我想使用合并排序来对我的双向链表进行排序。我创建了3个类（Node，DoublyLinkedList，MergeSort），但它会为这些行抛出此异常：
1.in the getNodes method of DoublyLinkedList---> throw new IndexOutOfBoundsException();
2.in the add method of DoublyLinkedList-----> Node cursor = getNodes(index);
3.in the sort method of MergeSort class------> listTwo.add(x,localDoublyLinkedList.getValue(x));
4.in the main method of DoublyLinkedList----->merge.sort();
这是我的Merge类:(我把这个类的整个代码放在了解beter中）
public class MergeSort {
private DoublyLinkedList localDoublyLinkedList;
public MergeSort(DoublyLinkedList list) {
localDoublyLinkedList = list;
}
public void sort() {
if (localDoublyLinkedList.size() <= 1) {
return;
}
DoublyLinkedList listOne = new DoublyLinkedList();
DoublyLinkedList listTwo = new DoublyLinkedList();
for (int x = 0; x < (localDoublyLinkedList.size() / 2); x++) {
listOne.add(x, localDoublyLinkedList.getValue(x));
}
for (int x = (localDoublyLinkedList.size() / 2) + 1; x < localDoublyLinkedList.size(); x++) {
listTwo.add(x, localDoublyLinkedList.getValue(x));
}
//Split the DoublyLinkedList again
MergeSort sort1 = new MergeSort(listOne);
MergeSort sort2 = new MergeSort(listTwo);
sort1.sort();
sort2.sort();
merge(listOne, listTwo);
}
public void merge(DoublyLinkedList a, DoublyLinkedList b) {
int x = 0;
int y = 0;
int z = 0;
while (x < a.size() && y < b.size()) {
if (a.getValue(x) < b.getValue(y)) {
localDoublyLinkedList.add(z, a.getValue(x));
x++;
} else {
localDoublyLinkedList.add(z, b.getValue(y));
y++;
}
z++;
}
//copy remaining elements to the tail of a[];
for (int i = x; i < a.size(); i++) {
localDoublyLinkedList.add(z, a.getValue(i));
z++;
}
for (int i = y; i < b.size(); i++) {
localDoublyLinkedList.add(z, b.getValue(i));
z++;
}
}
}
只是我的DoublyLinkedList的一部分：
private Node getNodes(int index) throws IndexOutOfBoundsException {
if (index < 0 || index > length) {
throw new IndexOutOfBoundsException();
} else {
Node cursor = head;
for (int i = 0; i < index; i++) {
cursor = cursor.getNext();
}
return cursor;
}
}
public void add(int index, int value) throws IndexOutOfBoundsException {
Node cursor = getNodes(index);
Node temp = new Node(value);
temp.setPrev(cursor);
temp.setNext(cursor.getNext());
cursor.getNext().setPrev(temp);
cursor.setNext(temp);
length++;
}
public static void main(String[] args) {
int i = 0;
i = getRandomNumber(10, 10000);
DoublyLinkedList list = new DoublyLinkedList();
for (int j = 0; j < i; j++) {
list.add(j, getRandomNumber(10, 10000));
MergeSort merge = new MergeSort(list);
merge.sort();
System.out.println(list.getValue(j));
}
}
也是堆栈跟踪：
run:
0
0
Exception in thread "main" java.lang.IndexOutOfBoundsException
at datastructureproject.DoublyLinkedList.getNodes(DoublyLinkedList.java:57)
at datastructureproject.DoublyLinkedList.add(DoublyLinkedList.java:34)
at datastructureproject.MergeSort.sort(MergeSort.java:31)
at datastructureproject.DoublyLinkedList.main(DoublyLinkedList.java:82)
Java Result: 1
BUILD SUCCESSFUL (total time: 0 seconds)
当我调试时：
debug:
0
0
Exception in thread "main" java.lang.IndexOutOfBoundsException
at datastructureproject.DoublyLinkedList.getNodes(DoublyLinkedList.java:57)
at datastructureproject.DoublyLinkedList.add(DoublyLinkedList.java:34)
at datastructureproject.MergeSort.sort(MergeSort.java:31)
at datastructureproject.DoublyLinkedList.main(DoublyLinkedList.java:82)
Java Result: 1
BUILD SUCCESSFUL (total time: 2 seconds)
请多多帮助我。
答案 0 :(得分：2)
这是一个非常规的“答案” - 我将在接下来的几个小时内来到这里，所以我将尽力引导你找到并修复这个错误。
此检查在getNodes中抛出异常：
if (index < 0 || index > length) {
throw new IndexOutOfBoundsException();
为了简化调试，您应始终提供异常信息（请参阅： Effective Java 2nd Edition：第63项：在详细消息中包含故障捕获信息）。帮助我们识别和修复此错误的第一步就是：
if (index < 0 || index > length) {
throw new IndexOutOfBoundsException("Index=" + index + "; length=" + length);
现在，每当抛出异常时，我们都会收到index和length的值的详细信息。
DoublyLinkedList listTwo = new DoublyLinkedList();
for (int x = (localDoublyLinkedList.size() / 2) + 1;
x < localDoublyLinkedList.size(); x++) {
listTwo.add(x, localDoublyLinkedList.getValue(x));
}
很有可能，这是罪魁祸首。当您尝试在索引listTwo添加元素时，x为空。也许你想要这样的东西：
DoublyLinkedList listTwo = new DoublyLinkedList();
for (int x = (localDoublyLinkedList.size() / 2) + 1, offset = x;
x < localDoublyLinkedList.size(); x++) {
listTwo.add(x - offset, localDoublyLinkedList.getValue(x));
}
这使用offset计算，以便listTwo.add从索引0开始。
final局部变量我建议有这样的事情：
final int L = localDoublyLinkedList.size();
final int M = L / 2;
然后在算法中使用L和M来提高可读性。