为什么我可以在没有stream() - 方法的类的对象上调用stream()方法？

Question

我是大学新手Java程序员.我今天发现了一些关于Java语法如何工作的概念.

public class testClass {

ArrayList <String> persons = new ArrayList <String> ();

public void run(){
    Stream <String> personstream = persons.stream();
}}

stream()在ArrayList类中找不到该方法,但它可能看起来好像在那里.当我将鼠标移到stream()Eclipse中的-method上时,它表示它是Collections的一部分,但我stream()在其在线文档中找不到任何方法.

stream()如果它不是我从中调用它的类的一部分,为什么调用该方法呢？

Answer 1

你检查了正确的类和Java版本吗？Java 8 Collection(非Collections)有一个stream()默认方法,它由ArrayList以下方法继承:

/**
 * Returns a sequential {@code Stream} with this collection as its source.
 *
 * <p>This method should be overridden when the {@link #spliterator()}
 * method cannot return a spliterator that is {@code IMMUTABLE},
 * {@code CONCURRENT}, or <em>late-binding</em>. (See {@link #spliterator()}
 * for details.)
 *
 * @implSpec
 * The default implementation creates a sequential {@code Stream} from the
 * collection's {@code Spliterator}.
 *
 * @return a sequential {@code Stream} over the elements in this collection
 * @since 1.8
 */
default Stream<E> stream() {
    return StreamSupport.stream(spliterator(), false);
}