Java - Populating an array from a constructor

Question

I haven't touched Java in a while now, and I'm a bit confused on how do to this.

I have a class "Foo", which has a private array of ints with size 5.

In the class constructor I need to pass those 5 ints, so I have something like this

public class Foo{

int [] numbers = new int[5];

Foo (int n0, int n1, int n2, int n3, int n4) {
    numbers[0] = n0;
    numbers[1] = n1;
    numbers[2] = n2;
    numbers[3] = n3;
    numbers[4] = n4;
}

This seems like too much work, and there is a simpler way of doing it, I'm just not getting to it. Something like a for loop limited to the array lenght, like

Foo(int n0, int n1, int n2, int n3, int n4, int s0, int s1) {
    for ( int i = o; i<= numbers.length; i++ ) {
         numbers[i]= "n + i";   // This is wrong, but just to get the idea.
    }
}

C'mon, don't over complicate things: public Foo(int[] numbers) { this.numbers = numbers; } — Hovercraft Full Of Eels
– Hovercraft Full Of Eels, Commented Mar 24, 2016 at 1:01
How do I limit my array size in that case ? In the actual code I will need to populate more than one array, so in that solution I'd need to specify the size of earch array in the arguments — Gryxs
– Gryxs, Commented Mar 24, 2016 at 1:07

sprinter · Accepted Answer · 2016-03-24 01:38:44Z

The answer depends somewhat on the context of your solution.

If the 5 integers are from the same domain and are intended to be part of a group then I would suggest passing a single argument that represents that group rather than the 5 separate items. Java provides good mechanisms to create various collections on the fly.

Some potential 'groups' might be:

public Foo(IntStream values) { ... }
new Foo(Stream.of(1, 3, 5, 7, 9));

public Foo(int[] values) {  ... }
new Foo(new int[]{1, 3, 5, 7, 9});

public Foo(int... values) { ... }
new Foo(1, 3, 5, 7, 9);

public Foo(List<Integer> values) { ... }
new Foo(Arrays.asList(1, 3, 5, 7, 9));

All of these provide methods to check the size, or truncate and covert to any internal format you wish. And this will require minimal change if the number of values you wish to send in changes. Hardcoding the specific values will mean the signature of the constructor changes when the number of values change.

On the other hand if the arguments aren't in the same domain but actually represent distinguishable attributes then giving them as individual arguments to the constructor makes sense. However, in this case, storing them internally as a collection doesn't make so much sense so you will likely need to use standard this.bar = bar patterns to store the values in separate variables.

BAS · Accepted Answer · 2016-03-24 01:16:02Z

2

I think the constructor should not be treated as a function that insert (add) objects inside a data structure. If I were to do it, I would write something like this:

Foo(int size) {
   this.numbers = new int[size];
}

void insert(int n, int location) {
   numbers[location] = n;
}

Then you can use a loop to insert from your client program (main) and assign the location with the variable i (for-loop counter). Thats my suggestion.

Note: you might need to handle the possibility of array out of bounds error somehow in your code.

edited Mar 24, 2016 at 1:16

answered Mar 24, 2016 at 1:10

BAS

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