CODEWITHSUNDEEP
javaarraysmultidimensional-array
Matt
Matt

Reputation: 2680

Storing an array of three values in Java

I have a set of three numbers and I want to store multiple copies of this set in an array. for example, If I was doing it in C it would be something like:

struct tParams
{
    int    v;
    double A;
    double n;
};

static struct tParams Params[] = 
{
    { 4230, 1.477404177730177e-04, 1.9565},
    { 3680, 1.920339268755614e-04, 1.925 },
    { 3450, 2.894751026819746e-04, 1.875 },
    { 3295, 4.349905111115636e-04, 1.825 },
    //...
};

How would I go about this in Java?

Thanks

EDIT To clarify, these values will be hard coded and only referenced. If I use a ListArray of classes, it looks like I need to add each object from within a method.

I'm building a class with methods that preform mathematical operations. Some of these methods use the data I am hard coding to get coefficients. In C, the structs are defined within the main mathOperations class, but not in a method.

Upvotes: 5

Views: 7101

Answers (4)

mblinn
mblinn

Reputation: 3274

Depends on just what you're trying to do.

In general, you probably want to use a class in Java where you would have used a struct in c. Something like this would be the most standard way to do it:

public class Params {

    private Integer v;
    private Double a;
    private Double n;

    public Params(int V, double A, double N){
        this.v=V;
        this.a=A;
        this.n=N;
    }
    public Integer getV() {
        return v;
    }
    public void setV(Integer v) {
        this.v = v;
    }
    public Double getA() {
        return a;
    }
    public void setA(Double a) {
        this.a = a;
    }
    public Double getN() {
        return n;
    }
    public void setN(Double n) {
        this.n = n;
    }

}

The short variable names are generally considered poor practice in Javaland for variables with class scope. While it would be possible to do this without the getters and setters by just making the class variables public, that's generally (though by no means universally), considered poor practice as well. For a simple class like this with no behavior, I'd probably just make everything public.

Upvotes: 3

Kaffiene
Kaffiene

Reputation: 713

I think this is the most literal translation of your C code:

  class tParam {
    int    v;
    double A;
    double n;

    private tParam(int v, double A, double n) {
        this.v = v;
        this.A = A;
        this.n = n;
    }
}

tParam[] params = {
    new tParam(4230, 1.477404177730177e-04, 1.9565),
    new tParam(3680, 1.920339268755614e-04, 1.925),
    new tParam(3450, 2.894751026819746e-04, 1.875),
    new tParam(3295, 4.349905111115636e-04, 1.825)
};

It has the advantage of not using all those setters which are redundant for your case since they're 'set once' as you say. Also, given that the data is a static list, there's no point using a List class - the array is fine.

Upvotes: 2

Amokrane Chentir
Amokrane Chentir

Reputation: 30415

Instead of your struct, you could have a class:

public class TParams
{

   private int v;
   private double A;
   private double n;

   public TParams(int v, double A, double n)
   {
      this.v = v;
      this.A = A;
      this.n = n;
   }

   // Getters + Setters
}

Then you can have a list of instances of your class, like this:

ArrayList<TParams> tParamsList = new ArrayList<TParams>();
tParamsList.add(new TParams(4230, 1.477404177730177e-04, 1.9565));
etc.

EDIT

You should be able to do it this way:

TParams tParamsArray[] = { tParams_1, tParams_2, tParams_3 }; //Where tParams_xx are all instances of your TParams class
tParamsList.addAll(Arrays.asList(tParamsArray));

Upvotes: 1

dbyrne
dbyrne

Reputation: 61101

One option is using a class. I don't think having getters and setters is necessary if you are using it for something simple.

public class TParams {
    public int v;
    public double A;
    public double n;
}

If performance is important, I would consider using parallel arrays of primitives. This will be faster because you will avoid the overhead associated with object creation. This is especially true if you are swapping values in and out of the arrays frequently. Google recommends considering this technique if you are doing Android programming. You could wrap the whole thing into a class, looking something like this depending on your needs:

public class TParamsList {
    double[] a
    double[] n;
    int[] v;

    public TParamsList(int size) {
        a = new double[size];
        n = new double[size];
        v = new int[size];
    }

    public void setValue(int slot, int v, double a, double n) {
        a[slot] = a;
        n[slot] = n;
        v[slot] = a;
    }

    public int getV(int slot) {
        return v[slot];
    }

    public int getA(int slot) {
        return a[slot];
    }

    public int getN(int slot) {
        return n[slot];
    }

}

Upvotes: 1

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