Constructor chaining with array in Java

Question

I can't seem to figure out how to chain constructors when the constructor I'm trying to call is supposed to use values passed to the constructor I'm calling it from.

I tried this:

public BoundingBox(Point a, Point b)
{
    Point[] points = {a, b}
    this(points); 
}

but I'm told that the call to this must be on the first line of the constructor.

I'm trying to call this constructor

public BoundingBox(Point[] input)
{
    //do some work
}

Ideally, I could chain these constructors. Otherwise, I may have to restructure my code.

luk2302 · Accepted Answer · 2019-04-04 12:49:06Z

13

That is possible via

this(new Point[] {a, b});

answered Apr 4, 2019 at 12:49

luk2302

57.5k24 gold badges108 silver badges151 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

luk2302 · Accepted Answer · 2019-04-08 11:51:48Z

6

You can replace the two constructor with the following that uses Varargs

public BoundingBox(Point ... input){
    //do some work
}

Brief about Varargs

a method may use a vararg parameter (variable argu- ment) as if it is an array. It is a little different than an array, though. A vararg parameter must be the last element in a method’s parameter list. This implies you are only allowed to have one vararg parameter per method.

When calling a method with a vararg parameter, you have a choice. You can pass in an array, or you can list the elements of the array and let Java create it for you. You can even omit the vararg values in the method call and Java will create an array of length zero for you.

edited Apr 8, 2019 at 11:51

luk2302

57.5k24 gold badges108 silver badges151 bronze badges

answered Apr 4, 2019 at 12:59

malvern dongeni

6814 silver badges10 bronze badges

3 Comments

Eugene Over a year ago

@malverndongeni usually a better definition is public BoundingBox(Point first, Point ... rest){

malvern dongeni Over a year ago

@Eugene you are right.but that approach will require us to define no argument constructor as this case will fail new BoundingBox() moreover,It will force us to supply first Point. *NB there is a brief description of how varargs works which is inline with your approach

luk2302 Over a year ago

The argument for Point first, Point ... rest depends on the use case. If a no-arg constructor is valid, e.g. you can create a BoundingBox without any points then using only one vararg argument is perfectly fine. If on the other hand you always have to have at least one point then you may want to use first, rest approach or even first, second, third, rest depending how many points are the minimum.

Naomi · Accepted Answer · 2019-04-04 12:49:12Z

3

You can use a static function that creates the array

static private Point[] createPointArray(Point a, Point b) 
{ 
    Point[] points = {a, b}
    return points;
}

public BoundingBox(Point a, Point b)
{
    this(createPointArray(a,b)); 
}

answered Apr 4, 2019 at 12:49

Naomi

5,56626 silver badges39 bronze badges

1 Comment

Glains Over a year ago

I really like the static factory method approach, come in handy when creating more complicated objects.

Collectives™ on Stack Overflow

Constructor chaining with array in Java

3 Answers 3

Comments

3 Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

3 Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related