Question

我在向通用链表类中实现add方法时遇到了一些麻烦，该类会在给定索引处添加一个值。但是，在通过测试类运行时，我无法正确执行此操作我遇到以下错误：

1) t31AddtoEmptyList(LinkedListTest$Add2Test)
java.lang.IndexOutOfBoundsException

2) t32AddtoThreeItemList0(LinkedListTest$Add2Test)
java.lang.AssertionError: four element list has wrong size. expected:<4> but was:<3>

3) t35AddtoThreeItemList3(LinkedListTest$Add2Test)
java.lang.IndexOutOfBoundsException

这是我在索引方法中的添加：

public void add(int index, E value){
    if (index < 0 || index >= this.size) {
        throw new IndexOutOfBoundsException();

    //if empty add to front
    }else if(index == 0) {
        front = new ListNode(value, front);
    // if index is last element add to front
    }else if(index == size){
        add(value);
    }else {
        ListNode current = front;
        for (int i = 0; i < index - 1; i++){
            current = current.next;
        }
        current.next = new ListNode(value, current.next);
    }
    this.size++;

}

我全班：

public class LinkedList<E>{

    int size;

    private class ListNode{
        E data;
        ListNode next;

        ListNode(E data) {
            this.data = data;
            next = null;
        }

        ListNode(E data, ListNode next) {
            this.data = data;
            this.next = next;
        }
    }

    private ListNode front;
    private ListNode end;

    // Constructor
    // Construct an empty LinkedList object.
    public LinkedList(){
        this.size = 0;
        this.front = null;
    }

    // Return the size (number of items) in this LinkedList.
    public int size(){
        return size;
    }

    // Return true if this LinkedList has no items.
    // Return false if the size is greater than zero.
    boolean isEmpty(){
        return size() == 0;
    }

    //  Add the given element, value, to the end of the list.
    // appends
    public void add(E value){
        if (front == null) {
            front = new ListNode(value);
        } else {
            ListNode current = front;
            while (current.next != null) {
                current = current.next;
            }
            current.next = new ListNode(value);
        }
        this.size++;
    }

    // Add the given element, value, to the list at the given index.
    // After this operation is complete, get(index) will return value.
    // This operation is only valid for 0 <= index <= size().
    public void add(int index, E value){
        if (index < 0 || index >= this.size) {
            throw new IndexOutOfBoundsException();

        //if empty add to front
        }else if(index == 0) {
            front = new ListNode(value, front);
        // if index is last element add to front
        }else if(index == size){
            add(value);
        }else {
            ListNode current = front;
            for (int i = 0; i < index - 1; i++){
                current = current.next;
            }
            current.next = new ListNode(value, current.next);
        }
        this.size++;

    }

    /*
    // prepend helper method
    //prepend
    public void prepend(int data){
        if (front == null){
            end = new ListNode();
            front = end;
        }
        else {
            front = new ListNode(data,front);
        }
        size++;
    }
    */

    // Return the element of the list at the given index.
    // This operation is only valid for 0 <= index < size().
    // This operation does not modify the list.
    public E get(int index){

        // check for index out of bounds
        if (index < 0 || index >= this.size) {
            throw new IndexOutOfBoundsException();
        }
        // returns char at index
        ListNode curr = front;
        for (int i = 0; i < index; i++) {
            curr = curr.next;
        }
        return curr.data;
    }

} // end class

我的考试班https://gist.github.com/Silverfin13/e22d061c2daf0d3a7013

感谢您的帮助，谢谢

Answer 1

if (index < 0 || index >= this.size) {
    throw new IndexOutOfBoundsException();

index >= this.size顶部的public void add(int index, E value)条件是问题所在我想它应该是index > this.size

为什么呢？如果您想要在最后一个位置添加index的节点，那么它将等于当前size并且它有效。

您还有else if(index == size)这个条件，因此它意味着您希望允许index等于size，但在顶部您要为new IndexOutOfBoundsException();投放public void add(int index, E value)这一点。

尺寸维持方面还有另一个问题。

this.size++;此方法会增加任何有效插入的大小index==size。但是对于else if(index == size){ add(value);

public void add(E value)

您调用index==size方法，如果this.size custom_theme增加两倍，也会在操作结束时增加大小。

在通用链表列

1 个答案: