Initializing objects into an arrayList from test class

Question

Hey I'm new to Java and have been having difficulties with arrays. I'm trying to use either arrays or arrayLists to store a list of values from my test class. But I'm having on how to add set1 and set2 into my arrayList.

I have a test class with

Data set1 = new Data(new double[]{1, 2, 3, 4, 5});
    System.out.println("Set1: " + set1);

Data set2 = new Data(new double[]{-5, -4, -3, 1});
        System.out.println("Set2: " + set2);

Then my data class

    import java.util.ArrayList;

    public class Data {

    public Data(double[] sets) {
        ArrayList<Double> sets = new ArrayList<Double>();
    }

}

you can´t add `set1` and `set2` as they are of the type `Data` and your `ArrayList` requires a `Double` due to generics. You most likely want a constructor `Data(double[])` where you pass the `double` array. in there you could add the values to the `List`. — SomeJavaGuy, Dec 13 '16 at 07:08
Possible duplicate of [Create ArrayList from array](http://stackoverflow.com/questions/157944/create-arraylist-from-array) — kiner_shah, Dec 13 '16 at 07:26

Jeremy Gurr · Answer 1 · 2016-12-13T07:49:32.493

0

Maybe this would work for you:

public Data(double[] array) {
    sets = new ArrayList<Double>(Arrays.asList(array));
}

public String toString() {
    return sets.toString();
}

edited Dec 13 '16 at 07:49

answered Dec 13 '16 at 07:15

Jeremy Gurr

1,613
8
11

How would I resolve set1 to a variable in my toString. Atm if I try to output I get the adress of set1 and set2. – JavaNewbie42 Dec 13 '16 at 07:33

score 0 · Answer 2 · answered Dec 13 '16 at 07:21

Firstly create data class as:

class Data
{
   ArrayList<Double> obj;

   Data(Double var[])
   {
      obj=new  ArrayList<Double>();

      for(int i=0;i<var.length;i++)
      {
           obj.add(var[i]);
      }
   }
}

Now create objects of this data class as:

Double val1[]={1.0,2.0,3.0,4.0};
Data set1=new Data(val1);

Double val2[]={1.0,25.0,36.0,44.0};
Data set2=new Data(val2);

Now add these objects of data class into arraylist as:

ArrayList<Data> sets=new ArrayList<Data>();
sets.add(set1);
sets.add(set2);

score 0 · Accepted Answer · answered Dec 13 '16 at 07:28

Your problem is in your Data class:

import java.util.ArrayList;

public class Data {

    public Data(double[] sets) {
        ArrayList<Double> sets = new ArrayList<Double>();
    }

}

The sets variable disappears after the constructor returns, so there is no use declaring it there. You should move the declaration to the class level and assign a correct value to it in the constructor:

ArrayList<Double> sets;
public Data(double[] sets) {
    this.sets = new ArrayList<Double>();
    for (double d : sets) {
        this.sets.add(d);
    }
}

Since you want to print the Data, you need to override the toString method:

@Override
public String toString() {
    return sets.toString();
}

score 0 · Answer 4 · answered Dec 13 '16 at 11:58

Here is the code using Java 8 streams,

class Data {

    List<Double> d;

    public Data(Stream sets) {
         this.d = (List<Double>) sets.collect(Collectors.toList());
    }
}

Data setss = new Data(Stream.of("1.1","2","3.4","4","5"));
System.out.println("d list = "+setss.d);

Initializing objects into an arrayList from test class

4 Answers4