日期對象比較 - Java

我遇到需要我比較對Date對象的引用的程序的問題。場景是車輛展示廳，車輛以陣列列表存儲。日期對象比較 - Java

我有一個車輛類別

import java.text.DecimalFormat; 
    import java.util.*; 
    import java.util.Date; 

    public class Vehicle { 

private String manufacturer; 
private String model; 
//private String customerNameSold = null; 
private String vehicleID_VIN; 
private String dateManufacture; 
private String dateSold; 

private boolean beenSold; 

private char taxBand_A_M; 

private double vehicleCost; 
private String emissions; 



private Customer customerNameSold; 
private Date dom; 
//private String manuDate; 
private Date saleDate; 

    //Constructor 7 
    public Vehicle (String manu, String mod, String vin, String dateManu, char tax, double cost){ 

    manufacturer = manu; 
    model = mod; 
    vehicleID_VIN = vin; 
    dateManufacture = dateManu; 
    //Add String to Date 
    dom = new Date(dateManu); 
    taxBand_A_M = tax; 
    vehicleCost = cost; 
    dateSold = null; 
    customerNameSold = null; 

    beenSold = false; 
} 




public String toString() { 

    DecimalFormat df = new DecimalFormat("#.00"); 

    //method calls - do they need this. then method call? 
    String s = "\nManufacturer: " + getManu() 
      + " \nModel: " + getModel() 
      + " \nVIN: " + getVin() 
      + " \nDate of Manufacture: " + getManuDate() 
      + " \nDate of Manufacture (String to Date): " + getManuDate2() 
      + " \nAge of Vehicle: " + getAgeOfVehicle() + " (in WEEKS)" 
      + " \nTax Band: " + getTax() 
      + " \nEmissions: " + cO2() 
      + " \nCost: £" + df.format(getCost()) 
      + " \nHas Vehicle Been Sold: " + getBeenSold() 
      + " \nCustomer: " + getCust() 
      + " \nDate Sold: " + getDateSold() 
      + " \nDate Sold (String to Date): " + getDateSold2(); 


    return s; 

} 

public String getManu() { 

    return manufacturer; 
} 

public String getModel() { 

    return model; 
} 

    //// public String getCust() { 
    ////  
    ////  return customerNameSold; 
    //// } 

public Customer getCust() { 

    return customerNameSold; 
} 

public String getVin() { 

    return vehicleID_VIN; 
} 

    public String getManuDate(){ 

    return dateManufacture; 
} 

public Date getManuDate2() { 

    return dom; 
} 

public String getDateSold(){ 

return dateSold; 

} 

public Date getDateSold2() { 

    return saleDate; 
} 


//CONVENTION SUGGESTS SHOULD BE 'isSold()' 
public boolean getBeenSold() { 

    return beenSold; 
} 

public char getTax() { 


    return taxBand_A_M; 
} 

public double getCost() { 

    //how to format to 2 decimal places? 
    return vehicleCost; 
} 




public void buyVehicle(String sale, Customer cust) { 




    customerNameSold = cust; 

    //Add String to Date 
    saleDate = new Date(sale); 
    dateSold = sale; 
    beenSold = true; 
} 

public String cO2() { 


    switch (taxBand_A_M) { 
     case 'A': 
      emissions = "0-100"; 
      break; 
     case 'B': 
      emissions = "101-110"; 
      break; 
     case 'C': 
      emissions = "111-120"; 
      break; 
     case 'D': 
      emissions = "121-130"; 
      break; 
     case 'E': 
      emissions = "131-140"; 
      break; 
     case 'F': 
      emissions = "141-150"; 
      break; 
     case 'G': 
      emissions = "151-160"; 
      break; 
     default: 
      emissions = null; 
      break; 
    } 

    return emissions; 
} 


public int getAgeOfVehicle() { 

    Date now = new Date(); 
    long diff = now.getTime() - dom.getTime(); 

    long age = (diff/(1000L * 60 * 60 * 24 * 7)); 
    return (int) age; 
}

}

甲陳列室類

import java.util.*; 

    public class Showroom { 

private String showroomName; 
private ArrayList<Vehicle> theVehicles; 
private Vehicle currVeh = null; 
private ArrayList<Vehicle> recentlySold; 
private Date dateSold; 

private long diff; 
private long age; 


