How to give input for the double[] array in Java

Question

How do I give input directly, when that function is invoked in another method, especially when that input is a double[] array?

public double dotPro1(double[] vectorA, double[] vectorB) {
    double[] vecPro;
    vecPro = new double[2];
    vecPro[0] = vectorA[0]*vectorB[0];
    vecPro[1] = vectorA[1]*vectorB[1];
    return vecPro[0] + vecPro[1];
}
public double dotPro2(double[] length) {
    double[] lenPro;
    lenPro = new double[1];
    lenPro[0] = length[0];
    return lenPro[0];
}
public static double cosine(double a) {
    double x = Math.cos(Math.toRadians(a));
    /*Class c = Class.forName("NaiveStrategy");
        Class methodTypes[] = new Class[3];
        methodTypes[0] = Double.TYPE;
        methodTypes[1] = Double.TYPE;
        methodTypes[2] = Double.TYPE;
        Method[] m = c.getMethods();*/
    NaiveStrategy ns = new NaiveStrategy();
  problem-->ns.dotPro1(vectorA[], vectorB[]);
  problem-->ns.dotPro2(length[]);
    return 0;  
}

As you can also see my old coding I tried in another way to solve it, but it didn't worked. It's commented out above.

At which place are you facing the problem..can u pin point it — Kumar Vivek Mitra
– Kumar Vivek Mitra, Commented Sep 17, 2012 at 5:58
Why isn't dotPro2 just { return length[0]; }? What's with all the useless double[] manipulation? — nneonneo
– nneonneo, Commented Sep 17, 2012 at 6:00
@basiljames, actually its not useful, i need an array of values to getValues for the length that is magnitude of the vectors in double — visanio_learner
– visanio_learner, Commented Sep 17, 2012 at 6:04

Jon Skeet · Accepted Answer · 2012-09-17 06:03:12Z

3

It's not at all clear what you mean - but certainly the syntax you've got at the moment won't work. If you're just looking to create an array at execution time, that's easy:

NaiveStrategy ns = new NaiveStrategy();
// Either using separate variables...
double[] first = { 0.5, 0.1, 10 };
double[] second { 5, 20.3, 1 };
double result1 = ns.dotPro1(first, second);

// Or inline...
double results2 = ns.dotPro2(new double[] { 50.2, 0.3 });

I can't tell why you've got commented-out reflection calls in your code though...

Also, as noted in comments, your methods seem to be creating arrays for no particular purpose. They could be rewritten as:

public double dotPro1(double[] vectorA, double[] vectorB) {
    return vectorA[0] * vectorB[0] + vectorA[1] * vectorB[1];
}

public double dotPro2(double[] length) {
    return length[0];
}

edited Sep 17, 2012 at 6:03

answered Sep 17, 2012 at 5:59

Jon Skeet

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Comments

Joseph Gardiner · Accepted Answer · 2012-09-17 07:50:43Z

1

You said in one comment that you want random values. So use the Random class to generate them.

double[] list1 = new double[5];
double[] list2 = new double[5];
Random rand = new Random();
for (int i = 0; i < list1.length; i++) {
    list1[i] = rand.nextDouble();
}

for (int i = 0; i < list2.length; i++) {
    list2[i] = rand.nextDouble();
}

The new double[5]; will create an array of length 5. Change this number to the length you want.

Note: rand.nextdouble only gives a random number between 0 and 1. If you wish it to , say, be between 0 and 100 then use rand.nextDouble()*100

You can then just use

double result1 = ns.dotPro1(list1, list2);

answered Sep 17, 2012 at 7:50

Joseph Gardiner

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Comments

basiljames · Accepted Answer · 2012-09-17 06:01:35Z

0

When passing the array parameter do not put the square braces.

= ns.dotPro2(length);
= ns.dotPro1(vectorA, vectorB);

answered Sep 17, 2012 at 6:01

basiljames

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1 Comment

visanio_learner Over a year ago

i know i am just showing my problem here. how do i directly assign values for my array here.

Kumar Vivek Mitra · Accepted Answer · 2012-09-17 06:15:13Z

0

Sorry for the delay, as my net went off..... Ok back to the answer...

Here is the simplest way to do it...

double[] first = { 0.10, 0.15, 0.30 };
double[] second { 65, 44.3, 10.11 };
double result1 = ns.dotPro1(first, second);

answered Sep 17, 2012 at 6:15

Kumar Vivek Mitra

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4 Comments

visanio_learner Over a year ago

thank you for the answer, but i need runtime input values for arrays

Kumar Vivek Mitra Over a year ago

@so whats the probs in it..you can always input double variables into array during runtime... but i would suggest you to use Collection than going for array..its more flexible..

visanio_learner Over a year ago

actually i am new to java programming! it would be nice if i get answers exactly what i need from you?

visanio_learner Over a year ago

actually the answer u suggested me might help me generating just that declared value inside the braces, but i need random values to be generated.

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