有一個(gè)類Datacenter，其構(gòu)造函數(shù)是：public Datacenter(        String name,        DatacenterCharacteristics characteristics,        VmAllocationPolicy vmAllocationPolicy,        List<Storage> storageList,        double schedulingInterval) throws Exception {    super(name);    setCharacteristics(characteristics);    setVmAllocationPolicy(vmAllocationPolicy);    setLastProcessTime(0.0);    setStorageList(storageList);    setVmList(new ArrayList<Vm>());    setSchedulingInterval(schedulingInterval);    for (Host host : getCharacteristics().getHostList()) {        host.setDatacenter(this);    }    // If this resource doesn't have any PEs then no useful at all    if (getCharacteristics().getNumberOfPes() == 0) {                throw new Exception(super.getName()                    + " : Error - this entity has no PEs. Therefore, can't process any Cloudlets.");    }    // stores id of this class    getCharacteristics().setId(super.getId());}我們使用這個(gè)類在程序中創(chuàng)建數(shù)據(jù)中心：private static Datacenter createDatacenter(String name, LinkedList myHarddriveList, double timeZone) {    /* Additional codes like defining Hots */    Datacenter datacenter = null;    try {        datacenter = new Datacenter(name, characteristics,                             new VmAllocationPolicySimple(hostList), myHarddriveList, 0);    } catch (Exception e) {                System.out.println("Error: " + e);    }    return datacenter;}程序運(yùn)行結(jié)果如下：?jiǎn)栴}是，如果我通過(guò)擴(kuò)展Datacenter類來(lái)定義自己的數(shù)據(jù)中心，程序?qū)o(wú)法工作。我將MyDatacenter類定義如下：public class MyDatacenter extends Datacenter{    /* My own variables */    public MyDatacenter(String name,            DatacenterCharacteristics characteristics,            VmAllocationPolicy vmAllocationPolicy,           List<Storage> storageList,            double schedulingInterval) throws Exception {        super(name,                 characteristics,                 vmAllocationPolicy,                storageList,                 schedulingInterval);    }    /* My own mwthods */}