代码和老师的一样，说是初始值设置有问题？

Question

public class SegmentTree<E> {
    private E[] tree;
    private E[] data;
    private Merger<E> merger;

    public SegmentTree(E[] arr, Merger<E> merger){

        this.merger = merger;

        data = (E[])new Object[arr.length];
        for(int i = 0 ; i < arr.length ; i ++)
            data[i] = arr[i];

        tree = (E[])new Object[4 * arr.length];
        buildSegmentTree(0, 0, arr.length - 1);
    }

    // 在treeIndex的位置创建表示区间[l...r]的线段树
    private void buildSegmentTree(int treeIndex, int l, int r){

        if(l == r){
            tree[treeIndex] = data[l];
            return;
        }

        int leftTreeIndex = leftChild(treeIndex);
        int rightTreeIndex = rightChild(treeIndex);

        // int mid = (l + r) / 2;
        int mid = l + (r - l) / 2;
        buildSegmentTree(leftTreeIndex, l, mid);
        buildSegmentTree(rightTreeIndex, mid + 1, r);

        tree[treeIndex] = merger.merge(tree[leftTreeIndex], tree[rightTreeIndex]);
    }

    public int getSize(){
        return data.length;
    }

    public E get(int index){
        if(index < 0 || index >= data.length)
            throw new IllegalArgumentException("Index is illegal.");
        return data[index];
    }

    // 返回完全二叉树的数组表示中，一个索引所表示的元素的左孩子节点的索引
    private int leftChild(int index){
        return 2*index + 1;
    }

    // 返回完全二叉树的数组表示中，一个索引所表示的元素的右孩子节点的索引
    private int rightChild(int index){
        return 2*index + 2;
    }

    @Override
    public String toString(){
        StringBuilder res = new StringBuilder();
        res.append('[');
        for(int i = 0 ; i < tree.length ; i ++){
            if(tree[i] != null)
                res.append(tree[i]);
            else
                res.append("null");

            if(i != tree.length - 1)
                res.append(", ");
        }
        res.append(']');
        return res.toString();
    }

    public static void main(String[] args) {
        Integer[] nums = {-2, 0, 3, -5, 2, -1};
     /*   SegmentTree<Integer> segmentTree = new SegmentTree<Integer>(nums, new Merger<Integer>() {
            @Override
            public Integer merge(Integer a, Integer b) {
                return a + b;
            }
        });*/
        SegmentTree<Integer> segTree = new SegmentTree<Integer>(nums,
                (a, b) -> a + b);
        System.out.println(segTree);
    }
 }

结果：
Exception in thread “main” java.lang.ArrayStoreException: java.lang.Integer
at SegmentTree.SegmentTree.(SegmentTree.java:19)
at SegmentTree.SegmentTree.main(SegmentTree.java:89)

Answer 1

黄阿玛 2020-08-28 23:49:14

看一下是否是import的Object类不是java.lang包下的

Answer 2

liuyubobobo 2020-03-12 05:08:32

尝试一下下载课程的官方代码，在你的环境下运行，看是否有问题？

本小节官方代码传送门：https://git.imooc.com/coding-207/coding-207/src/master/09-Segment-Tree/03-Building-Segment-Tree/src 

Answer 3

慕用5253802 2020-03-11 23:09:47

我把你 代码粘下来试了,没有问题;考虑是环境的问题

• 云霄9 #1

  朋友!我和你一样的!不是环境的问题!
  这句代码有问题
  int mid = l + (r - l) / 2; //这里是r-l (right-left)
  您看看是否一开始写成了right-1(数字1)!! T_T

• 云霄9 #2

  但也许只是我一个人眼瞎...T_T