使 arrayList.toArray() 返回更具体的类型 [英] make arrayList.toArray() return more specific types

问题描述

所以，通常 ArrayList.toArray() 会返回一种 Object[]....但假设它是一个对象Custom的Arraylist，如何让toArray()返回Custom[]的类型而不是对象[]?

So, normally ArrayList.toArray() would return a type of Object[]....but supposed it's an Arraylist of object Custom, how do I make toArray() to return a type of Custom[] rather than Object[]?

推荐答案

像这样:

List<String> list = new ArrayList<String>();

String[] a = list.toArray(new String[0]);

在 Java6 之前，建议这样写:

Before Java6 it was recommended to write:

String[] a = list.toArray(new String[list.size()]);

因为内部实现无论如何都会重新分配一个大小合适的数组，所以你最好提前做.由于 Java6 首选空数组，请参阅 .toArray(new MyClass[0]) 或 .toArray(new MyClass[myList.size()])?

because the internal implementation would realloc a properly sized array anyway so you were better doing it upfront. Since Java6 the empty array is preferred, see .toArray(new MyClass[0]) or .toArray(new MyClass[myList.size()])?

如果您的列表类型不正确，您需要在调用 toArray 之前进行强制转换.像这样:

If your list is not properly typed you need to do a cast before calling toArray. Like this:

    List l = new ArrayList<String>();

    String[] a = ((List<String>)l).toArray(new String[l.size()]);

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