如何知道Stream.toArray(Book [] :: new);数组有多少个元素，"Book [] :: new"的实现在哪里 [英] How knows Stream.toArray(Book[]::new); how many elements the array has and where is the implementation of “Book[]::new”
问题描述
我试图理解方法引用，但是我不知道如何使用此"Book [] :: new"它可以创建一个 具有正确数量的元素的数组.
I'm triying to understand method references and I don't know how with this "Book[]::new" it can create an array with the right number of elements.
Book[] arrayBook = stBooks.toArray(Book[]::new);
为了在使用第二个和第三个选项时创建数组，我必须指定一个功能接口 会收到一个Int并返回一个新的数组.
In order to create the array when I use the second and third option I have to specify a Functional Interface that Receive an Int and return a new Array.
但是，在第一个选项中，我不知道实现在哪里以及您在哪里指定数字或 具有数组的元素.我认为它为每个Stream元素创建了一个新的array元素 但是如果我理解得很好，则必须提供实现和"Book [] :: new"没有它.
But, in the first option I don't know where is the implementation and where you specify the number or elements that is going to have the array. I figure that it create a new array element for each Stream element but if I understand well you have to provide the implementation and "Book[]::new" doesn't have it.
Book book1 = new Book("ESDLA");
Book book2 = new Book("Harry Potter");
Stream<Book> stBooks = Stream.of(book1, book2);
1. Method References
Book[] arrayBook = stBooks.toArray(Book[]::new);
2. With Lambda Implementation
Book[] arrayBook1 = stBooks.toArray( (numElements) -> new Book[numElements] );
3. With Implementation
Book[] arrayBook2 = stBooks.toArray( new IntFunction<Book[]>() {
@Override
public Book[] apply(int numElements) {
return new Book[numElements];
}
});
推荐答案
在
如果方法引用表达式的格式为 If the method reference expression has the form 还有，: 如果形式为 If the form is 因此，实现"是指您要查找的内容隐藏在Java编译器中的某处，因为它们都是编译器魔术". So the "implementation" that you want to find is hidden somewhere in the Java compiler, as it's all "compiler magic". 这篇关于如何知道Stream.toArray(Book [] :: new);数组有多少个元素，"Book [] :: new"的实现在哪里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！ArrayType::new，则将考虑单个概念方法.该方法具有单个int类型的参数，返回ArrayType，并且没有throws子句.如果n = 1，则这是唯一可能适用的方法；否则，没有可能适用的方法.
ArrayType::new, a single notional method is considered. The method has a single parameter of type int, returns the ArrayType, and has no throws clause. If n = 1, this is the only potentially applicable method; otherwise, there are no potentially applicable methods.
Type[]^k :: new(k≥1)，则调用方法的主体与形式为new Type [ size ] []^k-1的数组创建表达式具有相同的效果，其中size是调用方法的单个参数. (符号[]^k表示k个括号对的序列.)
Type[]^k :: new (k ≥ 1), then the body of the invocation method has the same effect as an array creation expression of the form new Type [ size ] []^k-1, where size is the invocation method's single parameter. (The notation []^k indicates a sequence of k bracket pairs.)