     //Constructor Method - Takes the name of the Showroom Object & Creates the array list of vehicles 
     public Showroom(String name) { 
     showroomName = name; 
     theVehicles = new ArrayList<Vehicle>(); 
     } 

public String getName() { 
    return showroomName; 
} 

public void setName(String name) { 
    //this.showroomName if passed in parameter was named showroomName also 
    showroomName = name; 
} 

    public boolean addVehicle(Vehicle newVehicle) { 


    theVehicles.add(newVehicle); 
    currVeh = newVehicle; 
    return true; 


} 

public boolean addVehicleAfterCurrent(Vehicle newVehicle) { 


    theVehicles.add(theVehicles.indexOf(currVeh) + 1, newVehicle); 
    currVeh = newVehicle; 
    return true; 


} 


public Vehicle findVehicle(String vehicleVIN) { 
    for (Vehicle v : theVehicles) { 
     if (v.getVin().equalsIgnoreCase(vehicleVIN)) { 
      System.out.println("Vehicle Found:\n" 
        + v.getManu() + "\n" 
        + v.getModel() + "\n" 
        + v.getVin() + "\n" 
        + theVehicles.indexOf(v) + "\n"); 
      return v; 

      //OR CALL THE toString() METHOD - v.toString() 
     } 
    } 

    System.out.println("Sorry - The Vehicle was not found in the Showroom!\n" 
      + theVehicles.indexOf(vehicleVIN) + "\n"); 

    return null; 
} 

public Vehicle setCurrentVehicle(Vehicle cv) { 

    currVeh = cv; 
    return currVeh; 
} 

public Vehicle getCurrentVehicle() { 
    System.out.println("\nCurrentVehicle: " + currVeh); 
    return currVeh; 
} 

public Vehicle nextVehicle() { 


    int index = theVehicles.indexOf(currVeh); 
    if (index < 0 || index + 1 == theVehicles.size()) { 
     System.out.println("\nEnd of the list"); 
     return null; 
    } 
    Vehicle v = theVehicles.get(index + 1); 
    setCurrentVehicle(v); 
    System.out.println("\nThe Former Next Vehicle & Now Current Vehicle: " + v); 


    return currVeh; 
} 

public Vehicle previousVehicle() { 

    int index = theVehicles.indexOf(currVeh); 
    if (index <= 0) { 
     System.out.println("\nNegative Index -1 Before Start of List"); 
     return null; 
    } 
    Vehicle v = theVehicles.get(index - 1); 
    setCurrentVehicle(v); 
    System.out.println("\nThe Former Previous Vehicle & Now Current Vehicle: " + v); 


    return currVeh; 

} 

public void outputArray() { 
    for (Vehicle nextVehicle : theVehicles) { 
     System.out.println(nextVehicle.getModel() + "\n" + theVehicles.indexOf(nextVehicle)); 
    } 
} 


public void outputShowroomDetails() { 
    System.out.println("\nSHOWROOM NAME: " + showroomName); 
    //output each vehicle in turn 
    System.out.println("THE VEHICLES IN THE SHOWROOM:"); 
    if (theVehicles.isEmpty()) { 
     System.out.println("\n*** There are no Vehicles in the Showroom! ***"); 
    } else { 
     for (Vehicle nextVehicle : theVehicles) { 
      System.out.println(nextVehicle.toString() + "\n" + theVehicles.indexOf(nextVehicle)); 
     } 
    } 

} 

public Vehicle setCurrentVehicleByVIN(String vin) { 


    System.out.println("\n*** ATTEMPTING TO SET CURRENT VEHICLE BY VIN:\n" 
      + vin); 
    Vehicle v = findVehicle(vin); 
    if (v != null) { 
     System.out.println("\nTHE CURRENT VEHICLE: " + "\nARRAY LIST INDEX: " + theVehicles.indexOf(v) 
       + v.toString()); 
    } 
    currVeh = v; 
    return currVeh; 
} 


public boolean deleteVehicle(String vin) { 
    System.out.println("\nATTEMPTING TO DELETE VEHICLE:\n" 
      + "VEHICLE VIN to DELETE: " + vin); 
    Vehicle v = findVehicle(vin); 
    if (v != null) { 
     theVehicles.remove(v); 
     System.out.println("VEHICLE *** " + vin + " *** REMOVED!"); 
     return true; 
    } 
    return false; 
} 

