Iinitialization of members. From Qt (C++) to Java

**QtFalcon** · August 3rd, 2014, 12:43 AM

Hi,

Please, help me to write analog of this code in Java:

#include <QString>
 
class Person
{
public:
    Person( QString nickName = QString( "" ),
            QString firstName = QString( "" ),
            QString lastName = QString( "" ),
            QString phoneNumber = QString( "" ),
            QString email = QString( "" )) :
        m_nickName( nickName ),
        m_firstName( firstName ),
        m_lastName( lastName ),
        m_phoneNumber( phoneNumber ),
        m_email( email )
    {
 
    }
 
    // ...
}

**Ada Lovelace** · August 3rd, 2014, 01:17 AM

A good start would be to read up on the differences between
C++ and Java. I'm guessing you made this program using
the Qt Creator IDE (not a fan

- but anyway it's not as simple
as changing one or two phrases. Main is defined differently in
Java as is classes and instances, fields etc.

Once you understand the basic syntactical differences it's not
too hard to accomplish.

Wishes Ada xx

**QtFalcon** · August 3rd, 2014, 02:32 AM

Please, see my code:

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
 
package my.checkpersondata;
 
/**
 *
 * @author Ivan
 */
public class Person
{
    Person( String nickName,
            String firstName,
            String lastName,
            String phoneNumber,
            String email)
    {
        m_nickName = nickName;
        m_firstName = firstName;
        m_lastName = lastName;
        m_phoneNumber = phoneNumber;
        m_email = email;
    }
 
    public void setNickName( String nickName )
    {
        m_nickName = nickName;
    }
 
    public void setFirstName( String firstName )
    {
        m_firstName = firstName;
    }
 
    public void setLastName( String lastName )
    {
        m_lastName = lastName;
    }
 
    public void setPhoneNumber( String phoneNumber )
    {
        m_phoneNumber = phoneNumber;
    }
 
    public void setEmail( String email )
    {
        m_email = email;
    }
 
    public String getNickName()
    {
        return m_nickName;
    }
 
    public String getFirstName()
    {
        return m_firstName;
    }
 
    public String getLastName()
    {
        return m_lastName;
    }
 
    public String getPhoneNumber()
    {
        return m_phoneNumber;
    }
 
    public String getEmail()
    {
        return m_email;
    }
 
    private String m_nickName;
    private String m_firstName;
    private String m_lastName;
    private String m_phoneNumber;
    private String m_email;
}

**Cornix** · August 3rd, 2014, 02:36 AM

Do you have any problems with that code?

**QtFalcon** · August 3rd, 2014, 02:45 AM

No

How to set default values in constructor how in Qt:

class Person
{
public:
    Person( QString nickName = QString( "" ),
            QString firstName = QString( "" ),
            QString lastName = QString( "" ),
            QString phoneNumber = QString( "" ),
            QString email = QString( "" )) :
        m_nickName( nickName ),
        m_firstName( firstName ),
        m_lastName( lastName ),
        m_phoneNumber( phoneNumber ),
        m_email( email )
    {
 
    }
 
    // ...
}

**Ada Lovelace** · August 3rd, 2014, 02:58 AM

You can pass default values to fields via the constructor
parameter. Which in turn would call the 'set' method of
each field to initialize it.

public class Example {
   public Example(int x, int y) {
      setMethodX(x);
      setMethodY(y);
   }
}

Wishes Ada xx

**QtFalcon** · August 3rd, 2014, 04:50 AM

What's the difference between:

public class Example {
   public Example(int x, int y) {
      setMethodX(x);
      setMethodY(y);
   }
}

And:

public class Example {
   public Example(int x, int y) {
      m_x = x;
      m_y = y;
   }
   private String m_x;
   private String m_y;

I want to use Person-object like this:

Person person = new Person();

--- Update ---

I could use this object in Qt like this:

Person person;
person.setFirstName( "Ivan" );

I will use this object in Java like this:

        String nickName = "";
        String firstName = "";
        String lastName = "";
        String phoneNumber = "";
        String email = "";
 
        Person person = new Person( nickName, firstName, lastName,
        phoneNumber, email );

Thanks for everyone!

**Cornix** · August 3rd, 2014, 06:51 AM

You can overload constructors the same way that you can overload any method in java.

public class MyClass {
 
        public MyClass (int i) {
                // Do stuff
        }
 
        public MyClass () {
                this(0); // Default value for i is 0.
        }
 
}

**QtFalcon** · August 3rd, 2014, 07:41 AM

Thanks! It is how in C++

public class Person
{
    Person( String nickName,
            String firstName,
            String lastName,
            String phoneNumber,
            String email)
    {
        m_nickName = nickName;
        m_firstName = firstName;
        m_lastName = lastName;
        m_phoneNumber = phoneNumber;
        m_email = email;
    }
 
    Person( ) {
        m_nickName = "";
        m_firstName = "";
        m_lastName = "";
        m_phoneNumber = "";
        m_email = "";
    }
    // ...

I don't understand this line:

this(0); // Default value for i is 0.

Now I can write instead this code:

    /**
     * Test of setNickName method, of class Person.
     */
    @Test
    public void testSetNickName()
    {
        String nickName = "";
        String firstName = "";
        String lastName = "";
        String phoneNumber = "";
        String email = "";
        Person person = new Person( nickName, firstName, lastName,
                phoneNumber, email );
        person.setNickName( "8Observer8" );
 
        String actual = person.getNickName();
        String expected = "8Observer8";
 
        assertEquals( expected, actual );
    }

This code:

    /**
     * Test of setNickName method, of class Person.
     */
    @Test
    public void testSetNickName()
    {
        Person person = new Person( );
        person.setNickName( "8Observer8" );
 
        String actual = person.getNickName();
        String expected = "8Observer8";
 
        assertEquals( expected, actual );
    }

**Cornix** · August 3rd, 2014, 08:13 AM

The "this" keyword in the constructor is used to call another constructor.
It is usually a better idea to have only a single constructor that initializes member variables, all other constructors call this master constructor and just pass the default values as arguments.
For your very simple example this is not needed, but its just a better style and much safer to have a single point of failure.

**QtFalcon** · August 3rd, 2014, 10:09 PM

This line doesn't work:

this( "", "", "", "", "" );

/**
 *
 * @author Ivan
 */
public class Person
{
    public Person( String nickName,
            String firstName,
            String lastName,
            String phoneNumber,
            String email)
    {
        m_nickName = nickName;
        m_firstName = firstName;
        m_lastName = lastName;
        m_phoneNumber = phoneNumber;
        m_email = email;
    }
 
    public Person( ) {
        this( "", "", "", "", "" );
    }
 
    // ...
 
}

**Junky** · August 3rd, 2014, 10:45 PM

We don't have crystal balls. How does it not work?
Copy and paste full error messages.

**QtFalcon** · August 3rd, 2014, 10:54 PM

Sorry! There are no mistakes

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