issue creating a double array list

Question

Is there any reason the fallowing code would give A compile error ?

Import java.util.*;

public class Storageclass
// class used to store the Student data 
{
 // creates the private array list needed. 
 private ArrayList<String> nameList = new ArrayList<String>();
 private ArrayList<double> GPAList = new ArrayList<double>();
 private ArrayList<double> passedList = new ArrayList<double>();
}

this is in a class access by a main file there is more in the class by it not part of this error. when I run this the two double arrayList give me this error.

Storageclass.java:8: error: unexpected type
 private ArrayList<double> GPAList = new ArrayList<double>(1);
                   ^
  required: reference
  found:    double

I am not sure why or what that error means any help would be appreciated.

~ Thanks for the help was a embarrassingly novice mistake I made, but hope full this can help some other person.

Did you at least try to search for this issue on the net before asking? — Luiggi Mendoza
– Luiggi Mendoza, Commented Nov 18, 2013 at 2:31

Pshemo · Accepted Answer · 2013-11-18 03:04:47Z

7

Since all generic types <T> are erased at runtime to Object every type you put in place of T must also extend Object. So you can't set T to be primitive type like double but you can use its wrapper class Double. Try this way:

private List<Double> passedList = new ArrayList<Double>();

or since Java7 little shorter version

private List<Double> passedList = new ArrayList<>();

Also don't worry if you try to add variable of double type to such array since it will be autoboxed to Double.

edited Nov 18, 2013 at 3:04

answered Nov 18, 2013 at 2:33

Pshemo

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Sotirios Delimanolis · Accepted Answer · 2013-11-18 02:31:22Z

2

Primitive types cannot be used as generic type arguments. Use the wrapper type Double (or whichever is appropriate).

answered Nov 18, 2013 at 2:31

Sotirios Delimanolis

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brettw · Accepted Answer · 2013-11-18 02:31:40Z

2

Use ArrayList<Double> instead of ArrayList<double>.

answered Nov 18, 2013 at 2:31

brettw

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2 Comments

Luiggi Mendoza Over a year ago

In fact, OP should use List<Double> instead of ArrayList<Double>.

Justin Over a year ago

@LuiggiMendoza Why should a List be used instead of an ArrayList?

Paul Samsotha · Accepted Answer · 2013-11-18 02:32:03Z

0

cant be primitive type

private ArrayList<double>

use Double

private ArrayList<Double>

answered Nov 18, 2013 at 2:32

Paul Samsotha

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