//Method not working - null pointer 'long diff' line 
public ArrayList<Vehicle> getVehiclesSoldRecently() { 

    recentlySold = new ArrayList<Vehicle>(); 


    //Each vehicle has a sale date 
    //Determine the difference between sale date & todays date 
    //If the difference is greater than 14 days (2 weeks) it won't be added to the array 
    //If the difference is less than or equal to 14 days (2 weeks), then they will be added to the array 



    if (theVehicles.isEmpty()) { 
     System.out.println("\n*** The Showroom is Empty!***"); 
    } else 
    { 
     for (Vehicle v : theVehicles) { 

      Date now = new Date(); 




      dateSold = v.getDateSold2(); 


      long diff = now.getTime() - v.getDateSold2().getTime(); 
      long age = (diff/(1000L * 60 * 60 * 24 * 7)); 


      if (age <= 2) { 

       recentlySold.add(v); 
       System.out.println("\nVEHICLES RECENTLY SOLD: " + v.toString()); 
      } 

     } 
    return recentlySold; 

    } 


}

&一個顧客類

public class Customer { 

private String custName = null; 
private String custPhone = null; 
private String custEmail = null; 

public Customer() { 
} 

public Customer(String name) { 

    custName = name; 
    custPhone = "n/a"; 
    custEmail = "n/a"; 

} 

public Customer(String name, String phone) { 

    custName = name; 
    custPhone = phone; 
    custEmail = "n/a"; 

} 

//***CAN'T HAVE A CONSTRUCTOR DETAILING NAME & EMAIL ONLY 
//AS A (String, String) CONSTRUCTOR ALREADY DEFINED 
public Customer(String name, String phone, String email) { 

    custName = name; 
    custPhone = phone; 
    custEmail = email; 

} 

//***AUTO GENERATED GETTERS & SETTERS - this.* 
public String getCustName() { 
    return custName; 
} 

public void setCustName(String custName) { 
    this.custName = custName; 
} 

public String getCustPhone() { 
    return custPhone; 
} 

public void setCustPhone(String custPhone) { 
    this.custPhone = custPhone; 
} 

public String getCustEmail() { 
    return custEmail; 
} 

public void setCustEmail(String custEmail) { 
    this.custEmail = custEmail; 
} 

//***AUTO GENERATED TOSTRING METHOD (THOUGH EDITED FOR FORMAT) 
@Override 
public String toString() { 
    String cust = "\n*** CUSTOMER ***" 
      + "\nName: " + getCustName() 
      + "\nPhone: " + getCustPhone() 
      + "\nEmail: " + getCustEmail(); 

    //System.out.println(cust); 

    return cust; 
}

}

的ShowroomDriver是

public class ShowroomDriver { 

public static void main(String args[]) { 

    Showroom showDrive = new Showroom("ShowroomDriver Showroom"); 

    System.out.println("\n*** OUTPUT SHOWROOM DETAILS ***"); 

    showDrive.outputShowroomDetails(); 

    System.out.println("\n*** CREATE/ADD 4 VEHICLES ***"); 

    Vehicle sdv1 = new Vehicle("Audi", "R8 Spider", "FAVE 101", "MAR-04-2011", 'E', 45000); 
    //Vehicle sdv1 = new Vehicle("Audi", "R8 Spider", "FAVE 101", 03/04/2011, 'E', 45000); 
    System.out.println("\nTesting toString: " + sdv1.toString()); 

    Vehicle sdv2 = new Vehicle("Tesla", "Model S", "ELEC TRIC", "JAN-01-2013", 'A', 55000); 
    //Vehicle sdv2 = new Vehicle("Tesla", "Model S", "ELEC TRIC", 01/01/2013, 'A', 55000); 
    System.out.println("\nTesting to String: " + sdv2.toString()); 

    Vehicle sdv3 = new Vehicle("Ford", "Cortina", "1212 NUM", "JUN-06-2006", 'D', 55000); 
    //Vehicle sdv3 = new Vehicle("Ford", "Cortina", "1212 NUM", 06/06/2006, 'D', 55000); 
    System.out.println("\nTesting to String: " + sdv3.toString()); 

