双打的Java ArrayList

Question

Is there a way to define an ArrayList with the double type? I tried both

ArrayList list = new ArrayList<Double>(1.38, 2.56, 4.3);

and

ArrayList list = new ArrayList<double>(1.38, 2.56, 4.3);

The first code showed that the constructor ArrayList<Double>(double, double, double) is undefined and the second code shows that dimensions are required after double .

Answer 1

Try this:

List<Double> list = Arrays.asList(1.38, 2.56, 4.3);

which returns a fixed size list.

If you need an expandable list, pass this result to the ArrayList constructor:

List<Double> list = new ArrayList<>(Arrays.asList(1.38, 2.56, 4.3));

Answer 2

ArrayList list = new ArrayList<Double>(1.38, 2.56, 4.3);

needs to be changed to:

List<Double> list = new ArrayList<Double>();
list.add(1.38);
list.add(2.56);
list.add(4.3);

Answer 3

尝试这个，

ArrayList<Double> numb= new ArrayList<Double>(Arrays.asList(1.38, 2.56, 4.3));

Answer 4

You are encountering a problem because you cannot construct the ArrayList and populate it at the same time. You either need to create it and then manually populate it as such:

ArrayList list = new ArrayList<Double>();
list.add(1.38);
...

Or, alternatively if it is more convenient for you, you can populate the ArrayList from a primitive array containing your values. For example:

Double[] array = {1.38, 2.56, 4.3};
ArrayList<Double> list = new ArrayList<Double>(Arrays.asList(array));

Answer 5

You can use Arrays.asList to get some list (not necessarily ArrayList) and then use addAll() to add it to an ArrayList:

new ArrayList<Double>().addAll(Arrays.asList(1.38L, 2.56L, 4.3L));

If you're using Java6 (or higher) you can also use the ArrayList constructor that takes another list:

new ArrayList<Double>(Arrays.asList(1.38L, 2.56L, 4.3L));

Answer 6

Try this:

 List<Double> l1= new ArrayList<Double>();
 l1.add(1.38);
 l1.add(2.56);
 l1.add(4.3);

Answer 7

Using guava

Doubles.asList(1.2, 5.6, 10.1);

or immutable list

ImmutableList.of(1.2, 5.6, 10.1);

Answer 8

1) " Unnecessarily complicated " is IMHO to create first an unmodifiable List before adding its elements to the ArrayList.

2) The solution matches exact the question: " Is there a way to define an ArrayList with the double type? "

double type:

double[] arr = new double[] {1.38, 2.56, 4.3};

ArrayList:

ArrayList<Double> list = DoubleStream.of( arr ).boxed().collect(
    Collectors.toCollection( new Supplier<ArrayList<Double>>() {
      public ArrayList<Double> get() {
        return( new ArrayList<Double>() );
      }
    } ) );

…and this creates the same compact and fast compilation as its Java 1.8 short-form:

ArrayList<Double> list = DoubleStream.of( arr ).boxed().collect(
    Collectors.toCollection( ArrayList::new ) );

Answer 9

double[] arr = new double[] {1.38, 2.56, 4.3};

ArrayList<Double> list = DoubleStream.of( arr ).boxed().collect(
    Collectors.toCollection( new Supplier<ArrayList<Double>>() {
      public ArrayList<Double> get() {
        return( new ArrayList<Double>() );
      }
    } ) );