将双精度数组转换为双精度 ArrayList

发布于 2024-10-20 05:41:18 字数 392 浏览 2 评论 0原文

当我尝试将双精度数组转换为双精度数组列表时，出现以下错误：

线程“main”中的异常 java.lang.ClassCastException: [D 无法转换为 java.lang.Double

下面是我的代码。

double [] firstValueArray ;

ArrayList; firstValueList = new ArrayList (Arrays.asList(firstValueArray));

我正在将此列表与另一个列表进行比较，并将结果分配给另一个双变量。

请让我知道这个错误的原因。

原文

When I try to convert a double array to a Double arrayList I got the following error:

Exception in thread "main" java.lang.ClassCastException: [D cannot be cast to java.lang.Double

Below is my code.

double [] firstValueArray ;

ArrayList <Double> firstValueList = new ArrayList (Arrays.asList(firstValueArray));

I am comparing this list with another list and assign the result to another double variable.

Please let me know the reason for this error.

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断肠人 2024-10-27 05:41:18

唉，Arrays.asList(..) 不适用于基元。 Apache commons-lang 有

Double[] doubleArray = ArrayUtils.toObject(durationValueArray);
List<Double> list = Arrays.asList(doubleArray);

Alas, Arrays.asList(..) doesn't work with primitives. Apache commons-lang has

Double[] doubleArray = ArrayUtils.toObject(durationValueArray);
List<Double> list = Arrays.asList(doubleArray);

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稀香 2024-10-27 05:41:18

使用 Java 8 Streams API 可以实现这一点

DoubleStream.of(doublesArray).boxed().collect(Collectors.toList());

。从 java 16 开始，这变得更加简洁：

DoubleStream.of(doublesArray).boxed().toList();

如果需要返回 ArrayList 作为实现，则使用

DoubleStream.of(doublesArray).boxed().collect(Collectors.toCollection(ArrayList::new));

此单行代码不需要任何其他库。

Using Java 8 Streams API this is achieved with

DoubleStream.of(doublesArray).boxed().collect(Collectors.toList());

Since java 16 this became a bit more concise:

DoubleStream.of(doublesArray).boxed().toList();

If returning an ArrayList as an implementation is required then use

DoubleStream.of(doublesArray).boxed().collect(Collectors.toCollection(ArrayList::new));

This one-liner doesn't require any additional libraries.

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如此安好 2024-10-27 05:41:18

Guava 的版本更短：

List<Double> list = Doubles.asList(doubleArray);

参考：

< a href="http://guava-libraries.googlecode.com/svn/tags/release08/javadoc/com/google/common/primitives/Doubles.html#asList%28double...%29" rel="noreferrer" >Doubles.asList(double ...)

注意：这是一个可变参数方法。所有可变参数方法都可以使用相同类型的数组来调用（但不是相应的装箱/未装箱类型！！）。这两个调用是等效的：

Doubles.asList(new double[]{1d,2d});
Doubles.asList(1d,2d);

此外，Guava 版本不执行完整的遍历，它是基元数组的实时列表视图，仅在访问基元时将基元转换为对象。

Guava's version is even shorter:

List<Double> list = Doubles.asList(doubleArray);

Reference:

Doubles.asList(double ...)

Note: This is a varargs method. All varargs methods can be called using an array of the same type (but not of the corresponding boxed / unboxed type!!). These two calls are equivalent:

Doubles.asList(new double[]{1d,2d});
Doubles.asList(1d,2d);

Also, the Guava version doesn't do a full traverse, it's a live List view of the primitive array, converting primitives to Objects only when they are accessed.

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旧城烟雨 2024-10-27 05:41:18

感谢 bestsss 的评论，这应该是答案：

ArrayList<Double> firstValueList = new ArrayList<Double>();
for(double d : firstValueArray) firstValueList.add(d);

Credit to bestsss for the comment which should be the answer:

ArrayList<Double> firstValueList = new ArrayList<Double>();
for(double d : firstValueArray) firstValueList.add(d);

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他夏了夏天 2024-10-27 05:41:18

…或者使用 Java 1.7：

double[] firstValueArray = new double[] {1.0, 2.0, 3.0};

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

…or with Java 1.7:

double[] firstValueArray = new double[] {1.0, 2.0, 3.0};

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

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