java - 从Java中的集合中删除

Question

我不明白为什么这段代码会打印错误。这怎么可能？

Set<Set<Place>> clusters = new HashSet<Set<Place>>();  
...         
Set<Place> max1 = null;
Set<Place> max2 = null;
double maxSim = 0;
for (Set<Place> placesSet : clusters) {
    for (Set<Place> placesSet2 : clusters) {
        if (placesSet != placesSet2) {
            double sim = calculateSim(placesSet, placesSet2);

            if (sim >= maxSim) {
                maxSim = sim;
                max1 = placesSet;
                max2 = placesSet2;
            }
        }
    }
}
if (!clusters.remove(max2)) {
    System.out.println("ERROR");
}

编辑 现在我检查 sim 是否小于 0 并且 cluster 是否有多个元素。仍然出现错误

    Set<Place> max1 = null;
    Set<Place> max2 = null;
    double maxSim = 0;
    for(Set<Place> placesSet : clusters) {
        for(Set<Place> placesSet2 : clusters) {
            if(!placesSet.equals(placesSet2)) {
                double sim = calculateSim(placesSet, placesSet2);
                if(sim < 0) sim = 0;
                if(sim >= maxSim) {
                    maxSim = sim;
                    max1 = placesSet;
                    max2 = placesSet2;
                }
            }

        }
    }


    if(!clusters.remove(max2) && clusters.size() >= 1) {
        System.out.println("ERROR");
    }

下一次编辑:

仍然错误:(

Set<Place> max1 = null;
            Set<Place> max2 = null;
            double maxSim = 0;
            for(Set<Place> placesSet : clusters) {
                for(Set<Place> placesSet2 : clusters) {
                    if(!placesSet.equals(placesSet2)) {
                        double sim = calculateSim(placesSet, placesSet2);
                        if(sim < 0) sim = 0;
                        if(sim >= maxSim) {
                            maxSim = sim;
                            max1 = placesSet;
                            max2 = placesSet2;
                        }
                    }

                }
            }


            if(max2 != null && !clusters.remove(max2) && clusters.size() > 1) {
                System.out.println("ERROR");
            }

Answer 1

似乎有两种可能性:

1. calculateSim() 返回负值。由于 sim 永远不会 >= 0，因此您的 if 语句永远不会被执行，并且 max2 将为 null。
2. cluster 有 0 个或 1 个元素。如果没有元素，则循环将永远不会执行。如果有一个元素，循环将执行，但该元素将等于其自身，因此您的第一个 if 将失败。

我建议使用 anding print 语句来监视代码的执行

编辑:请实际将打印语句插入到您的代码中:

       Set<Place> max1 = null;
        Set<Place> max2 = null;
        double maxSim = 0;
        System.out.printf("clusters has %d elements:%s%n",clusters.size,clusters);
        for(Set<Place> placesSet : clusters) {
            for(Set<Place> placesSet2 : clusters) {
                System.out.printf("%ncomparing %s and %s%n",placesSet,placesSet2);
                if(!placesSet.equals(placesSet2)) {
                    System.out.println("The sets are not the same");
                    double sim = calculateSim(placesSet, placesSet2);
                    System.out.printf("The sim of the sets is %f%n",sim);
                    if(sim < 0) sim = 0;
                    System.out.printf("Comparing to the max sim %f%n",maxSim);
                    if(sim >= maxSim) {
                        System.out.println("Found new max sim");
                        maxSim = sim;
                        max1 = placesSet;
                        max2 = placesSet2;
                    }
                }

            }
        }
        System.out.printf("The max is %s%n",max2);

        if(max2 != null && !clusters.remove(max2) && clusters.size() > 1) {
            System.out.println("ERROR");
        }