    Vehicle sdv4 = new Vehicle("VW", "Golf MK 1", "DUB DUB", "NOV-11-1971", 'E', 25000); 
    //Vehicle sdv4 = new Vehicle("VW", "Golf MK 1", "DUB DUB", 11/11/1971, 'E', 25000); 
    System.out.println("\nTesting to String: " + sdv4.toString()); 

    showDrive.addVehicle(sdv1); 
    showDrive.addVehicle(sdv2); 
    showDrive.addVehicle(sdv3); 
    showDrive.addVehicle(sdv4); 


    System.out.println("\n*** OUTPUT SHOWROOM DETAILS ***"); 

    showDrive.outputShowroomDetails(); 

    System.out.println("\n*** BUY 2 VEHICLES ***"); 

    Customer cust1 = new Customer("Andrew Antivan", "01785 111 111"); 
    Customer cust2 = new Customer("Belinda Belle", "01782 222 222", "[email protected]"); 

    sdv1.buyVehicle("JUL-07-2013", cust1); 
    sdv2.buyVehicle("MAR-01-2013", cust2); 

    showDrive.outputShowroomDetails(); 

    System.out.println("\n***CREATE 4 VEHICLES ***"); 

    Vehicle purV1 = new Vehicle("Ford", "Fiesta", "NAT NAT", "MAR-09-2006", 'E', 5000); 
    Vehicle purV2 = new Vehicle("Vauxhall", "Corsa", "LEE 123", "JUL-07-2011", 'D', 5500); 
    Vehicle purV3 = new Vehicle("Toyota", "Aygo", "JOHN 32A", "FEB-02-2010", 'E', 2000); 
    Vehicle purV4 = new Vehicle("Marvel", "Bat Mobile", "KA BOOM", "MAR-11-2008", 'C', 3000); 

    System.out.println("\n*** SELL 2 of 4 VEHICLES ***"); 




    System.out.println("\n*** ADD THE 4 NEW VEHICLES TO SHOWROOM ***"); 

    showDrive.addVehicle(purV1); 
    showDrive.addVehicle(purV2); 
    showDrive.addVehicle(purV3); 
    showDrive.addVehicle(purV4); 



    purV1.buyVehicle("DEC-12-2012", cust1); 
    purV2.buyVehicle("DEC-12-2012", cust1); 
    purV3.buyVehicle("OCT-18-2013", cust2); 
    purV4.buyVehicle("OCT-19-2013", cust2); 

      showDrive.outputShowroomDetails(); 

      showDrive.getVehiclesSoldRecently(); 




}

}

的程序被遞增地修改。最初製造日期&銷售作爲字符串對象傳入（硬編碼），但現在必須將其添加爲日期對象。

我遇到的問題僅在我嘗試調用getVehiclesSoldRecently（）方法時才發生。我收到一個空指針異常警告，這表明問題正在發生，因爲該方法中的'diff ...'行。

錯誤接收：

異常在線程「主」顯示java.lang.NullPointerException

在Showroom.getVehiclesSoldRecently（Showroom.java:197）

diff=now.getTime()-v.getDateSold2().getTime();

在ShowroomDriver.main（ShowroomDriver .java：93）

showDrive.getVehiclesSoldRecently();

任何幫助表明w在這裏我會錯誤的將不勝感激。

謝謝。

*編輯*

用於除了那些getDates必須保持不變，這意味着字符串參數必須被傳遞&然後被轉換成日期對象的所有方法的方法簽名。

來源

2013-10-22 flipd.d.mon

這意味着：

v.getDateSold2()

回報null在：

diff=now.getTime()-v.getDateSold2().getTime();

所以你實際上做的是對空對象調用getTime()。在嘗試訪問它之前，您需要檢查v.getDateSold2()是否爲空。

如果它爲空，則可以忽略它或打印其他內容。

來源

2013-10-22 07:55:02 BobTheBuilder

感謝您的回覆。你能否詳細說明你'處理這種情況'的含義？ –

已更新我的回答 – BobTheBuilder

感謝您的更新。所以，我會看看爲什麼可能會調用一個空對象。我想知道它與我的buyVehicle方法有什麼關係？ –

日期對象比較 - Java

回答

相關問題