从其他类中调用print方法，其中包含原始数据类型

Question

I have been programming in Java using BlueJ for 2 months now and I need some help with an assignment. I am making a basic Vehicle Purchase data entry program. I need to call the printPurchaseDate() method from the PurchaseDate class. The problem I am faced with is that the print statement has three int values: year, month, and day. When I try to call this method in the Vehicle class in the printDetails() method, it tells me that I need a return, if I take away the void I have to label the method as a string. However it doesn't work then because it holds three int variables inside it that conflict with the string method. How can I go about doing this? I basically want to print all of my information including the purchaseDate . My apologies in advance if I did not present my question properly, this is my first post. Thank you for your help.

I have two classes: Purchase Date and Vehicle.

My vehicle class has this method, designed to print out my information:

public void printDetails() {
    System.out.println("Customer:" + " " +
    customer.getFullName());
    System.out.println("Vehicle Description:" + " " + 
    getVehiclePurchased());
    PurchaseDate.printPurchaseDate();
}

Im having issues with printing the date from my PurchaseDate class in my Vehicle class's "printDetails()" method.

/**
  * The Purchase data class
  */

public class PurchaseDate {

    private int year;
    private int month;
    private int day;

    private static final int CURRENT_YEAR = 2014;
    private static final int LAST_MONTH = 12;
    private static final int LAST_DAY = 31;

    /**
     * default constructor
     */
    public PurchaseDate() {
    }

    /**
     * @param year to initialize theYear field
     * @param month to initialize theMonth field
     * @param day to initialize theDay field
     */

    public PurchaseDate(int theYear, int theMonth, int theDay) {
    setYear(theYear);
    setMonth(theMonth);
    setDay(theDay);

    if (year < 1900 || year > 2014) {
            System.out.println("The year value can be no greater than the current year");
        } else {
            this.year = year; }
    if (month < 1 || month > 12) {
            System.out.println("The month value must be between 1 and 12");
        } else {
            this.month = month; }        
    if (day < 1 || day > 31) {
            System.out.println("The day value must be between 1 and 31");
       } else {
            this.day = day; }
    }        
    //Mutators and Accessors    
    /**
     * @return year
     */
    public int getYear() {  
        return year;
    }

    /**
     * @return month
     */
    public int getMonth() {
        return month;
    }

    /**
     * @return day
     */
    public int getDay() {
        return day;
    }

    /**
     * @param the year
     */
    public final void setYear(int newYear) {
        year = newYear;
    }

    /**
     * @param the month
     */
    public final void setMonth(int newMonth) {
        month = newMonth;
    }

    /**
     * @param the day
     */
    public final void setDay(int newDay) {
        day = newDay;
    }

    /**
     * prints the purchase date
     */
    public void printPurchaseDate() {
        System.out.println("The purchase date is:" + " " + year + "-" + month + "-" + day);

    }
}

I basically want my System.out.println to print out the date that I have in my PurchaseDate class.

Answer 1

public void printDetails() {
    System.out.println("Customer:" + " " +
    customer.getFullName());
    System.out.println("Vehicle Description:" + " " + 
    getVehiclePurchased());
    PurchaseDate.printPurchaseDate();
}

The basic problem in your code is that your calling the printPurchaseDate() in static way but it is a non static method. You have to create the refrence of PurchaseDate class and calll the method with the refrence

PurchaseDate pd = new PurchaseDate();
public void printDetails() {
    System.out.println("Customer:" + " " +
    customer.getFullName());
    System.out.println("Vehicle Description:" + " " + 
    getVehiclePurchased());
    pd.printPurchaseDate();
}

Other thing you can do it to declair method static.

public static void printPurchaseDate(){
    // your code here
}

Answer 2

Your method printPurchaseDate() returns void and println() expects something (ie a String). To fix it,

public String printPurchaseDate() {
    return "The purchase date is: " + String.valueOf(year) + "-" + String.valueOf(month) + "-" + String.valueOf(day);
}

That should do the trick.

Answer 3

Either of these ways will solve your problem:

public String getPurchaseDate() {
    return "The purchase date is:" + " " + year + "-" + month + "-" + day; 
}

public void printDetails() {
    System.out.println("Customer:" + " " +
    customer.getFullName());
    System.out.println("Vehicle Description:" + " " +
    getVehiclePurchased());
    System.out.println(PurchaseDate.getPurchaseDate());
}

OR

public void printPurchaseDate() {
    System.out.println("The purchase date is:" + " " + year + "-" + month + "-" + day); 
}

public void printDetails() {
    System.out.println("Customer:" + " " +
    customer.getFullName());
    System.out.println("Vehicle Description:" + " " +
    getVehiclePurchased());
    PurchaseDate.printPurchaseDate();
}