Some Questions About Constructors - Topic

Member

Posts: 34,575

Joined: Mar 25 2009

Gold: 12,633.00

May 8 2016 12:34am

First, what if you need a different value for each object...

this is the code the book gives me for constructors

http://pastebin.com/8U6BBztT

i mean, doesn't seem very efficient if each object needs different value....
for instance:
minivan.passengers = 7;
sportscar.passengers = 2;

also i was wondering if you could create a constructor like this, for simpler code (if this works?):
http://pastebin.com/Njb837C2

Minkomonster

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May 8 2016 03:26am

Then you can define a constructor with a parameter.

Code

public class Car
{
private int passengers;

public Car(int passengers)
{
this.passengers = passengers;
}
}

silvermace

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Posts: 3,451

Joined: Feb 26 2010

Gold: 0.20

May 9 2016 02:24pm

Quote (Minkomonster @ May 8 2016 04:26am)

Then you can define a constructor with a parameter.

Code

public class Car
{
private int passengers;

public Car(int passengers)
{
this.passengers = passengers;
}
}

Building off this, you can overoad constructors with different params.

Code

public class Car
{
private int passengers;
private int carType;

public Car(int passengers)
{
this.passengers = passengers;
this.carType = 0; // default value
}

public Car(int passengers, int carType)
{
this.passengers = passengers;
this.carType = carType;
}
}

This post was edited by silvermace on May 9 2016 02:25pm

Leevee

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Joined: Apr 30 2008

Gold: 5,267.97

May 10 2016 02:08am

Additionally, what you tried in your last link is actually correct. You can assign default values to member variables.

Using silvermace's code:

Code

public class Car
{
private int passengers = 4; // at object creation, this variable will be populated with "4" by default.
private int carType = 0; // "0" by default.

public Car(int passengers)
{
this.passengers = passengers; // default variable is overwritten
// Note: carType is not assigned here, which means the default "0" is retained.
}

public Car(int passengers, int carType)
{
this.passengers = passengers; // default variable is overwritten
this.carType = carType; // default variable is overwritten
}
}

This post was edited by howtodisappearcompletely on May 10 2016 02:08am

Kilos138

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Joined: Dec 15 2008

Gold: 66.63

May 10 2016 07:30pm

For your minivans vs sportscars example, you would put the Constructor in a Vehicle superclass.

No need to define separate constructors for each subclass, unless it is adding a state that doesn't exist in the superclass.
Even then, you would use the superclass constructor and just add a new variable into it.

So, Constructors (when used correctly):
Help with class abstraction
Makes your code more simple / more reusable
Will create less side effects
Your code will be easier to add new features to (i.e. a Sedan class)

This post was edited by Kilos138 on May 10 2016 07:36pm

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