java根据元素的自然顺序对列表进行排序

Question

我想要以下代码的降序排序类型：

这是升序排序：

public static <T extends Vm> void sortByCpuUtilization(List<T> vmList) {
    Collections.sort(vmList, new Comparator<T>() {

        @Override
        public int compare(T a, T b) throws ClassCastException {
            Double aUtilization = a.getTotalUtilizationOfCpuMips(CloudSim.clock());
            Double bUtilization = b.getTotalUtilizationOfCpuMips(CloudSim.clock());
            return bUtilization.compareTo(aUtilization);
        }
    });
}

Answer 1

有几种方法可以做到这一点。首先，您可以实现一个反向比较器：

public static <T extends Vm> void sortByCpuUtilizationDesc(List<T> vmList) {
    Collections.sort(vmList, new Comparator<T>() {

        @Override
        public int compare(T a, T b) throws ClassCastException {
            Double aUtilization = a.getTotalUtilizationOfCpuMips(CloudSim.clock());
            Double bUtilization = b.getTotalUtilizationOfCpuMips(CloudSim.clock());
            return aUtilization.compareTo(bUtilization); // Note this is reversed
        }
    });
}

但更优雅的是，您可以使用^{}：

public static <T extends Vm> void sortByCpuUtilizationDesc(List<T> vmList) {
    // Same comparator as before, should be extracted to a named class.
    Collections.sort(vmList, Collections.reverseOrder(new Comparator<T>() {

        @Override
        public int compare(T a, T b) throws ClassCastException {
            Double aUtilization = a.getTotalUtilizationOfCpuMips(CloudSim.clock());
            Double bUtilization = b.getTotalUtilizationOfCpuMips(CloudSim.clock());
            return aUtilization.compareTo(bUtilization); // Note this is reversed
        }
    }));
}

Answer 2

将a与b进行比较：

public static <T extends Vm> void sortByCpuUtilization(List<T> vmList) {
    Collections.sort(vmList, new Comparator<T>() {

        @Override
        public int compare(T a, T b) throws ClassCastException {
            Double aUtilization = a.getTotalUtilizationOfCpuMips(CloudSim.clock());
            Double bUtilization = b.getTotalUtilizationOfCpuMips(CloudSim.clock());
            return aUtilization.compareTo(bUtilization);
        }
    });
}