Why does it throw a runtime error?


  • 0
    C
    /**
     * // This is the interface that allows for creating nested lists.
     * // You should not implement it, or speculate about its implementation
     * public interface NestedInteger {
     *
     *     // @return true if this NestedInteger holds a single integer, rather than a nested list.
     *     public boolean isInteger();
     *
     *     // @return the single integer that this NestedInteger holds, if it holds a single integer
     *     // Return null if this NestedInteger holds a nested list
     *     public Integer getInteger();
     *
     *     // @return the nested list that this NestedInteger holds, if it holds a nested list
     *     // Return null if this NestedInteger holds a single integer
     *     public List<NestedInteger> getList();
     * }
     */
    
    public class NestedIterator implements Iterator<Integer> {
    
    List<NestedInteger> nestedList;
    NestedIterator[] iterators;
    int index;
    public NestedIterator(List<NestedInteger> nestedList) {
        this.nestedList = nestedList;
        this.index = 0;
        this.iterators = new NestedIterator[nestedList.size()];
    }
    
    @Override
    public Integer next() {
        if(nestedList.get(this.index).isInteger())
            return nestedList.get(this.index++).getInteger();
        else
            {
                NestedIterator i = null;
                if(this.iterators[this.index] != null)
                    i = this.iterators[this.index];
                else
                {
                    i = new NestedIterator(nestedList.get(this.index).getList());
                    this.iterators[this.index] = i;
                }
                if(i.hasNext())
                    return i.next();
                else
                {
                    this.index++;
                    return this.next();
                }    
            }
    }
    
    @Override
    public boolean hasNext() {
        if(this.index < nestedList.size())
            return true;
        return false;    
        }
    }
    
    /**
     * Your NestedIterator object will be instantiated and called as such:
     * NestedIterator i = new NestedIterator(nestedList);
     * while (i.hasNext()) v[f()] = i.next();
     */
    

    From my debugging it seems like the program crashes at the first if condition of the next() function. But why?


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