n) = O(n)
    DNode p1 = dList.getFirst();

    while (p1 != null) {
        DNode p2 = p1.next;
        System.out.println(p1.getElement().toString()); // <--- Here it throws NullPointerException.

        if (p2.next != null) {
            DNode p3 = p2.next;

            if (p3.getElement() != null) {
                boolean b = Determinate.isPointRightSide(p1.getElement(), p2.getElement(),p3.getElement());

                if (b == true) {
                    p1 = p1.next;
                } else {
                    p1.next = p3;
                    p3.prev = p1;
                    dList.remove(p2);
                    p1 = p1.prev;
                }
            } else break;
        }else break;
    }
}

例外：

run:
Exception in thread "main" java.lang.NullPointerException
X :8.0  Y: 9.0angle0.0lol
        at ConvexHull.GrahamVersion.Scan(GrahamVersion.java:102)
        at ConvexHull.GrahamVersion.grahamScan(GrahamVersion.java:83)
        at ConvexHull.GrahamVersion.<init>(GrahamVersion.java:25)

它在NullPointerException上抛出System.out.println(p1.getElement().toString());。这意味着它不注意while循环的条件吗？

最佳答案

p1不是null，但是p1.getElement()返回了null。

删除toString()呼叫。您在sysout中不需要它。然后它将仅将null打印为“ null”。

关于java - while循环中的条件不起作用？，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/4290204/