How to add Array to ArrayList (Java)

Question

I have a global ArrayList list declared with the intention of adding a float variable to it in a method:

ArrayList<Float[]> list = new ArrayList<Float[]>();

Here is the method:

public void recieve(float[] coords)
{
    this.list.add(?); 
}

What is the syntax for adding coords to the ArrayList?

I cannot test this at the moment but I am reasonable certain your coords parameter will need to be converted to a Float[] (meaning an array of the object wrapper for a primitive float) before adding it to the ArrayList, since the ArrayList is expecting objects of type Float[], not float[]. Other than that, you have it correct. — Paul Richter
– Paul Richter, Commented Nov 27, 2013 at 1:27
I am also not sure that the question is correct. You want to add a float variable, then pass in an array float[]. — user439793
– user439793, Commented Nov 27, 2013 at 1:29
One will need to change if you want to avoid extra conversion steps. Which one it is depends on external factors: are you using some library or framework that needs one or the other? Are you doing a lot of "real" math that would create a lot of extra boxing and unboxing, slowing things down? — user439793
– user439793, Commented Nov 27, 2013 at 1:32

Blub · Accepted Answer · 2013-11-27 01:29:40Z

4

You will have to convert it manually I think.

public void recieve(float[] coords) {
   this.list.add(convertToFloat(coords));
}

public Float[] convertToFloat(float[] coords) {
  Float[] converted = new Float[coords.length];
  for (int i = 0; i < coords.length; i++) {
     converted[i] = Float.valueOf(coords[i]));
  }
  return converted;
}

answered Nov 27, 2013 at 1:29

Blub

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2 Comments

user439793 Over a year ago

Never use the primitive wrapper constructors: either use the valueOf factory methods or just use autoboxing which does the same thing.

Blub Over a year ago

ok i edit it, thanks for the suggestion. What is the reason for that? edit: Ok I just read the javadoc for it which explains it ;)

Óscar López · Accepted Answer · 2013-11-27 01:38:44Z

2

You're looking for this:

public void receive(float[] coords) { // fixed misspelling in name
    Float[] fCoords = new Float[coords.length];
    for (int i = 0; i < coords.length; i++)
        fCoords[i] = coords[i];       // autoboxing takes place here
    this.list.add(fCoords); 
}

Because the ArrayList expects a Float[], but you have a float[] as parameter (notice the difference in letter case!) a manual conversion is required before adding it to the list.

edited Nov 27, 2013 at 1:38

answered Nov 27, 2013 at 1:33

Óscar López

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Comments

REALFREE · Accepted Answer · 2013-11-27 01:27:16Z

0

Since you declare Arraylist type as float array, I believe you can just use as

list.add(coords);

Cheers

answered Nov 27, 2013 at 1:27

REALFREE

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3 Comments

user439793 Over a year ago

This will not work because the ArrayList stores Float[] but the method accepts float[]. Each element will need to be converted.

REALFREE Over a year ago

Ah i didn't notice they are different type.. Why don't you make it to accept Float [] then ?

Paul Richter Over a year ago

@REALFREE You're technically right, if the rest of the program is designed in such a way that they have the freedom to do that. But we just don't have enough information. They'd probably have to convert it at some point along they way anyways. I suppose they could overload the method too if they are so restricted, to handle either scenario.

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