尝试比较日期时发生nullpointerexception。我注意到在调试时，expecteddate和arriveddate变量值正在获取当前日期时间，因为我正在使用set方法设置日期。请更正用于比较日期的代码。我的方法是用来确定货物是否会准时到达，是在预期的时间之前还是之后。

public class ShipmentBO {

    public void displayStatusOfShipment(Shipment shipment) {

        Date expectedDate = new Date();
        Date arrivedDate = new Date();
        SimpleDateFormat df = new SimpleDateFormat("dd-MM-yyyy");

        Shipment s = new Shipment();
        ShipmentStatus SStatus = new ShipmentStatus();
        expectedDate = s.getexpectedDeliveryDate();
        arrivedDate = SStatus.getarrivedDate();

        String s1 = df.format(expectedDate);
        String s2 = df.format(arrivedDate);

        if (expectedDate.after(arrivedDate)) {
            System.out.println("The shipment arrived after the expected date");
        } else
        if (expectedDate.before(arrivedDate)) {
            System.out.println("The shipment arrived before the expected date");
        }
    }

我把日期定在下面的主课上

public static void main(String[] args) throws ParseException {

     Scanner sc = new Scanner(System.in);
     System.out.println("Enter the shipment details :");
     String userDetail = sc.nextLine();
     String userDetailParts[] = userDetail.split(",");
      //System.out.println(Arrays.toString(userDetailParts));

     Shipment shipment = new Shipment();
     SimpleDateFormat sdf = new SimpleDateFormat("dd-MM-yyyy"); 
     shipment.setid(userDetailParts[0]); 
     shipment.setsourcePort(userDetailParts[1]); 
     shipment.setdestinationPort(userDetailParts[2]);
     shipment.setexpectedDeliveryDate(sdf.parse(userDetailParts[3])); 
     shipment.setcustomerName(userDetailParts[4]);
}

我的输入是用逗号分隔的-staju01，香港，cochin，20-05-2017，karthick
装运类别：

import java.util.Date;

public class Shipment {
    private String id;
    private String sourcePort;
    private String destinationPort;
    private Date expectedDeliveryDate;
    private String customerName;
    private ShipmentStatus[] shipmentStatus;

    public String getid() {
        return id;
    }

    public void setid(String id) {
        this.id = id;
    }

    public String getsourcePort() {
        return sourcePort;
    }

    public void setsourcePort(String sourcePort) {
        this.sourcePort = sourcePort;
    }

    public String getdestinationPort() {
        return destinationPort;
    }

    public void setdestinationPort(String destinationPort) {
        this.destinationPort = destinationPort;
    }

    public Date getexpectedDeliveryDate() {
        return expectedDeliveryDate;
    }

    public void setexpectedDeliveryDate(Date expectedDeliveryDate) {
        this.expectedDeliveryDate = expectedDeliveryDate;
    }

    public String getcustomerName() {
        return customerName;
    }

    public void setcustomerName(String customerName) {
        this.customerName = customerName;
    }

    public Shipment() {
    }

    public Shipment(String id, String sourcePort, String destinationPort, Date expectedDeliveryDate,
            String customerName) {
        this.id = id;
        this.sourcePort = sourcePort;
        this.destinationPort = destinationPort;
        this.expectedDeliveryDate = expectedDeliveryDate;
        this.customerName = customerName;
    }

    public ShipmentStatus[] getShipmentStatus() {
        return shipmentStatus;
    }

    public void setShipmentStatus(ShipmentStatus[] shipmentStatus) {
        this.shipmentStatus = shipmentStatus;
    }
}

发货状态：

import java.util.Date;

public class ShipmentStatus {
    private String arrivalPort;
    private String departurePort;
    private Date arrivedDate;
    private String status;
    private Shipment shipment;

    public Shipment getshipment() {
        return shipment;
    }

    public void setshipment(Shipment shipment) {
        this.shipment = shipment;
    }

    public String getarrivalPort() {
        return arrivalPort;
    }

    public void setarrivalPort(String arrivalPort) {
        this.arrivalPort = arrivalPort;
    }

    public String getdeparturePort() {
        return departurePort;
    }

    public void setdeparturePort(String departurePort) {
        this.departurePort = departurePort;
    }

    public Date getarrivedDate() {
        return arrivedDate;
    }

    public void setarrivedDate(Date arrivedDate) {
        this.arrivedDate = arrivedDate;
    }

    public String getstatus() {
        return status;
    }

    public void setstatus(String status) {
        this.status = status;
    }

    public ShipmentStatus() {
    }

    public ShipmentStatus(String arrivalPort, String departurePort, Date arrivedDate, String status,
            Shipment shipment) {
        this.arrivalPort = arrivalPort;
        this.departurePort = departurePort;
        this.arrivedDate = arrivedDate;
        this.status = status;
        this.shipment = shipment;
    }
}