java - 列表过程中的无限循环

Question

我有以下代码块:

ArrayList<ELPERouteStop> candidates = new ArrayList<>();
    for (int i=0; i < metric.length;i++) 
    {

        /*
         * We get a from object for each row (customer) and a to object for the element
         * of the matrix with the highest metric from the ith customer.
         */
        ELPERouteStop from = all_stops.get(i);
        ELPERouteStop to = all_stops.get(getMaxValue(metric[i]));
        if(i==0)
        {   
            candidates.add(from);
            candidates.add(to);
        }
        for (int j=0; j < candidates.size();j++)
        {
            int k=0;
            if (candidates.get(j) == from || candidates.get(j)==to) 
            {
                k++;
            }
            if (k == 0)
            {
                candidates.add(from);
                candidates.add(to);
            }
        }
    }

问题似乎在于每次迭代时候选列表大小的变化。我需要将 from 和 to 对象插入到候选列表中，前提是它们尚不存在。因此，我在第二个 for 循环中进行检查。当我运行代码时，它似乎进入无限循环，但我找不到原因。预先感谢您!

Answer 1

您可以使用Collection#contains，而不是每次都迭代集合。

List<ELPERouteStop> candidates = new ArrayList<>();
for (int i=0; i < metric.length;i++) {

    ELPERouteStop from = all_stops.get(i);
    ELPERouteStop to = all_stops.get(getMaxValue(metric[i]));

    if (!candidates.contains(from) && !candidates.contains(to)) {
        candidates.add(from);
        candidates.add(to);
    }
}

或者，稍微更高效 - 取决于 getMaxValue 的速度:

for (int i=0; i < metric.length;i++) {

    ELPERouteStop from = all_stops.get(i);
    if (!candidates.contains(from)) {
        ELPERouteStop to = all_stops.get(getMaxValue(metric[i]));
        if (!candidates.contains(to)) {
            candidates.add(from);
            candidates.add(to);
        }
    }
}