Adding an Array to an ArrayList

Question

Well hi there! I am making a game called DoorElementals, and I want to do this:

ArrayList<Color> colors = new ArrayList<Color>();
public Door(Color... colors) {
  this.colors.add(colors);
}
public void addColor(Color... c){
  this.colors.add(c);
}

But colors is an array while this.colors is an ArrayList. How should I go about this?

If you want to add an array of Color to the ArrayList change it like ArrayList<Color[]> colors = new ArrayList<>(); — SubOptimal
– SubOptimal, Commented Feb 18, 2015 at 15:37
a simple for (Color c : colors) {this.colors.add(c);} works too. — njzk2
– njzk2, Commented Feb 18, 2015 at 15:42

cole.markham · Accepted Answer · 2015-02-18 15:40:10Z

2

The java.util.Arrays class provides a method to convert from an array to a List.

ArrayList<Color> colors = new ArrayList<Color>();
public Door(Color... colors) {
   this.colors.addAll(Arrays.asList(colors));
}
public void addColor(Color... c){
   this.colors.addAll(Arrays.asList(c));
}

A better practice would be to make your constructor take a Collection instead of a using the varargs.

List<Color> colors = new ArrayList<Color>();
public Door(Collection<Color> colors) {
   this.colors.addAll(colors);
}

answered Feb 18, 2015 at 15:40

cole.markham

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2 Comments

Giulio Franco Over a year ago

You always have this dualism in Java: array world vs collection world. I don't think it really matters who deals with this. The library provides functions to do the trick. So probably, unless there are optimization reasons to implement both versions, it's just easier to only implement the best one, and let the user convert if he needs it. This has the advantage of implicitly pushing the user use to use the fast version whenever he can.

cole.markham Over a year ago

Sure varargs are cool, but that doesn't make using them a good practice.

João Vitor Verona Biazibetti · Accepted Answer · 2015-02-18 16:02:08Z

1

DO NOT USE Arrays.asList. Depending on the amount of calls you do, it will impact the performance, since everytime you call the asList method, a new List is created.

You can, and should, use:

public Door(Color... colors) {
  addAll(colors);
}

public void addAll(Color... colors) {
  for (Color color : colors) {
    myList.add(color);
  }
}

answered Feb 18, 2015 at 16:02

João Vitor Verona Biazibetti

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1 Comment

Aly Over a year ago

Being me, I didn't remember that you can call methods inside of a constructor. Thanks!

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