Date构造函数新的抽象类

Question

I am new to Java and am trying to apply elements of Java that I recently read such as inheritance, arrays, and abstract classes.

I have a base class named Person3. I am trying to use the Date class to get the person's birth date.

I am receiving this error: no suitable constructor found for Date(Date[]) in five places shown below with a comment.

I am researching why this error is occurring and I am not understanding.

Can anyone please explain this error (these errors) in detail? Thank you!

public abstract class Person3 extends Object{

    private String [] name;
    private Date [] birthdate;
    private int [] social;

    public Person3()
    {
         for(int i = 0; i < name.length; i++) {
        System.out.println("INSIDE");
            name[i] = "No name";
        }

        // birthdate = new Date("Jan", 1, 1000);
    for(int i = 0; i < birthdate.length; i++){
        birthdate[i]= new Date ("Jan", 1, 1000);
    }

         //social = 00000000;
    for(int i = 0; i < social.length; i++) {
            social[i] = 00000000;
        }

    }

    /**
     Precondition: Neither theName nor theDate is null.
    */
    public Person3(String [] theName, Date [] theDate, int [] theSocial)
    {
        if (theName == null || theDate == null || theSocial == null)
        {
             System.out.println("Fatal Error creating employee.");
             System.exit(0);
        }
        name = theName;
        birthdate = new Date(theDate); //ERROR
        social = theSocial;
    }

    public Person3(Person3 originalObject)
    {
         name = originalObject.name;
         birthdate = new Date(originalObject.birthdate);  //ERROR
         social = originalObject.social;
    }


    abstract double getPay( );


    public String [] getName( )
    {
        return name;
    }

    public Date [] getbirthDate( )
    {
        return new Date(birthdate); //ERROR
    }

    public int [] getSocial(){
        return social;
    }
    /**
     Precondition newName is not null.
    */
    public void setName(String [] newName)
    {
        if (newName == null)
        {
             System.out.println("Fatal Error setting employee name.");
             System.exit(0);
        }
       else
            name = newName;
    }

    /**
     Precondition newDate is not null.
    */
    public void setBirthDate(Date [] newDate)
    {
        if (newDate == null)
        {
             System.out.println("Fatal Error setting person birthdate.");
             System.exit(0);
        }
        else
            birthDate = new Date(newDate);   //ERROR
    }

    public void setSocial(int [] newSocial){
        if(newSocial == null){
            System.out.println("Fatal Error setting person social.");
            System.exit(0);
        }
    }
}

Answer 1

Date doesn't have a constructor that takes an array, but you do have a birthdate field which is a Date array. I think you wanted

public Person3(String [] theName, Date [] theDate, int [] theSocial)
{
    if (theName == null || theDate == null || theSocial == null)
    {
         System.out.println("Fatal Error creating employee.");
         System.exit(0);
    }
    name = theName;
    birthdate = theDate;
    social = theSocial;
}

and

public Person3(Person3 originalObject)
{
     name = originalObject.name;
     birthdate = originalObject.birthdate;
     social = originalObject.social;
}

and

public Date [] getbirthDate( )
{
    return birthdate;
}

and

public void setBirthDate(Date [] newDate)
{
    if (newDate == null)
    {
         System.out.println("Fatal Error setting person birthdate.");
         System.exit(0);
    }
    else
        birthDate = newDate;
}

because new Date creates a single Date instance; not an array of Date (s).

Answer 2

The constructor of Person3 declares an array for thedate. Valid constructors for Date are ( javadoc )

public Date(int year, int month, int day)
//Deprecated. 
//instead use the constructor Date(long date)

public Date(long date)
//Constructs a Date object using the given milliseconds time value.

Therefore change your constructor

Person3(String [] theName, Date theDate, int [] theSocial)
{
    if (theName == null || theDate == null || theSocial == null)
    {
         System.out.println("Fatal Error creating employee.");
         System.exit(0);
    }
    name = theName;
    birthdate = theDate;
    social = theSocial;
}

And the birthdate class attribute

private Date birthdate;

Answer 3

The accepted Answer by Elliott Frisch is correct and excellent. I've nothing to add there. Instead I'll address two tangents.

java.time

As of Java 8 and later, the new java.time framework ( Tutorial ) supplants the old java.util.Date/.Calendar classes.

I especially want to point this out to someone new to Java and just learning object-oriented programming . The old date-time classes bundled with early versions of Java were a brave attempt at handling date-time, a first for the information technology industry. But in the end they failed. Their faults include some poor OOP design choices. So do not look at them as good examples. Better to avoid them entirely, and focus on java.time instead.

Proper Objects

Your Person3 class design seems to show that you misunderstand the proper use of a class. A class to represent people means each instance of that class should describe a single person. Then we use collections to gather multiple Person objects as "people".

Instead, you seem to have a spreadsheet-like arrangement in your mind. Looks like you are trying to have two-dimensional array listing a person in each row and attributes as columns, then shoe-horning that pseudo-spreadsheet inside an object. That shoe-horning does you no good as you are not take advantage of the benefits of OOP.

Here is a re-worked version to demonstrate OOP design and use of java.time.

While you certainly can use plain arrays in Java (with the [] notation), we often make use of the Collections classes such as a List used here. Notice polymorphism in action where an ArrayList is presented as a List .

Note that java.time classes generally use static factory methods to instantiate objects rather than new . So LocalDate.of() rater than new LocalDate() . Also note that a time zone is required to determine a date such as "today".

package timestuff;

import java.time.LocalDate;
import java.time.Period;
import java.time.ZoneId;
import java.time.ZoneOffset;
import java.util.ArrayList;
import java.util.List;

public class Person {

    private String name;
    private LocalDate dateOfBirth;
    private String favoriteColor;

    public Person ( String name , LocalDate dateOfBirth , String favoriteColor ) {
        this.name = name;
        this.dateOfBirth = dateOfBirth;
        this.favoriteColor = favoriteColor;
    }

    public Integer yearsOld () {
        ZoneId zoneId = ZoneOffset.UTC;
        LocalDate today = LocalDate.now ( zoneId );
        Period age = Period.between ( this.dateOfBirth , today );
        Integer years = age.getYears ();
        return years;
    }

    @Override
    public String toString () {
        return "Person{ " + "name=" + name + " | dateOfBirth=" + dateOfBirth + " | favoriteColor=" + favoriteColor + " }";
    }

    public static void main ( String[] args ) {
        Person julie = new Person ( "Julie" , LocalDate.of ( 1954 , 1 , 7 ) , "purple" );
        Person jeanluc = new Person ( "Jean-Luc" , LocalDate.of ( 1965 , 2 , 22 ) , "blue" );
        Person lisa = new Person ( "Lisa" , LocalDate.of ( 1977 , 3 , 18 ) , "green" );

        List<Person> people = new ArrayList<> ();
        people.add ( julie );
        people.add ( jeanluc );
        people.add ( lisa );

        System.out.println ( "people: " + people );
        System.out.println ( "" );  // blank line.

        System.out.println ( "-- Age Report --" );
        for ( Person person : people ) {
            System.out.println ( person.name + " : " + person.yearsOld () );
        }

    }

}

When run.

people: [Person{ name=Julie | dateOfBirth=1954-01-07 | favoriteColor=purple }, Person{ name=Jean-Luc | dateOfBirth=1965-02-22 | favoriteColor=blue }, Person{ name=Lisa | dateOfBirth=1977-03-18 | favoriteColor=green }]

-- Age Report --

Julie : 61

Jean-Luc : 50

Lisa : 38