如何转换双[]翻番[]？ [英] How do I convert Double[] to double[]?

问题描述

我实施具有类似于可以包含一个类型的对象的表功能的接口。接口规定了以下功能：

 双击[] getDoubles（INT参数：columnIndex）;
 

在哪里我难倒的是，在我的实现，我存储在2D 对象表数据阵列（对象[] [ ]数据）。当我需要返回的值，我想要做以下（假设getDoubles（）将只包含双打一列被调用，所以不会有ClassCastExceptions异常）：

 双击[] getDoubles（INT参数：columnIndex）{
    返回（双[]）的数据[参数：columnIndex]
}
 

但是 - Java不允许对象[]被丢加倍[]。它铸造到双[]是可以的，因为双击是一个对象，而不是一个原始的，但我的接口指定该数据将作为返回双[ ] 。

所以，我有两个问题：

1. 有什么办法，我可以得到列的数据出了对象[] []表中，并返回原语数组​​？


2. 如果我更改接口以双倍返还[]，会有任何性能影响？

解决方案

不幸的是，你会需要遍历整个列表，然后拆箱双击，如果你想将其转换到双[] 。

至于性能也越高，有在Java装箱和拆箱图元相关的一些时间。如果集合足够小，你不会看到任何性能问题。

I'm implementing an interface that has functionality similar to a table that can contain an types of objects. The interface specifies the following function:

double[] getDoubles(int columnIndex);

Where I'm stumped is that in my implementation, I'm storing the table data in a 2D Object array (Object[][] data). When I need to return the values, I want to do the following (it is assumed that getDoubles() will only be called on a column that contains doubles, so there will be no ClassCastExceptions):

double[] getDoubles(int columnIndex) {
    return (double[]) data[columnIndex];
}

But - Java doesn't allow Object[] to be cast to double[]. Casting it to Double[] is ok because Double is an object and not a primitive, but my interface specifies that data will be returned as a double[].

So I have two questions:

1. Is there any way I can get the column data out of the Object[][] table and return the array of primitives?
2. If I do change the interface to return Double[], will there be any performance impact?

解决方案

Unfortunately you will need to loop through the entire list and unbox the Double if you want to convert it to a double[].

As far as performance goes, there is some time associated with boxing and unboxing primitives in Java. If the set is small enough, you won't see any performance issues.

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