如何在Java 8中从流创建二维数组？ [英] How to create a two dimensional array from a stream in Java 8?

问题描述

我有这样的文字文件：

ids.txt

1000
999
745
123
...

我想读取此文件并将其加载到二维数组中。我希望有一个类似于下面的数组：

I want to read this file and load it in a two dimensional array. I expect to have an array similar to the one below:

Object[][] data = new Object[][] { //
     { new Integer(1000) }, //
     { new Integer(999) }, //
     { new Integer(745) }, //
     { new Integer(123) }, //
     ...
};

这是我写的代码：

File idsFile = ... ;
try (Stream<String> idsStream = Files.lines(idsFile.toPath(), StandardCharsets.US_ASCII)) {
    Object[][] ids = idsStream
       .filter(s -> s.trim().length() > 0)
       .toArray(size -> new Object[size][]);

    // Process ids array here...
}

运行此代码时，会引发异常：

When running this code, an exception is raised:

java.lang.ArrayStoreException: null
at java.lang.System.arraycopy(Native Method) ~[na:1.8.0_45]
at java.util.stream.SpinedBuffer.copyInto(Unknown Source) ~[na:1.8.0_45]
at java.util.stream.Nodes$SpinedNodeBuilder.copyInto(Unknown Source) ~[na:1.8.0_45]
at java.util.stream.SpinedBuffer.asArray(Unknown Source) ~[na:1.8.0_45]
at java.util.stream.Nodes$SpinedNodeBuilder.asArray(Unknown Source) ~[na:1.8.0_45]
at java.util.stream.ReferencePipeline.toArray(Unknown Source) ~[na:1.8.0_45]
... 

如何解决此异常？

推荐答案

给定 Stream< String> ，您可以将每个项目解析为 int 并使用以下内容将其包装到 Object [] 中：

Given a Stream<String> you can parse each item to an int and wrap it into an Object[] using:

 strings
        .filter(s -> s.trim().length() > 0)
        .map(Integer::parseInt)
        .map(i -> new Object[]{i})

现在将结果转换为对象[] [] ，您可以这样做：

Now to turn that result into a Object[][] you can simply do:

Object[][] result = strings
        .filter(s -> s.trim().length() > 0)
        .map(Integer::parseInt)
        .map(i -> new Object[]{i})
        .toArray(Object[][]::new);

输入：

final Stream<String> strings = Stream.of("1000", "999", "745", "123");

输出：

[[1000], [999], [745], [123]]

这篇关于如何在Java 8中从流创建二维数组？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！