集合比较器报错java.lang.IllegalArgumentException: Comparison method violates its general contract!

 

Collections.sort(listMonthlyUsage, new Comparator<MonthlyUsageDto>() { //按照元素从小到大排序
            @Override
            public int compare(MonthlyUsageDto o1, MonthlyUsageDto o2) {
                if(o1.getCstId() > o2.getCstId())  return 1;
                else return -1;
//                return o1.getCstId() - o2.getCstId();
            }
        });

上面代码报错都是因为我们比较器不够严谨，只有返回1和-1，米有返回0。将代码改为下面就正常了:

Collections.sort(listMonthlyUsage, new Comparator<MonthlyUsageDto>() { //按照元素从小到大排序
            @Override
            public int compare(MonthlyUsageDto o1, MonthlyUsageDto o2) {
                if(o1.getCstId() > o2.getCstId())  return 1;
                else if (o1.getCstId() == o2.getCstId())  return 0;
                else return -1;
//                return o1.getCstId() - o2.getCstId();
            }
        });